Hi all,

I've been lurking here for quite a while, but feel it's time to jump
in!

I've been in this house two and a half years, and for the last year my
Ravenheat RSF84ET boiler has been playing up. Now I know Ravenheat get
a slating all over the 'net, but this was working great, and I cannot
justify replacing the whole boiler when I'm not planning to hang around
in this house for much longer. It was fitted a few years ago, by the
previous owner (a spark who was training to be a plumber and gas
fitter). The whole house was re-plumbed and has modern radiators.

The central heating works very well. About a year ago, the hot water
started misbehaving. When opening a hot tap, the boiler senses, lights
on a low flame, increases to a full flame, provides hot water for
anything up to a minute, then clicks off. The flames vanish
completely. After a moment, it re-lights and the cycle begins again.

Initially, I found that lowering the DHW potentiometer to about two
thirds helped reduce chances of the problem occurring (although the
water still arrived to the tap piping hot). This doesn't happen every
time I use the DHW, but it does most times. Also, if the CH is on, it
is much less likely to happen.

A recommended Corgi engineer tried to sell me a brand new boiler
(1350ukp!) and finally decided that the gas valve wasn't modulating.
He reckoned it must be the gas valve or the PCB, but wasn't sure which
to replace!

I am 99% convinced by the gas valve not modulating theory, as when it
malfunctions, the flames are either max or min (nothing in-between).
However, I don't know if the PCB is telling the gas valve to switch
off, or the gas valve modulator is busted.

I put a multimeter across the two modulator terminals on the gas valve
(which connect to the PCB) and it reads anywhere between 0V (no flame),
3V (ignition flame) and 16V (full flame). Turning down the DHW
potentiometer reduces the max voltage slightly. From my crude
experimentation, the voltage seems to drop to 0, then the flames go
out, so I'm starting to wonder if the gas valve is OK and the PCB is
shot.

The same multimeter also shows me the resistances across the DHW and CH
potentiometers changing when I turn them. And the resistances across
the DHW and CH thermistors change as the pipes heat and cool.

Can anyone help with this? Does it sound as though I'm on the right
lines? Is there any way I can definitely work out if it is the gas
valve (which I'll have to get my Corgi to replace) or the PCB? (which I
can do) Or am I barking up the wrong tree completely?!


Many thanks,
Richard.
(apologies if Google Groups mangles this, but my post to alt.test came
out OK!)

In article . com,
Richard Walker writes

I've been in this house two and a half years, and for the last year my
Ravenheat RSF84ET boiler has been playing up. Now I know Ravenheat get
a slating all over the 'net, but this was working great, and I cannot
justify replacing the whole boiler when I'm not planning to hang around
in this house for much longer. It was fitted a few years ago, by the
previous owner (a spark who was training to be a plumber and gas
fitter). The whole house was re-plumbed and has modern radiators.

The central heating works very well. About a year ago, the hot water
started misbehaving. When opening a hot tap, the boiler senses, lights
on a low flame, increases to a full flame, provides hot water for
anything up to a minute, then clicks off. The flames vanish
completely. After a moment, it re-lights and the cycle begins again.

I am 99% convinced by the gas valve not modulating theory, as when it
malfunctions, the flames are either max or min (nothing in-between).
However, I don't know if the PCB is telling the gas valve to switch
off, or the gas valve modulator is busted.

I put a multimeter across the two modulator terminals on the gas valve
(which connect to the PCB) and it reads anywhere between 0V (no flame),
3V (ignition flame) and 16V (full flame). Turning down the DHW
potentiometer reduces the max voltage slightly. From my crude
experimentation, the voltage seems to drop to 0, then the flames go
out, so I'm starting to wonder if the gas valve is OK and the PCB is
shot.

The same multimeter also shows me the resistances across the DHW and CH
potentiometers changing when I turn them. And the resistances across
the DHW and CH thermistors change as the pipes heat and cool.

Can anyone help with this? Does it sound as though I'm on the right
lines? Is there any way I can definitely work out if it is the gas
valve (which I'll have to get my Corgi to replace) or the PCB? (which I
can do) Or am I barking up the wrong tree completely?!

Sounds like you're going about the fault finding in a logical manner but you
really need an installer manual, they're he
http://www.ravenheat.co.uk/Installationmanuals.htm
That should guide you through the process to narrow the fault down but the
varying voltage on the modulator coil suggest that the pcb is doing its job.
If it hasn't been looked at in a while then it may be needing a good service.
The flames are either max or min, do you know that it has
continuously variable modulation? I've just looked at a Vokera where it was
either min or max set by a solenoid coil on the gas valve and that was it,
crude but it is modulation.
--
fred
Plusnet - I hope you like vanilla

"Richard Walker" wrote in message
ups.com...
Hi all,

I've been lurking here for quite a while, but feel it's time to jump
in!

I've been in this house two and a half years, and for the last year my
Ravenheat RSF84ET boiler has been playing up. Now I know Ravenheat get
a slating all over the 'net, but this was working great, and I cannot
justify replacing the whole boiler when I'm not planning to hang around
in this house for much longer. It was fitted a few years ago, by the
previous owner (a spark who was training to be a plumber and gas
fitter). The whole house was re-plumbed and has modern radiators.

The central heating works very well. About a year ago, the hot water
started misbehaving. When opening a hot tap, the boiler senses, lights
on a low flame, increases to a full flame, provides hot water for
anything up to a minute, then clicks off. The flames vanish
completely. After a moment, it re-lights and the cycle begins again.

