Hi all,

Following an earlier posting about my boiler, I'm sorry to report that
it wasn't working after all! Things were better, but after much more
experimentation, I've discovered that the fundemental problem is still
there. Old thread is here http://groups.google.com/group/uk.d-i-y/
browse_frm/thread/aff8767da598212

Anyway, I've got a Ravenheat RSF84ET combi boiler which is getting too
hot and so cutting out (after 20 seconds or so, it cools, so re-fires,
and the cycle starts again). This happens with the HW and CH.

The boiler uses a single heat exchanger for the CH and HW. In HW mode,
the diverter valve short-circuits the CH loop, so a small amount of
water is heated and pumped round and round the heat exchanger,
adjacent to the HW pipes. In CH mode, the CH loop operates through the
rads, as you would expect. The short CH loop (inside the boiler) has
a CH thermistor and overheat stat. If the loop gets above 85 degrees,
the CH thermistor tells the PCB to stop. If it goes closer to 100
degrees, the overheat stat just kills the 240V.

From my measurements with a spare thermistor, the CH loop gets above
85 degrees so it shuts off the flame. But I don't know why the loop
gets so hot! The manual points to the thermistors and potentiometers,
which have all been replaced.

Possible thoughts a

a) the pump is not working properly

b) the heat exchanger is scaled on the CH side (but I am in a nice
soft water area, and draining the system produced lovely clear water,
not black sludge!)

Both of these could theoretically stop the hot water getting away from
the boiler fast enough (although all 7 rads get nice and hot!).

How can I prove either of these thoughts? Any others?


Many thanks,
Richard.

In article .com,
Richard Walker writes

Possible thoughts a

a) the pump is not working properly

b) the heat exchanger is scaled on the CH side (but I am in a nice
soft water area, and draining the system produced lovely clear water,
not black sludge!)

Both of these could theoretically stop the hot water getting away from
the boiler fast enough (although all 7 rads get nice and hot!).

How can I prove either of these thoughts? Any others?

Did you work out whether it was modulating correctly?
--
fred
Plusnet - I hope you like vanilla

On Feb 7, 8:05 pm, fred wrote:

Did you work out whether it was modulating correctly?

I've just been re-running some tests, and can confirm that the gas
valve modulates correctly when I drive it with a variable power
supply. If I monitor the CH loop thermistor and adjust the modulation
voltage accordingly (anywhere between 0 and 15V, steadying around
12-13V), I can prevent the CH loop from reaching the magic 85 degrees
C and therefore it supplies nice hot water for ever!

I re-connected the control PCB to the gas valve modulator and measured
the voltage. Running the hot tap again showed the modulation voltage
start on a nice high 15V, but never shifting. I even turned down the
HW temperature potentiometer, and the modulation voltage didn't shift.

This kind of makes me think the PCB is refusing to modulate, so could
be broken. But why would only that aspect of the PCB be broken, when
everything else works fine?!

I did not try my (rather dodgy) manual modulation method with the CH
to see if I could get it to run without cutting out, but I assume I
could. In fact, I might give that a go now...


Many thanks,
Richard.

In article .com
, Richard Walker writes
On Feb 7, 8:05 pm, fred wrote:

Did you work out whether it was modulating correctly?

I've just been re-running some tests, and can confirm that the gas
valve modulates correctly when I drive it with a variable power
supply. If I monitor the CH loop thermistor and adjust the modulation
voltage accordingly (anywhere between 0 and 15V, steadying around
12-13V), I can prevent the CH loop from reaching the magic 85 degrees
C and therefore it supplies nice hot water for ever!

I re-connected the control PCB to the gas valve modulator and measured
the voltage. Running the hot tap again showed the modulation voltage
start on a nice high 15V, but never shifting. I even turned down the
HW temperature potentiometer, and the modulation voltage didn't shift.

This kind of makes me think the PCB is refusing to modulate, so could
be broken. But why would only that aspect of the PCB be broken, when
everything else works fine?!

I did not try my (rather dodgy) manual modulation method with the CH
to see if I could get it to run without cutting out, but I assume I
could. In fact, I might give that a go now...

That's a major step forward I think, you now know that the gas valve and
the modulator are working fine. It certainly now points to the pcb or the
sensors feeding it. How about now replacing any temp sensing thermistors
with variable resisitors to see if you can manually control and modulate the
boiler with them. If you can then it points to faulty sensors, if you can't
then it's moving back to the pcb. As to one part of the pcb working while
another doesn't, that doesn't surprise me at all, different functions in
different sections of the pcb mean one function can work while another
doesn't. I haven't re-read all of the old thread so don't know if you've already
tried changing the pcb.
--
fred
Plusnet - I hope you like vanilla

In message .com,
Richard Walker writes
On Feb 7, 8:05 pm, fred wrote:

Did you work out whether it was modulating correctly?

I've just been re-running some tests, and can confirm that the gas
valve modulates correctly when I drive it with a variable power
supply. If I monitor the CH loop thermistor and adjust the modulation
voltage accordingly (anywhere between 0 and 15V, steadying around
12-13V), I can prevent the CH loop from reaching the magic 85 degrees
C and therefore it supplies nice hot water for ever!

I re-connected the control PCB to the gas valve modulator and measured
the voltage. Running the hot tap again showed the modulation voltage
start on a nice high 15V, but never shifting. I even turned down the
HW temperature potentiometer, and the modulation voltage didn't shift.

This kind of makes me think the PCB is refusing to modulate, so could
be broken. But why would only that aspect of the PCB be broken, when
everything else works fine?!

Why not ?

it's a control loop driving a LV power transistor I presume

if anything in that loop has gone (the driver transistor for example),
it won't necessarily work properly, but that's no reason for the rest of
the pcb not to work
--
geoff

On Feb 7, 9:48 pm, fred wrote:
In article .com

, Richard Walker writes
On Feb 7, 8:05 pm, fred wrote:

Did you work out whether it was modulating correctly?

