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