Initially, I found that lowering the DHW potentiometer to about two
thirds helped reduce chances of the problem occurring (although the
water still arrived to the tap piping hot). This doesn't happen every
time I use the DHW, but it does most times. Also, if the CH is on, it
is much less likely to happen.

A recommended Corgi engineer tried to sell me a brand new boiler
(1350ukp!) and finally decided that the gas valve wasn't modulating.
He reckoned it must be the gas valve or the PCB, but wasn't sure which
to replace!

I am 99% convinced by the gas valve not modulating theory, as when it
malfunctions, the flames are either max or min (nothing in-between).
However, I don't know if the PCB is telling the gas valve to switch
off, or the gas valve modulator is busted.

I put a multimeter across the two modulator terminals on the gas valve
(which connect to the PCB) and it reads anywhere between 0V (no flame),
3V (ignition flame) and 16V (full flame). Turning down the DHW
potentiometer reduces the max voltage slightly. From my crude
experimentation, the voltage seems to drop to 0, then the flames go
out, so I'm starting to wonder if the gas valve is OK and the PCB is
shot.

The same multimeter also shows me the resistances across the DHW and CH
potentiometers changing when I turn them. And the resistances across
the DHW and CH thermistors change as the pipes heat and cool.

Can anyone help with this? Does it sound as though I'm on the right
lines? Is there any way I can definitely work out if it is the gas
valve (which I'll have to get my Corgi to replace) or the PCB? (which I
can do) Or am I barking up the wrong tree completely?!


Many thanks,
Richard.
(apologies if Google Groups mangles this, but my post to alt.test came
out OK!)


Sounds like you're doing OK Richard. I can't fault your approach. My
Vaillant has an LCD diagnostic display, and one of the parameters you can
display is the gas valve current. Current mind you, not voltage, but if the
gas valve is essentially a resistive load then voltage and current should
vary proportionately.

When setting up my Vaillant combi in the beginning I had to measure the gas
pressures as modulated by the gas valve: I did this with a u-tube manometer,
and when I opened a hot tap ( there was one right next to the boiler, which
was convenient ) the gas pressure would shoot up to the maximum modulation
level for a short time then come down in a series of steps as the modulator
( which presumably sensed water flow ) adjusted itself to the flow of hot
water demanded. The valve current as displayed on the LCD varied in
sympathy.

This was a fairly rapid process, only a few seconds to modulate down.
You have determined that your gas valve operates, as it'll turn fully on or
fully off. You have also not seen much in the way of modulation from the
valve input voltage. I would have expected to see the input voltage to the
gas valve come down in a series of steps, especially if you varied the water
flow ( have you tried this? ).

So, your conclusion that its probably not the gas valve sounds correct.
Presumably after a minute at full chat, with insufficient water flow to
justify that heat output, either the DHW or the primary loop thermistor hit
their limits and cause a safety lockout. My Vaillant limits the DHW to 63C
max. It doesn't actually use the same thermistor to sense operating
temperature(?), only whether it exceeds 63C.

Its difficult to suggest how you might test this easily. Of course, if you
had the right kit you could unplug the gas valve input and operate it via a
variable voltage but that'd be a bit hairy unless you removed it from the
boiler. At the risk of getting the usual flak from safety first types, if a
variable resistor in the 0 - 5 kOhm region ( bit of a guess that, based on
your valve voltages and my gas valve currents ) were inserted inline with
the gas valve input, you could modulate the gas valve yourself by turning a
potentiometer ( configured as a variable resistor, i.e. using the central
terminal and one end terminal ) during the one minute periods when it goes
full on. Subject to not electrocuting yourself and not blowing anything up
of course! If the gas valve modulates when you twiddle the pot, then it the
pcb at fault, not the valve.

Fault-finding the pcb will be a thankless and impossible task unless
something is very obviously dead. Check for loose connections, blown fuses,
cracked solder joints ( they can be subtle ).

I would repeat your experiments with measuring the voltage to the gas valve,
and varying the DHW flow. If it doesn't modulate over at least half-a-dozen
steps then I guess its the pcb.

I suppose there is another possibility: when you demand full flow hot water
with the temperature dial at max, I imagine the gas valve will go to max
modulation at first. The question is, what method does the combi use to
determine when it needs to modulate down? Do the thermistors sense the delta
T between the rising main and the DHW and flag to the pcb when the required
temperature rise has been met? I'm not sure that it does work this way, but
my point is that if it did then the fault could be the inputs to the pcb
being wrong. The thermistors are probably standard ones, from a range ( try
YSI + thermistors in Google and you'll get a list that you can pick a
likely match from ). That way, you can check out your thermistors resistance
at cold ( probably 2200 Ohm ? ) and at hot and see if they're OK.
It still sounds like the pcb though.

Bit of a ramble, sorry,

Andy.

In message . com,
Richard Walker writes
Hi all,


A recommended Corgi engineer tried to sell me a brand new boiler
(1350ukp!) and finally decided that the gas valve wasn't modulating.
He reckoned it must be the gas valve or the PCB, but wasn't sure which
to replace!

Then he's a clueless ****** - it should be relatively straightforward
using a multimeter to find out whether it's the pcb or gas valve

sack him and get someone in who has a clue

--
geoff

Hi Fred,

Thanks for your comments.


fred wrote:

Sounds like you're going about the fault finding in a logical manner but you
really need an installer manual, they're he
http://www.ravenheat.co.uk/Installationmanuals.htm

I forgot to say: I did download and print the manual.
http://www.ravenheat.co.uk/pdf/RSF84/RSF841Print.pdf

The fault finding section is particularly poor. For my fault, It only
leads to 'check/replace DHW sensor'.