I've just been re-running some tests, and can confirm that the gas
valve modulates correctly when I drive it with a variable power
supply. If I monitor the CH loop thermistor and adjust the modulation
voltage accordingly (anywhere between 0 and 15V, steadying around
12-13V), I can prevent the CH loop from reaching the magic 85 degrees
C and therefore it supplies nice hot water for ever!

I re-connected the control PCB to the gas valve modulator and measured
the voltage. Running the hot tap again showed the modulation voltage
start on a nice high 15V, but never shifting. I even turned down the
HW temperature potentiometer, and the modulation voltage didn't shift.

This kind of makes me think the PCB is refusing to modulate, so could
be broken. But why would only that aspect of the PCB be broken, when
everything else works fine?!

I did not try my (rather dodgy) manual modulation method with the CH
to see if I could get it to run without cutting out, but I assume I
could. In fact, I might give that a go now...

That's a major step forward I think, you now know that the gas valve and
the modulator are working fine. It certainly now points to the pcb or the
sensors feeding it. How about now replacing any temp sensing thermistors
with variable resisitors to see if you can manually control and modulate the
boiler with them. If you can then it points to faulty sensors, if you can't
then it's moving back to the pcb.

I have tried using spare thermistors just dangling in the air, so they
don't realise things are getting hot. Unfortunately, the CH loop gets
hotter and hotter, rather close to 95 degrees C (at which point, the
overheat stat kicks in!).

I tested the PCB modulation with the CH, and found that the PCB does
actually vary the voltage. It starts at 10V, and modulates down to
almost nothing in the space of 10 minutes (once the rads are all
hot). Unfortunately, even at minimum flame, the CH loop still gets
too hot and the thermistor intervenes and cuts the flame.

I've also tried the manual modulation method with the CH, and it
doesn't work! The CH loop gets too hot, even with the modulation set
to 0V (minimum). So, my manual method is exactly the same as the PCB
for CH (although for HW, the PCB always uses 15V).

As to one part of the pcb working while
another doesn't, that doesn't surprise me at all, different functions in
different sections of the pcb mean one function can work while another
doesn't. I haven't re-read all of the old thread so don't know if you've already
tried changing the pcb.

No, I have not tried changing the PCB. I was kind of assuming they
were an all-or-nothing affair. The CH modulation seems to work, so I
find it rather hard to believe that only the DHW modulation function
is broken!

I suppose that if the PCB is OK, then it does rather suggest that the
CH loop is not able to circulate properly. Duff pump, or partial
blockage, maybe?!

Many thanks for your comments.


Cheers,
Richard.

In article . com,
Richard Walker writes
On Feb 7, 9:48 pm, fred wrote:
In article .com

, Richard Walker writes
On Feb 7, 8:05 pm, fred wrote:

Did you work out whether it was modulating correctly?

I've just been re-running some tests, and can confirm that the gas
valve modulates correctly when I drive it with a variable power
supply. If I monitor the CH loop thermistor and adjust the modulation
voltage accordingly (anywhere between 0 and 15V, steadying around
12-13V), I can prevent the CH loop from reaching the magic 85 degrees
C and therefore it supplies nice hot water for ever!

I re-connected the control PCB to the gas valve modulator and measured
the voltage. Running the hot tap again showed the modulation voltage
start on a nice high 15V, but never shifting. I even turned down the
HW temperature potentiometer, and the modulation voltage didn't shift.

This kind of makes me think the PCB is refusing to modulate, so could
be broken. But why would only that aspect of the PCB be broken, when
everything else works fine?!

I did not try my (rather dodgy) manual modulation method with the CH
to see if I could get it to run without cutting out, but I assume I
could. In fact, I might give that a go now...

That's a major step forward I think, you now know that the gas valve and
the modulator are working fine. It certainly now points to the pcb or the
sensors feeding it. How about now replacing any temp sensing thermistors
with variable resisitors to see if you can manually control and modulate the
boiler with them. If you can then it points to faulty sensors, if you can't
then it's moving back to the pcb.

I have tried using spare thermistors just dangling in the air, so they
don't realise things are getting hot. Unfortunately, the CH loop gets
hotter and hotter, rather close to 95 degrees C (at which point, the
overheat stat kicks in!).

I tested the PCB modulation with the CH, and found that the PCB does
actually vary the voltage. It starts at 10V, and modulates down to
almost nothing in the space of 10 minutes (once the rads are all
hot). Unfortunately, even at minimum flame, the CH loop still gets
too hot and the thermistor intervenes and cuts the flame.

I've also tried the manual modulation method with the CH, and it
doesn't work! The CH loop gets too hot, even with the modulation set
to 0V (minimum). So, my manual method is exactly the same as the PCB
for CH (although for HW, the PCB always uses 15V).

As to one part of the pcb working while
another doesn't, that doesn't surprise me at all, different functions in
different sections of the pcb mean one function can work while another
doesn't. I haven't re-read all of the old thread so don't know if you've already
tried changing the pcb.

No, I have not tried changing the PCB. I was kind of assuming they
were an all-or-nothing affair. The CH modulation seems to work, so I
find it rather hard to believe that only the DHW modulation function
is broken!

I suppose that if the PCB is OK, then it does rather suggest that the
CH loop is not able to circulate properly. Duff pump, or partial
blockage, maybe?!

Sorry matey, thought it was your DHW side that was screwed up, not your
CH. The fact that the boiler is cycling so quickly suggests to me (as a
non-expert) some flow issue. Is it possible the diverter is stuck on a little
(or leaking) and the CH loop is being short circuited (even partially), that
would result in no (or reduced) CH flow, no DHW demand so nowhere for
the heat to go, hence the fast cycling. Don't know if your diverter has a
diaphragm but it's a bit of a classic for splits & leaks, also a sticking
diverter.
--
fred
Plusnet - I hope you like vanilla

On Feb 7, 11:35 pm, fred wrote:
In article . com,
Richard Walker writes

I suppose that if the PCB is OK, then it does rather suggest that the
CH loop is not able to circulate properly. Duff pump, or partial
blockage, maybe?!

Sorry matey, thought it was your DHW side that was screwed up, not your
CH.

Sorry, I probably didn't explain it too well!

