All,

still looking for a little help with my boiler which has been making
noises or the last 18 months (since I bought house).

A bit of background...

The system is a fully pumped CH and HW system with a motorised valve,
cylinder stat, 1 room stat. there is a bypass from pipe from the pump
back to the inlet of the boiler with a gate valve (what is this
for?????)There are 9 rads 2 of which are fitted as bypass devices
(shower room and bathroom). Bolier is wall moutned on first floor in
an airing cupboard right next to HW tank.

The boiler is a Thorn EMI Apollo Fanfare 30/50i fitted in 1987 when
house built
In the last 12 months I have replaced the pump with a suitable
Grundfos Alpha repalcement, tried to descale the system and replaced
the auto air vent on top of the boiler. I have also tried to make
sure that the system is properly vented but I am not really sure if I
have achieved this. The noise has improved but not drastically - in
fact the way the boiler behaves seems slightly changeable so it is
possible that all my efforts are in vain.

The symptom...

On switching on (firing up) from cold everything works OK for few
minutes. Then I get massive bangs that wake the
dead/neighbours/neighbours dogs. Then system settles down after 1-4
iterations of the start-bang-stop cycle. Having gone into the loft to
investigate I can see gas (I am pretty sure steam) bubbling/exploding
out of the CH header tank during the banging - there is not a safety
vent pipe above the tank as I have seen in other installs. The steam
appears to be coming into the tank via the outlet that feeds water
from the header tank to the main system.

Recently I have come of the opinion that the pump is switching off for
perhaps 20 seconds (there is a green LED which shows pump is running)
- the water in the boiler really does boil, steam evolves and the
expansion forces it to the header tank - then the pump kicks back in
again for no real reason (green light comes on) and unless the cycle
is repeated everything settles down. Immediately after the bang there
is a real whooshing sound in the pipes which I presume is the sound of
tiny gas (steam) bubbles being circulated this soon settles and is not
present in normal operation.

So I guess my line of questioning should be around the control logic
which switches the pump on/off.

I know the boiler has a lo stat, high stat and an overrun stat - you
can see these on the pipes when the covers are off. The overrun seems
to work as the pump will keep operating (with light on) for some time
after boiler has stopped heating. With the lo stat selected the
bolier never really seems to get going jut starts, does a little
banging and stops... In the High position this is the only thing that
seems to kickstart the boiler and get it going - as I say once the
banging is over in normal operation the boiler/pump work fine.

So - how does the logic work which switches the pump on/off?

Would faulty stat(s) cause these symptoms? I could understand if a
stat failed that the pump might stay on for ever or never come on but
why does it come on, go off for a bit (20 seconds) and then come back
on as the boiler is boling and making a racket...

Can the pump switch itself off or is it, as I believe, a fairly dumb
device which lights up and spins when it has power and switches off
when there is no power.

What else could be causing this pump behaviour and then boiler noise(I
am sure it is not loose connection etc. fault is too consistent) can
the pump itself shutoff???

I am really desperate to try and fix this as I do not think there is
necessarily anything wrong with the boiler and do not want to try and
find £1500 for a new one. I am also reluctant to spend lots on fernox
etc until I know bolier is not about to end up in landfill.

SOrry for long post but I tried to give detail. If there are any
questions/suggestions please let me know and I will try them. I have
a wife and baby who are getting increasingly unhappy with me for this


Thanks in advance
Tim

On 26 Oct 2004 05:32:40 -0700, (Tim) wrote:

All,
(SNIP)
Thanks in advance
Tim

I am DIY.
I hate expensive plumbers.
TURN IT OFF NOW!
Call a plumber!

The banging is caused, as you seem to know, by the lack of flow through the
boiler, causing the pint or so of water actually in the boiler to turn to
steam. I would imagine the bang is when the steam suddenly condenses when
it hits the cooler water.

As for the pump, they are in fact dumb, and should not turn on and off on
their own. The boiler electronics may turn them on/off, or they will be on
for the entire duration of the "CH on" cycle. Not that I have much
experience, but I would have thought a broken pump would either work or not
work (I have had one get weaker), so maybe the on/off action is caused by a
loose wire. Maybe the system heating up moves the loose connection via
thermal expansion, causing it to stop for a while.

I would check the wires are secure (waggling them while on would cause a cut
out of the pump). Failing that, I would fit a new pump (about £30-40). My
pump in the last house had a valve each side of it, making it easy to swap
without draining the whole system.

You may need a tool to turn the pump head around (by removing 4 allen
bolts). The pump must pump in a certain direction, but to make wiring
easier, you can turn the pump head around so the junction box is accessible.
You may be lucky and buy a pump that is the right way around though.

Bob

On Tue, 26 Oct 2004 05:32:40 -0700, Tim wrote:

snip

The type of temperature sensors you have in the boiler are apt to drift
way out of calibration over the years. So it is possible that either the
high or low setting are not around 65C and 80C as they should be.

There is an over heat sensor (95C) which also ought to have responded to the
boiling? However if there were no flow at all it is _just_ possible that the
steam is being raised in the heat exchanger and never gets to the o/h
stat.

The pump over-run stat is meant to keep the pump running at all times when
the boiler is on and at any time the boiler is above a certain temp until
the boiler cools down. It will only work if the boiler is correctly wired
with both switched and permanent lives and the pump is connected to the
boiler and not in parallel with the switched live of the boiler.

Now any or all of the above 4 'cans' can and do cause problmes with this
model.

I don't know a geat deal about Grundfos Alphas. I do know that the idea of
reducing the circulation effort as the system warms up has got to be bad
news, unless the burner is turned down by the same control (as is the case
in many modern boilers). In particular it sounds like the Alpha also tries
periods of not pumping - that might work on a cast iron lump boiler but
it's really bad news on a low water content boiler like yours.