That should guide you through the process to narrow the fault down but the
varying voltage on the modulator coil suggest that the pcb is doing its job.

Yes, that's what I thought.

If it hasn't been looked at in a while then it may be needing a good service.

I don't think ever been looked at.

I'm terrified of 'a service' consisting of a wipe with a cloth, and a
100ukp bill.

The flames are either max or min, do you know that it has
continuously variable modulation? I've just looked at a Vokera where it was
either min or max set by a solenoid coil on the gas valve and that was it,
crude but it is modulation.

According to the manual, it can and should modulate.


Cheers,
Richard.

Hi Andy,

Andy wrote:

Sounds like you're doing OK Richard. I can't fault your approach.

Thanks.

When setting up my Vaillant combi in the beginning I had to measure the gas
pressures as modulated by the gas valve: I did this with a u-tube manometer,
and when I opened a hot tap ( there was one right next to the boiler, which
was convenient ) the gas pressure would shoot up to the maximum modulation
level for a short time then come down in a series of steps as the modulator
( which presumably sensed water flow ) adjusted itself to the flow of hot
water demanded. The valve current as displayed on the LCD varied in
sympathy.

Ah, yes. The Corgi engineer who had a look did something like this.
When I first explained the problem, he said the valve min/max was
probably set up incorrectly. After checking the valve and the
documentation, he said they were incorrect, so adjusted them to where
they should be. However, it still doesn't modulate correctly.

This was a fairly rapid process, only a few seconds to modulate down.
You have determined that your gas valve operates, as it'll turn fully on or
fully off. You have also not seen much in the way of modulation from the
valve input voltage. I would have expected to see the input voltage to the
gas valve come down in a series of steps, especially if you varied the water
flow ( have you tried this? ).

Yes. I tried the HW tap at various points between a trickle and a fire
hose.

The voltage measured did change: if the tap was fully open, the voltage
approx. 15 V, and if it was barely open it was more like 5V.

So, your conclusion that its probably not the gas valve sounds correct.
Presumably after a minute at full chat, with insufficient water flow to
justify that heat output, either the DHW or the primary loop thermistor hit
their limits and cause a safety lockout. My Vaillant limits the DHW to 63C
max. It doesn't actually use the same thermistor to sense operating
temperature(?), only whether it exceeds 63C.

That sounds feasible. Just before it clicks off, something makes a bit
of a 'puffing' noise - I think it's the fan going up a gear. Perhaps
because it's getting a bit too hot? A few seconds after the noise
starts, the flame is shut off completely.

Its difficult to suggest how you might test this easily. Of course, if you
had the right kit you could unplug the gas valve input and operate it via a
variable voltage but that'd be a bit hairy unless you removed it from the
boiler.

Hmm... That does sound iffy!

At the risk of getting the usual flak from safety first types, if a
variable resistor in the 0 - 5 kOhm region ( bit of a guess that, based on
your valve voltages and my gas valve currents ) were inserted inline with
the gas valve input, you could modulate the gas valve yourself by turning a
potentiometer ( configured as a variable resistor, i.e. using the central
terminal and one end terminal ) during the one minute periods when it goes
full on. Subject to not electrocuting yourself and not blowing anything up
of course! If the gas valve modulates when you twiddle the pot, then it the
pcb at fault, not the valve.

Now that's interesting. Has anyone done anything like this before? I
can't see it blowing up in my face, and it would only be a quick test.
It's not like I'd leave it wired up that way!

Fault-finding the pcb will be a thankless and impossible task unless
something is very obviously dead. Check for loose connections, blown fuses,
cracked solder joints ( they can be subtle ).

I was thinking that if I can find a cheap replacement PCB, then I could
always try it. Unfortunately, they are always rather expensive!

I would repeat your experiments with measuring the voltage to the gas valve,
and varying the DHW flow. If it doesn't modulate over at least half-a-dozen
steps then I guess its the pcb.

I did that before (probably didn't mention it in my post, though) and
the voltage does vary as I would expect. The thing I couldn't work out
is if the valve cuts out itself, or the PCB is telling it to cut out.
I suppose your potentiometer theory will help with this...

I suppose there is another possibility: when you demand full flow hot water
with the temperature dial at max, I imagine the gas valve will go to max
modulation at first.

Yes. However, If I unplug the two wires which go between the modulator
and PCB, then open the hot tap, the flames light (low) but never rise
to max.

The question is, what method does the combi use to
determine when it needs to modulate down? Do the thermistors sense the delta
T between the rising main and the DHW and flag to the pcb when the required
temperature rise has been met? I'm not sure that it does work this way, but
my point is that if it did then the fault could be the inputs to the pcb
being wrong. The thermistors are probably standard ones, from a range ( try
YSI + thermistors in Google and you'll get a list that you can pick a
likely match from ). That way, you can check out your thermistors resistance
at cold ( probably 2200 Ohm ? ) and at hot and see if they're OK.

There are thermistors sticking into the copper pipes for the HW output
and CH flow which are cabled back to the PCB, so I assume it monitors
them. Their resistance values appear to change as the pipes change in
temperature.

It still sounds like the pcb though.

Hmm. I'm edging towards trying to find a cheap replacement. In fact,
they seem like trivial microcontroller systems, so why on earth can't
we buy off-the-shelf generic ones which you program via a web page?! I
suppose I'd better not start on that!