The fact that the boiler is cycling so quickly suggests to me (as a
non-expert) some flow issue.

Tallies with my current thinking (pump or heat exchanger).

Is it possible the diverter is stuck on a little
(or leaking) and the CH loop is being short circuited (even partially),

The diverter seems to be working OK - it doesn't pass to the full CH
circuit when it is asked to link in the HW. I'll see if I can check
it in CH mode, though.

I guess it could be rather sludged up which would screw up the flow?

that
would result in no (or reduced) CH flow, no DHW demand so nowhere for
the heat to go, hence the fast cycling. Don't know if your diverter has a
diaphragm but it's a bit of a classic for splits & leaks, also a sticking
diverter.

Yes, in fact, I think I've got a diaphragm repair kit somewhere...

It looks like I need to remove all these bits and have a good look at
them.


Cheers,
Richard,

On 7 Feb, 22:09, raden wrote:
In message .com,RichardWalker writes

This kind of makes me think the PCB is refusing to modulate, so could
be broken. But why would only that aspect of the PCB be broken, when
everything else works fine?!

Why not ?

it's a control loop driving a LV power transistor I presume

if anything in that loop has gone (the driver transistor for example),
it won't necessarily work properly, but that's no reason for the rest of
the pcb not to work

(It seems that my first reply vanished!)

I suppose so. I was just thinking that if the PCB works in all other
aspects, including CH modulation, it's strange that the HW modulation
fails! Perhaps I have the logic wrong in my head, and something else
is supposed to happen before the PCB modulated the HW?

In CH mode, the boiler still overheats when it's modulating on minimum
(either via the PCB or manually), which I suppose shouldn't happen.

I'm starting to think that there is a 'wet' problem with circulation
in the CH loop, and possibly also a PCB problem (which may be why it
doesn't modulate on the HW).


Cheers,
Richard.

On Thu, 08 Feb 2007 02:31:23 -0800, Richard Walker wrote:

On 7 Feb, 22:09, raden wrote:
In message .com,RichardWalker writes

This kind of makes me think the PCB is refusing to modulate, so could
be broken. But why would only that aspect of the PCB be broken, when
everything else works fine?!

Why not ?

it's a control loop driving a LV power transistor I presume

if anything in that loop has gone (the driver transistor for example),
it won't necessarily work properly, but that's no reason for the rest of
the pcb not to work

(It seems that my first reply vanished!)

I suppose so. I was just thinking that if the PCB works in all other
aspects, including CH modulation, it's strange that the HW modulation
fails! Perhaps I have the logic wrong in my head, and something else
is supposed to happen before the PCB modulated the HW?

In CH mode, the boiler still overheats when it's modulating on minimum
(either via the PCB or manually), which I suppose shouldn't happen.

I'm starting to think that there is a 'wet' problem with circulation
in the CH loop, and possibly also a PCB problem (which may be why it
doesn't modulate on the HW).


You've done all the easy stuff. The modulation on the DHW side of things
is a critical function.

I think it's time that you bit the bullet and tried a new PCB. If you're
lucky cetltd do one. If not is HRPC or keeptheheaton or that ilk.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Wed, 07 Feb 2007 14:11:59 -0800, Richard Walker wrote:

On Feb 7, 9:48 pm, fred wrote:
In article .com

, Richard Walker writes
On Feb 7, 8:05 pm, fred wrote:

Did you work out whether it was modulating correctly?

I've just been re-running some tests, and can confirm that the gas
valve modulates correctly when I drive it with a variable power
supply. If I monitor the CH loop thermistor and adjust the modulation
voltage accordingly (anywhere between 0 and 15V, steadying around
12-13V), I can prevent the CH loop from reaching the magic 85 degrees
C and therefore it supplies nice hot water for ever!

I re-connected the control PCB to the gas valve modulator and measured
the voltage. Running the hot tap again showed the modulation voltage
start on a nice high 15V, but never shifting. I even turned down the
HW temperature potentiometer, and the modulation voltage didn't shift.

This kind of makes me think the PCB is refusing to modulate, so could
be broken. But why would only that aspect of the PCB be broken, when
everything else works fine?!

I did not try my (rather dodgy) manual modulation method with the CH
to see if I could get it to run without cutting out, but I assume I
could. In fact, I might give that a go now...

That's a major step forward I think, you now know that the gas valve and
the modulator are working fine. It certainly now points to the pcb or the
sensors feeding it. How about now replacing any temp sensing thermistors
with variable resisitors to see if you can manually control and modulate the
boiler with them. If you can then it points to faulty sensors, if you can't
then it's moving back to the pcb.

I have tried using spare thermistors just dangling in the air, so they
don't realise things are getting hot. Unfortunately, the CH loop gets
hotter and hotter, rather close to 95 degrees C (at which point, the
overheat stat kicks in!).

I tested the PCB modulation with the CH, and found that the PCB does
actually vary the voltage. It starts at 10V, and modulates down to
almost nothing in the space of 10 minutes (once the rads are all
hot). Unfortunately, even at minimum flame, the CH loop still gets
too hot and the thermistor intervenes and cuts the flame.

I've also tried the manual modulation method with the CH, and it
doesn't work! The CH loop gets too hot, even with the modulation set
to 0V (minimum). So, my manual method is exactly the same as the PCB
for CH (although for HW, the PCB always uses 15V).

As to one part of the pcb working while
another doesn't, that doesn't surprise me at all, different functions in
different sections of the pcb mean one function can work while another
doesn't. I haven't re-read all of the old thread so don't know if you've already
tried changing the pcb.

No, I have not tried changing the PCB. I was kind of assuming they
were an all-or-nothing affair. The CH modulation seems to work, so I
find it rather hard to believe that only the DHW modulation function
is broken!

I suppose that if the PCB is OK, then it does rather suggest that the
CH loop is not able to circulate properly. Duff pump, or partial
blockage, maybe?!


The boiler heats all the radiators in 10 minutes, so you say. It is most
unlikely that there is a duff pump or partial blockage in the primary.

