Honeywell ST7100

[rlw]

I have had a new boiler installed but kept the old controller as it worked fine. Now the heating keeps coming on at different times it is set to (3am in the morning is the worst when it is so hot!). Both the plumber and electrician can't understand it which hasn't helped me much!

When it randomly comes on there is no way of turning it off unless I turn the thermostat right down (even though every rad has a TVR).

Anyone any ideas, or do I need to replace the timer box - it is the Honeywell ST7100 which I am guessing is old?

Thanks.

 

[electronicsuk]

Perhaps the system has been connected up in such a way as the programmer is bypassed completely and the only control over the system is via the thermostat, hence the apparent 'randomness'. I can't imagine why any of this wiring should have been altered as part of installing a new boiler, unless you have gone from gravity HW with tank to a combi and have had to have some wiring removed?

 

[rlw]

Thanks for your reply.

I can't magine why this would happen. We have kept to the gravity system, and there is new wiring to the boiler and themostat. The hot water works fine and comes on and off as it should.

The heating seems to come on at the times prgrammed, but then comes on when it shouldn't......expensive!

The electrician seems to think it is the timer, however I am not so sure??

 

[rlw]

PS - when the heating is not on and I do turn the themostat up it comes on?

 

[electronicsuk]

PS - when the heating is not on and I do turn the themostat up it comes on?

In that case, your electrician has almost certainly made a mistake when rewiring the stat and boiler. If he hasn't been able to identify a simple fault and is insistent on blaming the programmer (and charging for replacement) then it probably isn't worth having him back. However, give him a fair chance, if you point out that the system will run from the stat when the programmer is off then it should be a big help to him.

BUT... before you do any of that, are you 100% sure that what you have is a standard room stat, and is not designed for use as a frost stat? If it were the latter, the heating would always come on regardless if the temperature drops below that set on the stat.

 

[rlw]

Ermm I think it is a room stat. All the rads have new Trvs and then the grey room stat (already there but had new wiring to it) was kept in the living room - without the TVRs on the rads. (Sorry I am a lady on her own and not very technical!)

Is it worth getting him back in? He has already blamed the programmer ....

strange how it comes on at random times....

 

[electronicsuk]

Is it worth getting him back in? He has already blamed the programmer ....

strange how it comes on at random times....

If you're 100% sure that the stat didn't used to control the heating when the programmer was off, there has certainly been a mistake made somewhere. If your electrician wasn't aware of this issue then it would be unreasonable to expect him to find the fault, in which case you should get him back and pass on this information.

If, on the other hand, he's aware that the thermostat hasn't been working properly since he rewired it and he still blames the programmer, you might be better of finding someone else. If the programmer is old then it would seem sensible to replace, but it seems unlikely to be the cause of the problem in your case.

 

[rlw]

Many thanks for your help.

I think I will do some tests to def see if it running from the themostat (I am positive the heating wasn't run off this before) and then get him back in if it is.

If not....then a new programmer might be the solution.

 

[gas4you]

Firstly when fitting a new boiler the system should have been converted to fully pumped to conform with the energy efficiency regs, so I am instantly suspicious of the entire job. I wonder if it was registered with CORGI

Have you a motorised valve on the system? Could be sticking open.

If not has the pipework now been changed so that when the boiler fires up for HW the rads get hot through gravity circulation?

 

[rlw]

Hi - yes it was def fitted by a CORGI guy (got a certificate etc). He was very good and fitted new pipework ect as it was moved. He has checked it all over and is pretty sure its the electrics. It's the electrician who I am not sure about!

Where will I find the motorised valve?

I haven't noticed if the CH comes on at the same time as the water, although this wouldn't explain why it comes on at 3am, 3pm etc ....?

 

[electronicsuk]

Have you a motorised valve on the system? Could be sticking open.

Hadn't thought of that, but it doesn't explain the randomness, as the valve shouldn't come on by itself.