Bit of a ramble, sorry,

No worries. I've realised that my post also looks like a ramble!


Cheers,
Richard.

raden wrote:

In message . com,
Richard Walker writes

A recommended Corgi engineer tried to sell me a brand new boiler
(1350ukp!) and finally decided that the gas valve wasn't modulating.
He reckoned it must be the gas valve or the PCB, but wasn't sure which
to replace!

Then he's a clueless ****** - it should be relatively straightforward
using a multimeter to find out whether it's the pcb or gas valve

sack him and get someone in who has a clue

I was wondering that myself...

I missed out the best bit: he visited in the morning, and I came back
from work at 17:30. The house smelled of gas! :-o

Turns out when he finished measuring the gas pressure at the valve, he
forgot to re-tighten the screw...

I'm terrified of picking someone at random, though. Any tips?


Cheers,
Richard.

On Fri, 01 Dec 2006 06:02:31 -0800, Richard Walker wrote:

raden wrote:

In message . com,
Richard Walker writes

A recommended Corgi engineer tried to sell me a brand new boiler
(1350ukp!) and finally decided that the gas valve wasn't modulating.
He reckoned it must be the gas valve or the PCB, but wasn't sure which
to replace!

Then he's a clueless ****** - it should be relatively straightforward
using a multimeter to find out whether it's the pcb or gas valve

sack him and get someone in who has a clue

I was wondering that myself...

I missed out the best bit: he visited in the morning, and I came back
from work at 17:30. The house smelled of gas! :-o

Turns out when he finished measuring the gas pressure at the valve, he
forgot to re-tighten the screw...

I'm terrified of picking someone at random, though. Any tips?

The voltages you measured are plausibly correct.

So if the flames are all or nothing then the GV modulator is shot.

There is invariably a 230V on/off GV in series with the low voltage
modulator.

--
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,


Ed Sirett wrote:

The voltages you measured are plausibly correct.

Hurrah!

So if the flames are all or nothing then the GV modulator is shot.

Yes, they are all or nothing.

However, the fault seems to be intermittent: sometimes it does work OK.
It seems to be getting worse, though.

There is invariably a 230V on/off GV in series with the low voltage
modulator.

I was wondering if the gas valve was itself no longer modulating, or
the PCB was for some reason (faulty itself, or a faulty sensor) telling
it to switch off. That's the bit that foxes me, and keeps me wondering
which part to replace!


Cheers,
Richard.

In message om,
Richard Walker writes
raden wrote:

In message . com,
Richard Walker writes

A recommended Corgi engineer tried to sell me a brand new boiler
(1350ukp!) and finally decided that the gas valve wasn't modulating.
He reckoned it must be the gas valve or the PCB, but wasn't sure which
to replace!

Then he's a clueless ****** - it should be relatively straightforward
using a multimeter to find out whether it's the pcb or gas valve

sack him and get someone in who has a clue

I was wondering that myself...

I missed out the best bit: he visited in the morning, and I came back
from work at 17:30. The house smelled of gas! :-o

Turns out when he finished measuring the gas pressure at the valve, he
forgot to re-tighten the screw...

I'm terrified of picking someone at random, though. Any tips?


Where are you?



Cheers,
Richard.


--
geoff

raden wrote:
In message om,
Richard Walker writes

I'm terrified of picking someone at random, though. Any tips?

Where are you?

TS20, Stockton-on-Tees (next to Middlesbrough).



Cheers,
Richard.

In message om,
Richard Walker writes

raden wrote:
In message om,
Richard Walker writes

I'm terrified of picking someone at random, though. Any tips?

Where are you?

TS20, Stockton-on-Tees (next to Middlesbrough).

Nobody springs immediately to mind

Ring me on Monday, I'll look in my customer database

01923 229224

--
geoff

On Fri, 01 Dec 2006 11:14:06 -0800, Richard Walker wrote:

Hi Ed,


Ed Sirett wrote:

The voltages you measured are plausibly correct.

Hurrah!

So if the flames are all or nothing then the GV modulator is shot.

Yes, they are all or nothing.

However, the fault seems to be intermittent: sometimes it does work OK.
It seems to be getting worse, though.

There is invariably a 230V on/off GV in series with the low voltage
modulator.

I was wondering if the gas valve was itself no longer modulating, or
the PCB was for some reason (faulty itself, or a faulty sensor) telling
it to switch off. That's the bit that foxes me, and keeps me wondering
which part to replace!


Can you measure the voltages when it's misbehaving? That would track it
down to the GV if the voltages are OK and the PCB if they are not.




--
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

Ed Sirett wrote:
On Fri, 01 Dec 2006 11:14:06 -0800, Richard Walker wrote:

Ed Sirett wrote:

There is invariably a 230V on/off GV in series with the low voltage
modulator.

I was wondering if the gas valve was itself no longer modulating, or
the PCB was for some reason (faulty itself, or a faulty sensor) telling
it to switch off. That's the bit that foxes me, and keeps me wondering
which part to replace!

Can you measure the voltages when it's misbehaving? That would track it
down to the GV if the voltages are OK and the PCB if they are not.

I've had a quick play and, for the HW, the usual sequence is:

1) tap closed, 0V across modulator
2) tap opened, 3V across modulator (low flame)
3) few seconds later, 15V across modulator (high flame)
4) up to a minute later, flame dies and modulator drops down to 0V
(this is the fault)
5) pause, then 3V across modulator (low flame)
6) go to (3)

I tried measuring the voltage with only the CH on (as the problem seems
to be limited to the HW). Interestingly, the CH seems to use either a
very low voltage (sub-0.5V) when it first starts, then shoots up to 10V
to heat the water, then clicks off (0V) when the thermostat is happy.
Therefore, I assume the problem lies with the modulator in the 0-10V
range, which is why it doesn't show up with the CH.