Is there a separate sensor for the DHW? If so and the sensor has been
verified then it's likely the PCB. The modulator driving circuits are OK
but perhaps the DHW sensing circuits are duff?

The only blockage there could be is in the secondary heat exchanger (but
ISTR vaguely that you check that out). Even so I would expect the boiler
to modulate rapidly from max to min before cutting out on DHW.

HTH

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Feb 9, 7:28 pm, Ed Sirett wrote:
On Wed, 07 Feb 2007 14:11:59 -0800, Richard Walker wrote:

I suppose that if the PCB is OK, then it does rather suggest that the
CH loop is not able to circulate properly. Duff pump, or partial
blockage, maybe?!

The boiler heats all the radiators in 10 minutes, so you say.

Yes. And on CH-only, the boiler keeps re-firing then dying for short
periods (sometimes it will fire for as little as 10 seconds before
deciding it's too hot, then wait for 30 seconds, then start again).

It is most
unlikely that there is a duff pump or partial blockage in the primary.

Hmm.

Is there a separate sensor for the DHW? If so and the sensor has been
verified

Yes, there is a wet thermistor on the DHW output pipe from the heat
exchanger (boiler has a single-piece heat exchanger for DHW and CH).

I believe that the value from this sensor should determine the
modulation level, but although the sensor is definately OK (was
replaced as a precaution) the PCB doesn't bother to modulate down the
gas.

then it's likely the PCB. The modulator driving circuits are OK
but perhaps the DHW sensing circuits are duff?

Yeah, that makes sense for DHW.

However, when in CH mode, the boiler cycles (as I say above), even
though there is an anti-cycle device which should prevent this for at
least 2.5 minutes.

The only blockage there could be is in the secondary heat exchanger (but
ISTR vaguely that you check that out).

I see. So the CH side of the exchanger could be blocked?

Even so I would expect the boiler
to modulate rapidly from max to min before cutting out on DHW.

That is exactly what happens on the CH side - it starts off with a
high-ish flame, then as the CH loop warms up, it reduces down.
Eventually, it gets to minimum modulation, yet the CH loop is still
too hot (so the flame dies).

Perhaps I've got two problems he

a) iffy PCB in DHW mode, possibly re. the DHW temperature sensing, as
you say

b) poor flow on the CH loop (heat exchanger, pump or diverter?)

???

I think I can get hold of a new pump and diverter, so might try taking
them out and checking for blockages. Depending on my findings, I
could then be on the hunt for a PCB...

Anyone tried this sort of thing before? Any tips on removing these
wet parts and flushing?


Cheers,
Richard.

On Sat, 10 Feb 2007 03:01:18 -0800, Richard Walker wrote:

On Feb 9, 7:28 pm, Ed Sirett wrote:
On Wed, 07 Feb 2007 14:11:59 -0800, Richard Walker wrote:

I suppose that if the PCB is OK, then it does rather suggest that the
CH loop is not able to circulate properly. Duff pump, or partial
blockage, maybe?!

The boiler heats all the radiators in 10 minutes, so you say.

Yes. And on CH-only, the boiler keeps re-firing then dying for short
periods (sometimes it will fire for as little as 10 seconds before
deciding it's too hot, then wait for 30 seconds, then start again).


If there are TRVs and they have mostly closed then you could get that
behaviour.
I'm not familiar with this model there may be a bypass circuit.
Or more simply the required heating load is 1/4 of the minimum power
(typically 10kW) so 2.5kW to keep things warm.



It is most
unlikely that there is a duff pump or partial blockage in the primary.

Hmm.
I'm sticking by that. If the boiler heats the rads in 10 minutes a
significant heat transfer has taken place.



Is there a separate sensor for the DHW? If so and the sensor has been
verified

Yes, there is a wet thermistor on the DHW output pipe from the heat
exchanger (boiler has a single-piece heat exchanger for DHW and CH).

Is is a tube-in-tube type that has to keep the primary circulator going in
DHW mode; the heat transfer is then gas-metal-primary water-metal-DHW.
Or is it more like a Ferroli with two direct exchangers in one unit?


I believe that the value from this sensor should determine the
modulation level, but although the sensor is definately OK (was
replaced as a precaution) the PCB doesn't bother to modulate down the
gas.

then it's likely the PCB. The modulator driving circuits are OK
but perhaps the DHW sensing circuits are duff?

Yeah, that makes sense for DHW.

However, when in CH mode, the boiler cycles (as I say above), even
though there is an anti-cycle device which should prevent this for at
least 2.5 minutes.

The anti cycle device might only operate on the external control i.e. if
the thermostat goes off and then on the boiler will impose a minimum 2.5
mins, but not on the internal stat?


The only blockage there could be is in the secondary heat exchanger (but
ISTR vaguely that you check that out).

I see. So the CH side of the exchanger could be blocked?

Even so I would expect the boiler
to modulate rapidly from max to min before cutting out on DHW.

That is exactly what happens on the CH side - it starts off with a
high-ish flame, then as the CH loop warms up, it reduces down.
Eventually, it gets to minimum modulation, yet the CH loop is still
too hot (so the flame dies).

That's exactly what it should do. After that it short cycles on the sensor
between off and min. Remind me how few rads you have?


Perhaps I've got two problems he

a) iffy PCB in DHW mode, possibly re. the DHW temperature sensing, as
you say


b) poor flow on the CH loop (heat exchanger, pump or diverter?)
I doubt it.
A) The rads get hot in 10 mins.
The diverter valve simply short circuits the primary - in which case you
almost certainly have a tube-in-tube type heat exchanger, which means the
circulator must run in DHW mode.

What might be happening is that there is a problem getting the heat into
the DHW. The primary is getting too hot so the gas has to be cut. This is
being picked up by the CH sensor not the DHW sensor.

If you are in a hard water area I'd say that the DHW side of the exchanger
is full of chalk.

I've lost track of the original symptoms IIRC they we

CH OK.
DHW cycles between warm and off.
Boiler is cycling between min modulation and off in DHW.
DHW unusable because of the fluctuations.

