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NiceCupOfTea

Original Poster:

22,824 posts

134 months

[news] 
Wednesday 28th December 2011 quote quote all
Could use some help please!

We have a Potterton Suprima 80 boiler with separate heating and hot water circuits. Timer controls HW as normal, with the heating side of the timer set to "ON" - timing of heating is controlled by a remote digital thermostat/timer. (Honeywell CM927) Hope that makes sense.

The timer/stat were installed a couple of years ago and have worked very well.

All was fine until a couple of weeks ago. We have a British Gas "servicing" contract (ie, bloke comes out, hoovers it, and checks CO levels every year!) - he did his stuff and left.

It was fine.

Went away over Christmas and put it into its holiday mode, where it maintains a minimum temperature that you specify (16 C in this case).

Came back to find the house baking - 34 C according to the thermostat, with the "target temp" still 16 degrees but the boiler full on. Had to override the thermostat base station (bit actually attached to the wall) by toggling it on and off.

Just today noticed it was very hot again. Target temp 20C, actual room temp 23C. Stat saying boiler was off, Stat base station light off indicating no call for heat. Boiler on full whack. Toggled base station call for heat button on and off, and boiler switched off.

I had initially suspected the thermostat batteries, but the low battery indicator was not on. Now I don't think that is the problem at all, as the base station was suggesting there was no call for heat, but the boiler was on.

Is there some way the gas engineer could have buggered up the boiler so that it is not always detecting a CFH signal correctly? I thought it was a constant voltage / no voltage for heat / no heat, rather than a "toggle" signal that it might miss...

Does this make sense to anybody?

NiceCupOfTea

Original Poster:

22,824 posts

134 months

[news] 
Wednesday 28th December 2011 quote quote all
A bit of googling has suggested people have had similar issues when their zone valve has a dodgy microswitch. Could this explain why the stat isn't calling for heat but the boiler is on? We have separate valves for HW and CH.

We have BG Homecare 200 ( http://www.britishgas-savings.co.uk/british-gas-se... ) which doesn't specifically mention valves but does say "Repairs to central heating boiler, controls, radiators, pipework and hot water system" which I would hope covers it (nothing on the higher levels says anything about valves)

Rickyy

4,557 posts

102 months

[news] 
Wednesday 28th December 2011 quote quote all
My first thought was a sticky microswitch, but this wouldn't allow the radiators to get hot as the valve would be closed.

Although it could be possible that the whole valve is getting stuck in the open position. What make/model is the CH zone valve?

oldcynic

1,674 posts

44 months

[news] 
Wednesday 28th December 2011 quote quote all
NiceCupOfTea said:
We have a British Gas "servicing" contract (ie, bloke comes out, hoovers it, and checks CO levels every year!)
Can't you just call British Gas and make use of the contract you pay for?

Deva Link

26,934 posts

128 months

[news] 
Wednesday 28th December 2011 quote quote all
NiceCupOfTea said:
Toggled base station call for heat button on and off, and boiler switched off.
That would tend to imply a problem with the base unit.

I suppose the heating zone valve could be sticking open - so keeping the microswitch switched, and it's that switch which the boiler is powered through. Toggling the base unit could be enough to free the valve. Bit of a long shot though.
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NiceCupOfTea

Original Poster:

22,824 posts

134 months

[news] 
Wednesday 28th December 2011 quote quote all
Rickyy said:
My first thought was a sticky microswitch, but this wouldn't allow the radiators to get hot as the valve would be closed.

Although it could be possible that the whole valve is getting stuck in the open position. What make/model is the CH zone valve?
They're both silver Honeywell valves - no obvious model numbers, one says V4043H1106 and the other V4043H1056 but they may be serial numbers. They both have metal switches on the back with 2 positions - manual & auto. One of the switches seems to be in the middle, while the other is set to auto. No idea what that means.

Re: using the contract - yes, I fully intend to, but I would like to have an idea of what is wrong first.

Deva Link

26,934 posts

128 months

[news] 
Wednesday 28th December 2011 quote quote all
NiceCupOfTea said:
One of the switches seems to be in the middle, while the other is set to auto.
Is the one in the middle in a circuit (hot water or heating) which is on at the moment? When off the levers should rest at auto - you can manually open them and clip the lever against the catch for draining down purposes.

Rickyy

4,557 posts

102 months

[news] 
Wednesday 28th December 2011 quote quote all
Next time you come home and find the heating is on, try moving the lever on the CH zone valve, try and move the lever side to side. If it moves freely, the valve is in the open position.

If it is in the open position, access the wiring centre for the heating and check for power on the brown wire of the CH zone valve. If you have 240v on it, there is a fault with the stat. If there is no power on it and the valve is definitely open, the fault lies with the valve.

They are usually motor open and sprung closed. The valve could be stiff and not returning correctly.

Most honeywell valves have removable actuators, you can remove them by taking off the silver cover and undoing two screws that go through the actuator in to the brass body, once removed try freeing up the valve slightly by opening and closing it manually with a set of pliers.