Going back to the HW, if I open the tap fully, the voltage stays at
15V. If I back-off the flow slightly (so it's not acting like a water
cannon!) then the voltage reduces slightly (say, to 12V) but then the
flames die completely.

This is all starting to convince me that it's the gas valve - or more
specifically, the modulator.


Cheers,
Richard.

On Sat, 02 Dec 2006 15:09:07 -0800, Richard Walker wrote:

Ed Sirett wrote:
On Fri, 01 Dec 2006 11:14:06 -0800, Richard Walker wrote:

Ed Sirett wrote:

There is invariably a 230V on/off GV in series with the low voltage
modulator.

I was wondering if the gas valve was itself no longer modulating, or
the PCB was for some reason (faulty itself, or a faulty sensor) telling
it to switch off. That's the bit that foxes me, and keeps me wondering
which part to replace!

Can you measure the voltages when it's misbehaving? That would track it
down to the GV if the voltages are OK and the PCB if they are not.

I've had a quick play and, for the HW, the usual sequence is:

1) tap closed, 0V across modulator
2) tap opened, 3V across modulator (low flame)
3) few seconds later, 15V across modulator (high flame)
4) up to a minute later, flame dies and modulator drops down to 0V
(this is the fault)
5) pause, then 3V across modulator (low flame)
6) go to (3)

I tried measuring the voltage with only the CH on (as the problem seems
to be limited to the HW). Interestingly, the CH seems to use either a
very low voltage (sub-0.5V) when it first starts, then shoots up to 10V
to heat the water, then clicks off (0V) when the thermostat is happy.
Therefore, I assume the problem lies with the modulator in the 0-10V
range, which is why it doesn't show up with the CH.

Going back to the HW, if I open the tap fully, the voltage stays at
15V. If I back-off the flow slightly (so it's not acting like a water
cannon!) then the voltage reduces slightly (say, to 12V) but then the
flames die completely.

This is all starting to convince me that it's the gas valve - or more
specifically, the modulator.


This does sound like the correct operation of both the GV and PCB!
The problem seems to be that the PCB does all or nothing.

This could be a PCB problem but I'm also wondering if there might be a
problem with something else.

When you say "the thermostat" for the CH do you mean the wall thermostat.
In which case could you try a lower heat setting on the boiler and a
higher heat setting on the wall. This should make the boiler modulate for
CH when the return water warms up.

The way the modulator works, I _think_ is as follows:
The gas valve can vary the burner pressure between two fixed
mechanically preset settings. On the ones I've investigated the 'default'
setting is the lowest pressure which is the ignition rate. As the DC
voltage (and so current) is increased on the modulator the gas pressure
will increase to the maximum. One model I know for sure about is in the
range 0-9V, but it may be that other models use other voltage ranges?

A recon PCB won't cost you much more than a one visit call by a pro.
You will need to follow the book and that almost certainly means checking
gas burner pressures so you need to be able to do that, competently.


--
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

In article . com,
Richard Walker writes
Ed Sirett wrote:
On Fri, 01 Dec 2006 11:14:06 -0800, Richard Walker wrote:

Ed Sirett wrote:

There is invariably a 230V on/off GV in series with the low voltage
modulator.

I was wondering if the gas valve was itself no longer modulating, or
the PCB was for some reason (faulty itself, or a faulty sensor) telling
it to switch off. That's the bit that foxes me, and keeps me wondering
which part to replace!

Can you measure the voltages when it's misbehaving? That would track it
down to the GV if the voltages are OK and the PCB if they are not.

I've had a quick play and, for the HW, the usual sequence is:

1) tap closed, 0V across modulator
2) tap opened, 3V across modulator (low flame)
3) few seconds later, 15V across modulator (high flame)
4) up to a minute later, flame dies and modulator drops down to 0V
(this is the fault)
5) pause, then 3V across modulator (low flame)
6) go to (3)

I tried measuring the voltage with only the CH on (as the problem seems
to be limited to the HW). Interestingly, the CH seems to use either a
very low voltage (sub-0.5V) when it first starts, then shoots up to 10V
to heat the water, then clicks off (0V) when the thermostat is happy.
Therefore, I assume the problem lies with the modulator in the 0-10V
range, which is why it doesn't show up with the CH.

Going back to the HW, if I open the tap fully, the voltage stays at
15V. If I back-off the flow slightly (so it's not acting like a water
cannon!) then the voltage reduces slightly (say, to 12V) but then the
flames die completely.

This is all starting to convince me that it's the gas valve - or more
specifically, the modulator.

Ok, take the pcb out of the loop, feed the modulator coil from a variable
power supply and see if the flame varies with the applied voltage. If it
doesn't then it's the gas valve (modulator). The modulator may be a plunger
operated by a coil so it may be possible to remove that part and check
that it is not sticking.

I have seen a similar problem but in that case the modulator coil was
operating the plunger correctly but the minimum gas rate had been over-
set meaning that the flame didn't reduce and so the control would sense
an over-temp and kill the flame. As you mention 3V and low flame I
assume you are able to achieve low flame at some point so this is not your
problem.
--
fred
Plusnet - I hope you like vanilla

fred wrote:
In article . com,
Richard Walker writes

Going back to the HW, if I open the tap fully, the voltage stays at
15V. If I back-off the flow slightly (so it's not acting like a water
cannon!) then the voltage reduces slightly (say, to 12V) but then the
flames die completely.