The boiler has a tube-in-tube one piece heat exchanger (I guess)
The diverter valve simply short circuits the rads in DHW mode (I guess).
The pump is OK (cause the CH works OK).
The burner is OK
The sensors are OK, both of them.
The PCB is only a bit broken if at all.

I'd say if I cam across this and it was a hard water area that we are
looking at chalk in the DHW exchanger. Just possibly crud on inside the
primary heat exchanger - but the CH works well so can't be too much wrong.

In a sof****er area you'd have to go for the PCB somewhat in hope over
desparation.

If you are in a hard water area and don't have a descaling pump then you
will have to find a
a) bucket/bowl capable of immersing the entire heat exchanger in.
b) remove the heat Xer
c) obtain 5litre of screwfix patio cleaner say adding water to cover.
d) put unit in bowl add acid leave for several hours turning occasionally
to get new acid into the tubes.

You could also spend a couple of hundred on a new unit and refurb the old
one in readiness for the second run of this problem in a year or two.




???

I think I can get hold of a new pump and diverter, so might try taking
them out and checking for blockages. Depending on my findings, I
could then be on the hunt for a PCB...

Anyone tried this sort of thing before? Any tips on removing these
wet parts and flushing?


Cheers,
Richard.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

Hi Ed,

Thank you very much for your detailed reply.


On Feb 10, 11:50 am, Ed Sirett wrote:
On Sat, 10 Feb 2007 03:01:18 -0800, Richard Walker wrote:

And on CH-only, the boiler keeps re-firing then dying for short
periods (sometimes it will fire for as little as 10 seconds before
deciding it's too hot, then wait for 30 seconds, then start again).

If there are TRVs and they have mostly closed then you could get that
behaviour.

I should have said: I don't have any TRVs, although all but one rad
has the return valve open only one turn (just to balance the system -
otherwise, one of the rads does not heat at all!). For what it's
worth, there is a room stat, and I could always short this out to
eliminate it.

I'm not familiar with this model there may be a bypass circuit.

An external bypass should be fitted according to the book. In the
pipework just below and boiler, the CH flow and return are linked with
a gate valve which is open two turns. If I close this completely, the
pump makes a dreadful racket when the CH is on!

It is most unlikely that there is a duff pump or partial blockage in the primary.

I'm sticking by that. If the boiler heats the rads in 10 minutes a
significant heat transfer has taken place.

Makes sense. Also, when I run the DHW, before the boiler cuts out,
the water does get VERY hot and it comes out very fast!

There is a wet thermistor on the DHW output pipe from the heat
exchanger (boiler has a single-piece heat exchanger for DHW and CH).

Is is a tube-in-tube type that has to keep the primary circulator going in
DHW mode; the heat transfer is then gas-metal-primary water-metal-DHW.
Or is it more like a Ferroli with two direct exchangers in one unit?

The manual describes the exchanger as a 'double parallel' type which
uses the 'countercurrent system' for DHW. From the picture in the
manual, it looks like a tube-in-tube. And yes, the pump runs in DHW
mode.

However, when in CH mode, the boiler cycles (as I say above), even
though there is an anti-cycle device which should prevent this for at
least 2.5 minutes.

The anti cycle device might only operate on the external control i.e. if
the thermostat goes off and then on the boiler will impose a minimum 2.5
mins, but not on the internal stat?

Maybe. The manual doesn't say much: only that the anti-cycle stops
the CH re-firing for 2.5 minutes, and that the DHW operation is not
affected.

That is exactly what happens on the CH side - it starts off with a
high-ish flame, then as the CH loop warms up, it reduces down.
Eventually, it gets to minimum modulation, yet the CH loop is still
too hot (so the flame dies).

That's exactly what it should do. After that it short cycles on the sensor
between off and min. Remind me how few rads you have?

I've got 7 in the house (small three-bed semi).

The cycles are VERY short, however. The flame stops, then within
about 30 seconds, the boiler starts up and fires for maybe only 10
seconds. This is why I wonder if the CH loop is getting too hot.

b) poor flow on the CH loop (heat exchanger, pump or diverter?)

I doubt it.
A) The rads get hot in 10 mins.

True.

The diverter valve simply short circuits the primary - in which case you
almost certainly have a tube-in-tube type heat exchanger, which means the
circulator must run in DHW mode.

Yes, that's correct. I was also wondering if the diverter could be
blocked.

What might be happening is that there is a problem getting the heat into
the DHW. The primary is getting too hot so the gas has to be cut. This is
being picked up by the CH sensor not the DHW sensor.

Yes. I've just made another discovery: the DHW sensor doesn't appear
to be powered-up by the control PCB! No wonder the boiler doesn't
realise the water is getting hot and that it should modulate down!

The sensor does work (the resistances are good) but when the PCB is
connected, it always shows 0V, whereas the CH sensor will be at approx
3V when the loop is warm. i have also checked the wiring loom between
the PCB and the sensor, and this checks out OK.

I suppose this explains why the CH does modulate and the DHW does not.

If you are in a hard water area I'd say that the DHW side of the exchanger
is full of chalk.

Thing is, the water is nice and soft here. :-/

I've lost track of the original symptoms IIRC they we

CH OK.

Yes, apart from the excessive cycling when the CH has got warm (after
being on for 10 minutes).

DHW cycles between warm and off.
Boiler is cycling between min modulation and off in DHW.
DHW unusable because of the fluctuations.

Yes. Although I may have just discovered why (DHW sensor not live).

The boiler has a tube-in-tube one piece heat exchanger (I guess)
The diverter valve simply short circuits the rads in DHW mode (I guess).

Yes.

The pump is OK (cause the CH works OK).

If I can assume it's OK because all 7 rads warm up nicely in 10
minutes, then yes, it must be OK.

The burner is OK
The sensors are OK, both of them.

Yes.

The PCB is only a bit broken if at all.

Possibly. It is not powering (so therefore not able to read) the DHW
sensor so cannot modulate on DHW. And the anti-cycle doesn't seem to
work on CH mode.

I'd say if I cam across this and it was a hard water area that we are
looking at chalk in the DHW exchanger. Just possibly crud on inside the
primary heat exchanger - but the CH works well so can't be too much wrong.