I'd first replace the Alpha with a bog standard £30 pump.
Then you will be able to diagnose the problems with the temperture sensors
if any.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at 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

Thanks for the reply Ed,
Comments in line, anyone please feel free to chip in...

The type of temperature sensors you have in the boiler are apt to drift
way out of calibration over the years. So it is possible that either the
high or low setting are not around 65C and 80C as they should be.

This is what I had thought. If one or more of the stats are out, I
wonder if it could be responsible for the behviour of the pump though.
I dont think any boiling occurs before the pump stops - as I say the
green LED on the pump goes out so I am sure that the boiler has
stopped feeding current to the pump by this stage.
This does not explain why the pump comes on to start with...if there
was a flowchart which showed how/when the pump got power it would help

Is there some sort of cold running override which turns the pump on
when the system starts up??? If you think about it there must be
something which achieves this or otherwise the pump would not start
until a threshold value had ben reached by one of the stats...

There is an over heat sensor (95C) which also ought to have responded to the
boiling? However if there were no flow at all it is _just_ possible that the
steam is being raised in the heat exchanger and never gets to the o/h
stat.

Perhaps it is this sensor which kicks in ad restarts the pump??? If
this has creeped to about 100 then you ould imagine the water will
boil and then the overheat kicks the pump off again
Again this does not explain why the pump comes on to start with - see
cold start theory above

The pump over-run stat is meant to keep the pump running at all times when
the boiler is on and at any time the boiler is above a certain temp until
the boiler cools down. It will only work if the boiler is correctly wired
with both switched and permanent lives and the pump is connected to the
boiler and not in parallel with the switched live of the boiler.

This *seems* to work fine from an overrun point of view - sounds like
boiler wis wired right...

Now any or all of the above 4 'cans' can and do cause problmes with this
model.



I don't know a geat deal about Grundfos Alphas. I do know that the idea of
reducing the circulation effort as the system warms up has got to be bad
news, unless the burner is turned down by the same control (as is the case
in many modern boilers). In particular it sounds like the Alpha also tries
periods of not pumping - that might work on a cast iron lump boiler but
it's really bad news on a low water content boiler like yours.

OK well I have been running the alpha in dumb mode on the old
fashioned 1,2,3 positions - in this mode it does not try and do
anything clever. So I think changing to another pump is something I
will not try yet...I will put a multimeter across the pump tonight and
see if, when it stops, it is being fed current (ie is the pump
switching itself off or is the boiler doing it)

I'd first replace the Alpha with a bog standard £30 pump.
Then you will be able to diagnose the problems with the temperture sensors
if any.


I think the position 1,2,3 trick will suffice here, but if I am wrong
someone please correct me.


So does anyone know either how I can test the stats and where I can
buy replacements and for how much??? Are the stats failry generic
parts or are they bespoke per manufacturer and boiler???

Thanks
Tim

On Wed, 27 Oct 2004 04:50:33 -0700, Tim wrote:

snip
I had not realized the Alpha could emulate dumb modes so that is
worthwhile, certainly any mode which turns the pump off even though power
is applied is going to cause problems.

The over-heat stat if it operates should have shut the boiler down
requiring manual intervention to restart.
On the old permanent pilots it simply killed the thermocouple circuit and
the gas valve dropped out.
However yours maybe an electronic ignition model?

The over-run stat works like this: The pump is connected to the common
pole of the thermostat. When cold the over-run stat connects the switched
lived to the pump when hot the permanent live is connected to the pump.

A failure mode of these devices is that a 'dead zone' can emerge between
the cold and hot states leaving the pump completely unpowered at certain
temperatures.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at 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

Thanks again Ed,

snip
I had not realized the Alpha could emulate dumb modes so that is
worthwhile, certainly any mode which turns the pump off even though power
is applied is going to cause problems.

agreed, I have tested and power is definitely not being delivered to
the pump for a short period between hot and boiling...it then comes
back in when the boiling has happened.

The over-heat stat if it operates should have shut the boiler down
requiring manual intervention to restart.
On the old permanent pilots it simply killed the thermocouple circuit and
the gas valve dropped out.
However yours maybe an electronic ignition model?


It is elec ignition, interestingly sometimes it fails differently - I
am guessing here that if the pump does not kick back in the overheat
stat shuts down the boiler and then we start again... starting to make
sense now.

The over-run stat works like this: The pump is connected to the common
pole of the thermostat. When cold the over-run stat connects the switched
lived to the pump when hot the permanent live is connected to the pump.

which gives the kind of cold start functionality I ws thinking of (all
be it achieved in a far more straight forward way...)

A failure mode of these devices is that a 'dead zone' can emerge between
the cold and hot states leaving the pump completely unpowered at certain
temperatures.

That sounds exactly like the problem...so all I need to do is try and
find which is buggered, where to get a replacement and replace
it/them.

Thanks
Tim

Some (most) pumps are prone to seizing if not regularly spun up by the system.
On some there is a large flat in an inspection cover on the end face - undo
this ( it will drip) and turn with a screwdriver the spindle underneath - it
should turn easily or you may need to free it with a twist to break the
sticking - then it should turn fairly freely.

Nick

A failure mode of these devices is that a 'dead zone' can emerge between
the cold and hot states leaving the pump completely unpowered at certain
temperatures.

That sounds exactly like the problem...so all I need to do is try and
find which is buggered, where to get a replacement and replace
it/them.

Thanks
Tim

Well after 18 months tis all fixed. You were spot on, I think there
must have been a dead zone. I looked at the wiring diagram and the
only thing controlling the pump in this way was the overrun.

Got locally from stock a Hi, Lo and overrun stat for about £22

Took the casing off and changed em all in about an hour. Fired her up
and not a bang since.

Very pleased

Tim