This is all starting to convince me that it's the gas valve - or more
specifically, the modulator.

Ok, take the pcb out of the loop, feed the modulator coil from a variable
power supply and see if the flame varies with the applied voltage. If it
doesn't then it's the gas valve (modulator). The modulator may be a plunger
operated by a coil so it may be possible to remove that part and check
that it is not sticking.

I tried putting a potentiometer in-between the gas valve modulator and
PCB, as Andy suggested earlier. I was hoping that once it goes to 15V
(full flame) I could wind the pot and see the voltage (and perhaps
flame) reduce.

Unfortunately, turning the pot resulted in a small decrease in voltage
(and large decrease in flame), then the voltage according to the
multimeter started rocketing up to 30+V. Not quite sure what happened
there - maybe I didn't connect up the pot properly?

I was a bit too scared to try a variable power supply directly in place
of the PCB, but I might build up the courage to give it a go!

I have seen a similar problem but in that case the modulator coil was
operating the plunger correctly but the minimum gas rate had been over-
set meaning that the flame didn't reduce and so the control would sense
an over-temp and kill the flame. As you mention 3V and low flame I
assume you are able to achieve low flame at some point so this is not your
problem.

Interestingly, when the Corgi bloke first looked at it, he said one of
the settings (can't remember if it was min or max, I think max) was too
high. He corrected it, but it didn't fix the problem.


Cheers,
Richard.

Ed Sirett wrote:
On Sat, 02 Dec 2006 15:09:07 -0800, Richard Walker wrote:

Going back to the HW, if I open the tap fully, the voltage stays at
15V. If I back-off the flow slightly (so it's not acting like a water
cannon!) then the voltage reduces slightly (say, to 12V) but then the
flames die completely.

This is all starting to convince me that it's the gas valve - or more
specifically, the modulator.

This does sound like the correct operation of both the GV and PCB!

Aarrgghh!

The problem seems to be that the PCB does all or nothing.
This could be a PCB problem but I'm also wondering if there might be a
problem with something else.

Hmm. I was wondering if perhaps a sensor is screaming 'too much' or
'error' at the PCB which is what makes it switch off.

When you say "the thermostat" for the CH do you mean the wall thermostat.

Yes. To make the CH click off, I simply reduced it down to the lowest
setting. And then to make it come on again, I whacked it up to max.

In which case could you try a lower heat setting on the boiler and a
higher heat setting on the wall. This should make the boiler modulate for
CH when the return water warms up.

I'll give this a whirl and report back.

The way the modulator works, I _think_ is as follows:
The gas valve can vary the burner pressure between two fixed
mechanically preset settings. On the ones I've investigated the 'default'
setting is the lowest pressure which is the ignition rate. As the DC
voltage (and so current) is increased on the modulator the gas pressure
will increase to the maximum.

Makes sense.

One model I know for sure about is in the
range 0-9V, but it may be that other models use other voltage ranges?

The GV modulator carries a sticker: max 28V, 165 mA (range 3-37 mbar).
It claims to be a Honeywell VK4100M.

A recon PCB won't cost you much more than a one visit call by a pro.
You will need to follow the book and that almost certainly means checking
gas burner pressures so you need to be able to do that, competently.

I'd confidently change the PCB, as it looks no harder than changing the
timeclock (which didn't work when I first moved in). According to the
Corgi guy who looked at it last week, the min/max pressure at the GV is
set correctly.

If I could find a cheap PCB, I'd try it!


Cheers,
Richard.

On Mon, 04 Dec 2006 13:49:34 -0800, Richard Walker wrote:

Ed Sirett wrote:
On Sat, 02 Dec 2006 15:09:07 -0800, Richard Walker wrote:

Going back to the HW, if I open the tap fully, the voltage stays at
15V. If I back-off the flow slightly (so it's not acting like a water
cannon!) then the voltage reduces slightly (say, to 12V) but then the
flames die completely.

This is all starting to convince me that it's the gas valve - or more
specifically, the modulator.

This does sound like the correct operation of both the GV and PCB!

Aarrgghh!

The problem seems to be that the PCB does all or nothing.
This could be a PCB problem but I'm also wondering if there might be a
problem with something else.

Hmm. I was wondering if perhaps a sensor is screaming 'too much' or
'error' at the PCB which is what makes it switch off.

When you say "the thermostat" for the CH do you mean the wall thermostat.

Yes. To make the CH click off, I simply reduced it down to the lowest
setting. And then to make it come on again, I whacked it up to max.

In which case could you try a lower heat setting on the boiler and a
higher heat setting on the wall. This should make the boiler modulate for
CH when the return water warms up.

I'll give this a whirl and report back.

The way the modulator works, I _think_ is as follows:
The gas valve can vary the burner pressure between two fixed
mechanically preset settings. On the ones I've investigated the 'default'
setting is the lowest pressure which is the ignition rate. As the DC
voltage (and so current) is increased on the modulator the gas pressure
will increase to the maximum.

Makes sense.

One model I know for sure about is in the
range 0-9V, but it may be that other models use other voltage ranges?

The GV modulator carries a sticker: max 28V, 165 mA (range 3-37 mbar).
It claims to be a Honeywell VK4100M.