OK.

In a sof****er area you'd have to go for the PCB somewhat in hope over
desparation.

Then perhaps this is where I am.

If you are in a hard water area and don't have a descaling pump then you
will have to find a
a) bucket/bowl capable of immersing the entire heat exchanger in.
b) remove the heat Xer
c) obtain 5litre of screwfix patio cleaner say adding water to cover.
d) put unit in bowl add acid leave for several hours turning occasionally
to get new acid into the tubes.

You could also spend a couple of hundred on a new unit and refurb the old
one in readiness for the second run of this problem in a year or two.

Yes, I can see me having to do that if I do end up cleaning the
exchanger, and manage to break it!


Cheers,
Richard.

On Sat, 10 Feb 2007 10:31:28 -0800, Richard Walker wrote:

Hi Ed,

Thank you very much for your detailed reply.


snip

I'd say if I cam across this and it was a hard water area that we are
looking at chalk in the DHW exchanger. Just possibly crud on inside the
primary heat exchanger - but the CH works well so can't be too much wrong.

OK.

In a sof****er area you'd have to go for the PCB somewhat in hope over
desparation.

Then perhaps this is where I am.


I think you have found the smoking gun with there being no volts on the
DHW sensor. Could it be a simple bad connection?

Otherwise the PCB really is the trouble.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Feb 10, 10:06 pm, Ed Sirett wrote:
On Sat, 10 Feb 2007 10:31:28 -0800, Richard Walker wrote:

In a sof****er area you'd have to go for the PCB somewhat
in hope over desparation.

Then perhaps this is where I am.

I think you have found the smoking gun with there being no volts on the
DHW sensor.

Yes, this makes sense. And I'm also wondering if the CH anti-cycle
function is broken.

Could it be a simple bad connection?

I wondered this when I discovered the zero volts, so I bypassed the
wiring loom and measured directly from the PCB - still zero volts.
OK, so maybe there is a tiny dry joint, crack, single component
failure somewhere on the PCB, but I'll never find it in a million
years!

Otherwise the PCB really is the trouble.

Sounds like it, doesn't it? I'll see what I can get hold of, and I'll
post pack with my results. Fingers crossed!


Cheers,
Richard.

On Feb 11, 11:39 am, "Richard Walker"
wrote:
On Feb 10, 10:06 pm, Ed Sirett wrote:

Otherwise the PCB really is the trouble.

Sounds like it, doesn't it? I'll see what I can get hold of, and I'll
post pack with my results. Fingers crossed!

I found a local engineer who carries plenty of Ravenheat spares (and
will actually work on them, rather than complain about DIYers!). We
tried fitting a new PCB. Result: exactly the same. I couldn't
believe it!

Almost by fluke, he decided to change the wiring loom which runs from
the PCB to the DHW potentiometer and DHW thermistor, as he had a spare
one. Result: voltage present on DHW thermistor! Then we put my PCB
back in. Result: the same, voltage still present on DHW thermistor!
Hurrah!

The reason I didn't spot the problem in the wire is because I tested
the loom from the sensor ends to the 'top' of the PCB plug. If I'd
tested to the bottom of the PCB plug (or direct from the PCB) I would
have seen that the PCB was fine, and the plug was shafted. D'oh!

Anyway, the boiler now seems to measure the DHW temperature and
modulate the gas valve accordingly (I can hear the valve clicking
slightly as it does this). The DHW is a lot more reliable.

However... it will still sometimes cut-out, wait 5-10 seconds, then re-
fire when running the DHW. The CH does something similar once the
rads are all up to temperature (I think the anti-cycle is too basic to
counter this).

So... We're thinking that the CH loop is not flowing adequately (so
the CH thermistor gets too hot). Blocked pump, diverter and/or heat
exchanger? Anyone know of anything I can try before I strip these
parts down (looks quite difficult, and a job for child-like hands!).


Cheers,
Richard.

On Wed, 14 Feb 2007 11:58:40 -0800, Richard Walker wrote:

On Feb 11, 11:39 am, "Richard Walker"
wrote:
On Feb 10, 10:06 pm, Ed Sirett wrote:

Otherwise the PCB really is the trouble.

Sounds like it, doesn't it? I'll see what I can get hold of, and I'll
post pack with my results. Fingers crossed!

I found a local engineer who carries plenty of Ravenheat spares (and
will actually work on them, rather than complain about DIYers!). We
tried fitting a new PCB. Result: exactly the same. I couldn't
believe it!

Almost by fluke, he decided to change the wiring loom which runs from
the PCB to the DHW potentiometer and DHW thermistor, as he had a spare
one. Result: voltage present on DHW thermistor! Then we put my PCB
back in. Result: the same, voltage still present on DHW thermistor!
Hurrah!

The reason I didn't spot the problem in the wire is because I tested
the loom from the sensor ends to the 'top' of the PCB plug. If I'd
tested to the bottom of the PCB plug (or direct from the PCB) I would
have seen that the PCB was fine, and the plug was shafted. D'oh!

Anyway, the boiler now seems to measure the DHW temperature and
modulate the gas valve accordingly (I can hear the valve clicking
slightly as it does this). The DHW is a lot more reliable.

However... it will still sometimes cut-out, wait 5-10 seconds, then re-
fire when running the DHW. The CH does something similar once the
rads are all up to temperature (I think the anti-cycle is too basic to
counter this).

So... We're thinking that the CH loop is not flowing adequately (so
the CH thermistor gets too hot). Blocked pump, diverter and/or heat
exchanger? Anyone know of anything I can try before I strip these
parts down (looks quite difficult, and a job for child-like hands!).



You now have a working boiler - the short cylcing on the CH is probably
the way it's made.

To stop the cycling in DHW mode you either need to improved the flow rate
on the DHW and/or increase the maximum DHW temp.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Feb 14, 9:45 pm, Ed Sirett wrote:
On Wed, 14 Feb 2007 11:58:40 -0800, Richard Walker wrote:

So... We're thinking that the CH loop is not flowing adequately (so
the CH thermistor gets too hot). Blocked pump, diverter and/or heat
exchanger? Anyone know of anything I can try before I strip these
parts down (looks quite difficult, and a job for child-like hands!).