If the valve has four screws and/or an orange gasket between the actuator and valve body, DO NOT remove the actuator, you WILL get wet!

oldcynic

1,674 posts

44 months

[news] 
Wednesday 28th December 2011 quote quote all
Deva Link said:
NiceCupOfTea said:
Toggled base station call for heat button on and off, and boiler switched off.
That would tend to imply a problem with the base unit.

I suppose the heating zone valve could be sticking open - so keeping the microswitch switched, and it's that switch which the boiler is powered through. Toggling the base unit could be enough to free the valve. Bit of a long shot though.
A problem with the base unit would be easy to spot with a multi-meter - beware there'll be mains voltage under the cover.

If the problem started during a routine service then it's as likely a loose wire disturbed by the service guy - check all the screws are properly tightened up and the wires are firmly in place etc etc. Quite why toggling off & on would clear that fault I've no idea.

NiceCupOfTea

Original Poster:

22,824 posts

134 months

[news] 
Wednesday 28th December 2011 quote quote all
Any easy way of working out which valve is CH and which is HW?

oldcynic

1,674 posts

44 months

[news] 
Wednesday 28th December 2011 quote quote all
NiceCupOfTea said:
Any easy way of working out which valve is CH and which is HW?
Select CH or HW and feel which pipe gets hot?

Rickyy

4,557 posts

102 months

[news] 
Wednesday 28th December 2011 quote quote all
Without seeing your set up no. But assuming your zone valves and cylinder are in the same cupboard. The DHW valve will have pipework leading into tappings on the side of cylinder and the CH would usually have pipework disappearing into the floor.

Failing that, switch the Hot Water on and feel which lever becomes loose.

eastlmark

1,186 posts

90 months

[news] 
Thursday 29th December 2011 quote quote all
I had the same issue earlier in the year. (not caused by BG though but read on!) I was mystified why the heating would not turn off and even pulled the timer from its base plate to toatally disconnect it, yet the heating still carried on. What I later learned (from a helpful PH user) is that the timer does not switch on the boiler as such, but directy feeds the valve which in turn then operates the valve microswitch to bring on the boiler and pump. My problem was a broken spring in the valve preventing it from closing and therefore not altering the microswitch contacts.
A new valve was therefore fitted by BG as part of my plan which cured the problem........
as I said though, read on.....while doing so the idiot BG engineer managed to bust my water tank flooding and bring down half the ceiling in my kitchen below!

NiceCupOfTea

Original Poster:

22,824 posts

134 months

[news] 
Thursday 29th December 2011 quote quote all
Update:

Heating did the same thing again this evening. Went up and checked the zone valves - one appears to go into the bottom of the hot water tank, the other goes down through the floor - I assume the latter is the CH zone valve. Both of the little metal switches were in the same place, both seemed to move with a little pressure. Manually toggled the thermostat on/off but the boiler didn't shut down. Switched off the CH altogether at the timer, but the boiler didn't shut down yikes Hot water was also off.

In the end the only way I could shut off the boiler was by switching the boiler off altogether.

I'm not terribly confident about waving multimeters around live distribution panels so will leave that for now.

Am I right in thinking that if switching off the CH & HW at the timer doesn't stop the boiler, it can't be anything to do with the 'stat (as the stat is effectively a switch inline with the timer)??

oldcynic

1,674 posts

44 months

[news] 
Thursday 29th December 2011 quote quote all
Maybe the boiler control is fked? Hard to tell unless you confirm the signals being sent to it.

Probably time to get the professionals in.

eastlmark

1,186 posts

90 months

[news] 
Friday 30th December 2011 quote quote all
NiceCupOfTea said:
Update:

Am I right in thinking that if switching off the CH & HW at the timer doesn't stop the boiler, it can't be anything to do with the 'stat (as the stat is effectively a switch inline with the timer)??
does sound exactly like the same problem I had in my post as above. A room stat will operate the valve only once it has a feed from the timer, so its not likely to be the problem.

Deva Link

26,934 posts

128 months

[news] 
Friday 30th December 2011 quote quote all
NiceCupOfTea said:
I'm not terribly confident about waving multimeters around live distribution panels so will leave that for now.
There's not much point in finding what's wrong anyway - as you've got coverage, just get BG out to find & fix the fault.

NiceCupOfTea

Original Poster:

22,824 posts

134 months

[news] 
Friday 30th December 2011 quote quote all
Yes indeed, just like to try and understand it!

BG coming out on Tuesday. Changed the batteries in the stat anyway, not had an issue yet but will keep an eye on it.

Thanks all!

spike ST500

721 posts

38 months

[news] 
Saturday 31st December 2011 quote quote all
lets just hope it does the problem while the guy is there!

I'd be looking at the CH valve sticking on myself.

NiceCupOfTea

Original Poster:

22,824 posts

134 months

[news] 
Saturday 31st December 2011 quote quote all
spike ST500 said:
lets just hope it does the problem while the guy is there!

I'd be looking at the CH valve sticking on myself.
Indeed. It seems to behave itself in the morning, just late afternoon & evening it just stays on. I had the boiler off for most of the evening and tried to switch it on before I went to bed so we would have hot water this morning, but it just fired up despite the stat being low and the hot water timer off...

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