A recon PCB won't cost you much more than a one visit call by a pro.
You will need to follow the book and that almost certainly means checking
gas burner pressures so you need to be able to do that, competently.

I'd confidently change the PCB, as it looks no harder than changing the
timeclock (which didn't work when I first moved in). According to the
Corgi guy who looked at it last week, the min/max pressure at the GV is
set correctly.

If I could find a cheap PCB, I'd try it!

Check the part number. See if the one listed on the CETLTD web site is
suitable. £35+Carriage+VAT.


--
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

In message , Ed Sirett
writes

A recon PCB won't cost you much more than a one visit call by a pro.
You will need to follow the book and that almost certainly means checking
gas burner pressures so you need to be able to do that, competently.

I'd confidently change the PCB, as it looks no harder than changing the
timeclock (which didn't work when I first moved in). According to the
Corgi guy who looked at it last week, the min/max pressure at the GV is
set correctly.

If I could find a cheap PCB, I'd try it!

Check the part number. See if the one listed on the CETLTD web site is
suitable. £35+Carriage+VAT.


I've been keeping quiet here ...

I don't do them ATM

--
geoff

Richard Walker wrote:
Ed Sirett wrote:
In which case could you try a lower heat setting on the boiler and a
higher heat setting on the wall. This should make the boiler modulate for
CH when the return water warms up.

I'll give this a whirl and report back.

I lowered the CH potentiometer to a very low setting, put the
thermostat onto max, and switched on the CH. The pump started, but the
boiler didn't fire. Perhaps this could have been because the heating
had been on previously?

I tried again with a slightly higher temperature on the pot, and the
boiler lit. From my basic measurements and twiddling the pot a touch,
it seemed that the flame varied slightly as did the voltage across the
modulator. Perhaps the GV modulator is OK?

As a random flash of inspiration, I also tried unplugging the HW
thermistor (thinking that perhaps it was reporting the HW system being
too hot and shutting down) and trying a hot tap. Same hot/cold cycling
problem, and no modulation. Ah well.

I think I need an expert to take a look!


Cheers,
Richard.

Hi Geoff,

raden wrote:
In message om,
Richard Walker writes
raden wrote:
In message om,
Richard Walker writes

I'm terrified of picking someone at random, though. Any tips?

Where are you?

TS20, Stockton-on-Tees (next to Middlesbrough).

Nobody springs immediately to mind

Ring me on Monday, I'll look in my customer database

01923 229224

Sorry for the delay - I'll try and do this tomorrow. I've been meaning
to ring for the last two days, but never remembered at a quiet moment!
Maybe I need to relax more at work?!


Cheers,
Richard.

In message . com,
Richard Walker writes
Hi Geoff,

raden wrote:
In message om,
Richard Walker writes
raden wrote:
In message om,
Richard Walker writes

I'm terrified of picking someone at random, though. Any tips?

Where are you?

TS20, Stockton-on-Tees (next to Middlesbrough).

Nobody springs immediately to mind

Ring me on Monday, I'll look in my customer database

01923 229224

Sorry for the delay - I'll try and do this tomorrow. I've been meaning
to ring for the last two days, but never remembered at a quiet moment!
Maybe I need to relax more at work?!

Well, with my main printer down, it's not been much of a "put the feet
up day" for me either

--
geoff

In article . com,
Richard Walker writes

fred wrote:
In article . com,
Richard Walker writes


Ok, take the pcb out of the loop, feed the modulator coil from a variable
power supply and see if the flame varies with the applied voltage. If it
doesn't then it's the gas valve (modulator). The modulator may be a plunger
operated by a coil so it may be possible to remove that part and check
that it is not sticking.

I tried putting a potentiometer in-between the gas valve modulator and
PCB, as Andy suggested earlier. I was hoping that once it goes to 15V
(full flame) I could wind the pot and see the voltage (and perhaps
flame) reduce.

The only problem there is that you haven't eliminated one of the (two)
possible fault causes so you can't narrow down the fault.

Unfortunately, turning the pot resulted in a small decrease in voltage
(and large decrease in flame), then the voltage according to the
multimeter started rocketing up to 30+V. Not quite sure what happened
there - maybe I didn't connect up the pot properly?

I was a bit too scared to try a variable power supply directly in place
of the PCB, but I might build up the courage to give it a go!

If it is just a solenoid coil then there is little that you can do to damage it
so give it a try, it may give you the info you need. You'll likely be going far
deeper into the fault finding process that a random bloke pulled from the
yellow pages.

I have seen a similar problem but in that case the modulator coil was
operating the plunger correctly but the minimum gas rate had been over-
set meaning that the flame didn't reduce and so the control would sense
an over-temp and kill the flame. As you mention 3V and low flame I
assume you are able to achieve low flame at some point so this is not your
problem.

Interestingly, when the Corgi bloke first looked at it, he said one of
the settings (can't remember if it was min or max, I think max) was too
high. He corrected it, but it didn't fix the problem.

Minimum rate set ridiculously high would give the symptoms you describe.
I'm just wondering if the gas valve would give you minimum rate with the
mod coil connections disconnected, letting you see it run at minimum rate.
The variable supply would let you see it run at all levels though.

Good luck.
--
fred
Plusnet - I hope you like vanilla

On Tue, 05 Dec 2006 13:09:35 -0800, Richard Walker wrote:

Richard Walker wrote:
Ed Sirett wrote:
In which case could you try a lower heat setting on the boiler and a
higher heat setting on the wall. This should make the boiler modulate for
CH when the return water warms up.

I'll give this a whirl and report back.