You now have a working boiler - the short cylcing on the CH is probably
the way it's made.

Perhaps, but the handbook says there is an anti-cycle function which
should stop re-firing for 2.5 minutes. It re-fires well within that
time. Mind you, perhaps it's just not very good!

To stop the cycling in DHW mode you either need to improved the flow rate
on the DHW and/or increase the maximum DHW temp.

I've been monitoring the temperature of the short CH loop (when in DHW
mode). It always cuts when the CH thermistor resistance falls to
1.2k, which is approximately 85 degrees C.

I have backed the DHW temperature potentiometer off to about half-way,
and the DHW still comes out pretty hot. The modulation kicks-in
sooner, and the CH loop doesn't get to 1.2k, so it doesn't cut out. I
can run the hot tap for ages and ages. This is excellent!

I also noticed that the CH loop will overheat much sooner if I turn
the pump speed down (it was on max).

In CH mode, the boiler dies when the CH loop reaches 1.2k (just like
DHW mode) and it will re-fire at 2.3k. It only takes about 25 seconds
for the loop to reach 1.2k again, and shut off!

My question, perhaps to all combi boiler owners: is this normal?
Should the CH loop get too hot when it's running on max DHW
temperature? And is cycling inevitable once the rads are hot?


Cheers,
Richard.

On Thu, 15 Feb 2007 11:36:09 -0800, Richard Walker wrote:

On Feb 14, 9:45 pm, Ed Sirett wrote:
On Wed, 14 Feb 2007 11:58:40 -0800, Richard Walker wrote:

So... We're thinking that the CH loop is not flowing adequately (so
the CH thermistor gets too hot). Blocked pump, diverter and/or heat
exchanger? Anyone know of anything I can try before I strip these
parts down (looks quite difficult, and a job for child-like hands!).

You now have a working boiler - the short cylcing on the CH is probably
the way it's made.

Perhaps, but the handbook says there is an anti-cycle function which
should stop re-firing for 2.5 minutes. It re-fires well within that
time. Mind you, perhaps it's just not very good!

Have you check whether the feature applies to the external control rather
than the internal themrostat? Simple turn the WALL thermostat down for a
few seconds and back up again and see how the system reacts.



To stop the cycling in DHW mode you either need to improved the flow rate
on the DHW and/or increase the maximum DHW temp.

I've been monitoring the temperature of the short CH loop (when in DHW
mode). It always cuts when the CH thermistor resistance falls to
1.2k, which is approximately 85 degrees C.

I have backed the DHW temperature potentiometer off to about half-way,
and the DHW still comes out pretty hot.

Yes turn it lower if you provided that does not cause the burner to cycle.

The modulation kicks-in
sooner, and the CH loop doesn't get to 1.2k, so it doesn't cut out. I
can run the hot tap for ages and ages. This is excellent!

I also noticed that the CH loop will overheat much sooner if I turn
the pump speed down (it was on max).

And should be left there, otherwise you won't get the full DHW performance.


In CH mode, the boiler dies when the CH loop reaches 1.2k (just like
DHW mode) and it will re-fire at 2.3k. It only takes about 25 seconds
for the loop to reach 1.2k again, and shut off!

Better boilers can be instructed to not do full power for CH, they
also have anti-cycle delays that work.



My question, perhaps to all combi boiler owners: is this normal?
More or less for lower end kit.

Should the CH loop get too hot when it's running on max DHW
temperature?
Yes if there is scaling and/or poor DHW flow.

And is cycling inevitable once the rads are hot?
Maybe for this model.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Thu, 15 Feb 2007 20:47:56 +0000, Ed Sirett wrote:

And is cycling inevitable once the rads are hot?
Maybe for this model.

This may be a stock fault (or feature?) for this model. I know of one
that does almost exactly what the OP is describing (for CH at least -
seems to be OK on DHW).

On Feb 15, 8:47 pm, Ed Sirett wrote:
On Thu, 15 Feb 2007 11:36:09 -0800, Richard Walker wrote:
Ed Wrote:
You now have a working boiler - the short cylcing on the CH is probably
the way it's made.

Perhaps, but the handbook says there is an anti-cycle function which
should stop re-firing for 2.5 minutes. It re-fires well within that
time. Mind you, perhaps it's just not very good!

Have you check whether the feature applies to the external control rather
than the internal themrostat? Simple turn the WALL thermostat down for a
few seconds and back up again and see how the system reacts.

I've just tried this, and the boiler does as soon as you reduce the
stat, then re-fires as soon as I turn it up! If I reduce the CH
potentiometer, the boiler simply cuts out sooner (at, say, 1.3k
instead of 1.2k resistance on the CH thermistor). Not much of an anti-
cycle, really!

The user manual claims that when the boiler reaches its set maximum
temperature (whatever that is!), it will not operate on heating for 3
minutes. The installer guide says 2.5 minutes!

I have backed the DHW temperature potentiometer off to about half-way,
and the DHW still comes out pretty hot.

Yes turn it lower if you provided that does not cause the burner to cycle.

OK. I've had it at just over half-way and ran gallons of hot water,
varying the flow every not and again. Not a single cut-out. If I put
the tap onto full flow, the water doesn't get quite so hot, but I
suppose that's because it's only a 24 kW combi.

Thing is, though... the user instructions say that the DHW
potentiometer should vary the water temp between 35 and 65 degrees C,
and that operating it on max is OK (the CH potentiometer should select
between 40 and 85 degrees C).

And should be left there, otherwise you won't get the full DHW performance.

Okey-dokey. It is a tad noisy on speed 3. Is this normal for Wylo
pumps?

In CH mode, the boiler dies when the CH loop reaches 1.2k (just like
DHW mode) and it will re-fire at 2.3k. It only takes about 25 seconds
for the loop to reach 1.2k again, and shut off!

Better boilers can be instructed to not do full power for CH, they
also have anti-cycle delays that work.

This one has a potentiometer on the PCB which can be used to adjust
the burner gas pressure. The default is 'middle', and it can be
tweaked higher or lower. Maybe I should play with this?

My question, perhaps to all combi boiler owners: is this normal?

More or less for lower end kit.

Ah well. You get what you pay for, I suppose!

Should the CH loop get too hot when it's running on max DHW
temperature?

Yes if there is scaling and/or poor DHW flow.

The DHW flow can be very high (if the tap is fully open) so I think
that side it OK. I do wonder about the CH side, though...


Cheers,
Richard.

On Feb 16, 12:25 am, John Stumbles wrote:
On Thu, 15 Feb 2007 20:47:56 +0000, Ed Sirett wrote:

And is cycling inevitable once the rads are hot?

Maybe for this model.

This may be a stock fault (or feature?) for this model. I know of one
that does almost exactly what the OP is describing (for CH at least -
seems to be OK on DHW).

Hmm, interesting. Do you know if the DHW potentiometer also needs to
be backed away from maximum?

I'm wondering if I can improve the CH cycling by fitting a more
sophisticated room thermostat. Mine is a simple Honeywell analogue
device. Don't some of the digital models offer an anti-cycle?


Cheers,
Richard.

On Fri, 16 Feb 2007 11:22:07 -0800, Richard Walker wrote:

On Feb 15, 8:47 pm, Ed Sirett wrote:
On Thu, 15 Feb 2007 11:36:09 -0800, Richard Walker wrote:
Ed Wrote:
You now have a working boiler - the short cylcing on the CH is probably
the way it's made.

Perhaps, but the handbook says there is an anti-cycle function which
should stop re-firing for 2.5 minutes. It re-fires well within that
time. Mind you, perhaps it's just not very good!

Have you check whether the feature applies to the external control rather
than the internal themrostat? Simple turn the WALL thermostat down for a
few seconds and back up again and see how the system reacts.

I've just tried this, and the boiler does as soon as you reduce the
stat, then re-fires as soon as I turn it up! If I reduce the CH
potentiometer, the boiler simply cuts out sooner (at, say, 1.3k
instead of 1.2k resistance on the CH thermistor). Not much of an anti-
cycle, really!

The user manual claims that when the boiler reaches its set maximum
temperature (whatever that is!), it will not operate on heating for 3
minutes. The installer guide says 2.5 minutes!

I have backed the DHW temperature potentiometer off to about half-way,
and the DHW still comes out pretty hot.

Yes turn it lower if you provided that does not cause the burner to cycle.

OK. I've had it at just over half-way and ran gallons of hot water,
varying the flow every not and again. Not a single cut-out. If I put
the tap onto full flow, the water doesn't get quite so hot, but I
suppose that's because it's only a 24 kW combi.

Thing is, though... the user instructions say that the DHW
potentiometer should vary the water temp between 35 and 65 degrees C,
and that operating it on max is OK (the CH potentiometer should select
between 40 and 85 degrees C).

And should be left there, otherwise you won't get the full DHW performance.

Okey-dokey. It is a tad noisy on speed 3. Is this normal for Wylo
pumps?

In CH mode, the boiler dies when the CH loop reaches 1.2k (just like
DHW mode) and it will re-fire at 2.3k. It only takes about 25 seconds
for the loop to reach 1.2k again, and shut off!

Better boilers can be instructed to not do full power for CH, they
also have anti-cycle delays that work.

This one has a potentiometer on the PCB which can be used to adjust
the burner gas pressure. The default is 'middle', and it can be
tweaked higher or lower. Maybe I should play with this?

My question, perhaps to all combi boiler owners: is this normal?

More or less for lower end kit.

Ah well. You get what you pay for, I suppose!

Should the CH loop get too hot when it's running on max DHW
temperature?

Yes if there is scaling and/or poor DHW flow.

The DHW flow can be very high (if the tap is fully open) so I think
that side it OK. I do wonder about the CH side, though...


Sounds like it's doing everything it should except the anti-cycling delays.
How much do you trust the manual to be right? (Um...)
Where do you think the delay is implemented? (ON the PCB I'd guess).
Is there any adjustment for it? (Unlikely).

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Feb 17, 6:11 pm, wrote:
On 17 Feb,
Ed Sirett wrote:

Sounds like it's doing everything it should except the anti-cycling delays.
How much do you trust the manual to be right? (Um...)
Where do you think the delay is implemented? (ON the PCB I'd guess).
Is there any adjustment for it? (Unlikely).

Most likely an electrolytic capacitor on the pcb has dried out and lost
capacitance, reducing the delay to next to nothing.

Hmm, interesting. If I had a spare PCB, I'd probably risk replacing
every such capacitor and trying it. On my only one, though, I think
that's a step too far for me!

On Feb 17, 5:15 pm, Ed Sirett wrote:
On Fri, 16 Feb 2007 11:22:07 -0800, Richard Walker wrote:
On Feb 15, 8:47 pm, Ed Sirett wrote:
On Thu, 15 Feb 2007 11:36:09 -0800, Richard Walker wrote:

Should the CH loop get too hot when it's running on max DHW
temperature?

Yes if there is scaling and/or poor DHW flow.

The DHW flow can be very high (if the tap is fully open) so I think
that side it OK. I do wonder about the CH side, though...

Sounds like it's doing everything it should except the anti-cycling delays.

Yes, although I'm still concerned about having to back-off the DHW
temperature. It could all be connected to the short CH loop getting
too hot too quickly.

How much do you trust the manual to be right? (Um...)

Not much, to be honest. There seem to be several mistakes, and it
must be a poor translation from another language (Italian?).

Where do you think the delay is implemented? (ON the PCB I'd guess).

Yes, on the PCB.

Is there any adjustment for it? (Unlikely).

Nope, although there is a trimmer to adjust the max. flame used for
CH. I suppose I could turn this down a bit, but then the rads
wouldn't get nice and hot in ten minutes.

Also, the boiler has a room stat, but it's in a cold zone, so it
always calls for heat. I'm going to try getting a wireless one and
positioning it elsewhere. I guess that this might reduce the cycling.


Cheers,
Richard.