I lowered the CH potentiometer to a very low setting, put the
thermostat onto max, and switched on the CH. The pump started, but the
boiler didn't fire. Perhaps this could have been because the heating
had been on previously?

I tried again with a slightly higher temperature on the pot, and the
boiler lit. From my basic measurements and twiddling the pot a touch,
it seemed that the flame varied slightly as did the voltage across the
modulator. Perhaps the GV modulator is OK?

If you can see a difference in the flame then the modulator is working
well. I'd say the GV is in the clear.


As a random flash of inspiration, I also tried unplugging the HW
thermistor (thinking that perhaps it was reporting the HW system being
too hot and shutting down) and trying a hot tap. Same hot/cold cycling
problem, and no modulation. Ah well.

I think I need an expert to take a look!


Cheers,
Richard.

Is the H/C cycling only happening for HW? In which case the most likely
case is that the secondary heat exchanger is scaled up. Not only does the
chalk patina in the 2ndHX reduce the maximum heat transfer to the DHW but
it tends to add a delay in the feedback system causing the burner power to
oscillate or at least become less stable.

--
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

In message . com,
Richard Walker writes
Hi Geoff,

raden wrote:
In message om,
Richard Walker writes
raden wrote:
In message om,
Richard Walker writes

I'm terrified of picking someone at random, though. Any tips?

Where are you?

TS20, Stockton-on-Tees (next to Middlesbrough).

Nobody springs immediately to mind

Ring me on Monday, I'll look in my customer database

01923 229224

Sorry for the delay - I'll try and do this tomorrow. I've been meaning
to ring for the last two days, but never remembered at a quiet moment!
Maybe I need to relax more at work?!

Right - printers installed an' all

try again


--
geoff

Hi Fred,

fred wrote:

In article . com,
Richard Walker writes

[ testing modulating part of gas valve ]

I was a bit too scared to try a variable power supply directly in place
of the PCB, but I might build up the courage to give it a go!

If it is just a solenoid coil then there is little that you can do to damage it
so give it a try, it may give you the info you need. You'll likely be going far
deeper into the fault finding process that a random bloke pulled from the
yellow pages.

OK, I've finally managed to pluck up the courage and borrow a variable
PSU!

I set the PSU to 3V and opened the HW tap. The boiler fired up with a
low flame (as it usually would). After a few seconds, I increased the
voltage to approx. 15 V and saw some nice high flames.

After a minute or so, there was the small air-sort-of-hissing (fan?)
sound which would usually be followed by the flame dying. Instead of
waiting for this to happen, I reduced the voltage slightly, and the
flame stayed. The hot water supply seemed consistent!

I repeated this a number of times, and also discovered that if I
ignored the air-hissing sound and left the PSU on 15 V anyway, then the
flame would die. I assume, therefore, that another part of the
electronics is shutting off the power to the entire GV.

Question is... is it a sensor which is telling the PCB that something
isn't right, or is the PCB bust?


Cheers,
Richard.

Ed Sirett wrote:

On Tue, 05 Dec 2006 13:09:35 -0800, Richard Walker wrote:

I tried again with a slightly higher temperature on the pot, and the
boiler lit. From my basic measurements and twiddling the pot a touch,
it seemed that the flame varied slightly as did the voltage across the
modulator. Perhaps the GV modulator is OK?

If you can see a difference in the flame then the modulator is working
well. I'd say the GV is in the clear.

Yes, after my experiments with the variable PSU and the CH, I'm
starting to think that the GV is OK.

Question is... is the PCB doing strange things, or is one of the
attached sensors playing up?! Or both?!

Is the H/C cycling only happening for HW? In which case the most likely
case is that the secondary heat exchanger is scaled up. Not only does the
chalk patina in the 2ndHX reduce the maximum heat transfer to the DHW but
it tends to add a delay in the feedback system causing the burner power to
oscillate or at least become less stable.

Yes, it's only HW which cycles H/C.

When it does this, there are times when it's piping hot (almost too hot
to put your hand under) and of course, times when it's almost
mains-water-cold!

Is scaling a problem all over the UK? I ask because I'm in an area
where the water is plentiful and very soft. Limescale and that soapy
feeling in water is something I only experience when away from home!



Cheers,
Richard.

Richard Walker wrote:

Question is... is the PCB doing strange things, or is one of the
attached sensors playing up?! Or both?!

Bad form to follow-up my own, I know, but I thought I'd share the
following with the group, in case it helps anyone else in futu

Thanks to the encouragement of the thread contributors, I decided to
extend my experimentation. I tried replacing the DHW and CH
thermistors with a few different fixed resistors (assuming they are
typical 10 KOhm at 25 degC jobbies). With a 3K resistor in place of
the CH thermistor, I was able to get the boiler to run quite well, and
even modulate slightly (although I think it was starting to get a bit
too hot!).

After talking to Ravenheat's sales line (the technical one was only for
Corgis), they informed me that the 'wet' (in-line) thermistors were
obsoleted in 2005 and replaced by clip-on 'dry' types. I suspect that
the wet ones eventually rot!

Anyway, I've just replaced the CH thermistor with one of the clip-on
types, and after a few tests, the boiler is back to its old self! A
decent rate of hot water on demand - hurrah! I can't believe that I've
lived with it for a year when it was so simple! I won't quite relax
until it's worked consistently for a few days, mind you.

So, all fixed for 15ukp in parts. The original Corgi guy who quoted me
for the new boiler still hasn't phoned back...


Cheers,
Richard.