Heating coming on automatically

[mcniven]

Was at a property today, system boiler with programmer & thermostat for controls.

Customer is saying that CH is coming on automatically and house is roasting. He sais that turning down of the stat, and even turning the programmer CH to off is not turning the heating off. However, the stat and programmer both work properly when making a normal demand (bringing heating on) - iv checked the rest of the system just to make sure even of HW was on that its not somehow passing by the diverter valve - this obv was not the case all working OK.

Any ideas?

 

[Killy Bing]

Three port? Sticky spindle in hw position?

 

[mcniven]

I checked the 3 port, seems OK there is an light which comes on when there is a demand.

I think its more than that, because when the boiler does this, even turning the programmer to OFF the boiler stays burning.

 

[Killy Bing]

What boiler is it?
did it go to fault while you were there?

hmm...
mind bender..

i have an idea, i will draw it out and see if it could keep the boiler running.

it is a threeport right?

 

[Simon F]

I would be checking at the wiring center (is there one?)
where is the power coming from??

 

[Killy Bing]

Hmm....if the programmer and rooms stat being turned off does nothing.

Then power must be fed into the three port to get it to switch or straight into the switch live to fire the boiler.

Thinking outside the box.
i would be inclined to tell them when it happens next to turn the boiler itself off and not at the fuse spur.
if turned back on and it doesn't fire straight back up i would say a fault on something boiler side, as demand wouldn't of changed on the external controls.

 

[thompsonbrown]

Has it got a frost stat?

 

[Ermintrude]

Sounds as if it's a system boiler and some plonker wired it wrongly. Either HW off is carried on to sl in boiler, loose wire ? Area by programmer not been retiled? Seen a few megaflows wired up with what seemed to be silly string, and then a bridge onto sl from l at boiler..... Pumps did 6 months then died

 

[Best]

I get this very often with systems that have 2 port MVs. Always one of the 2 port valves actuator has the micro switch stuck on. Even if the programmer was removed from it's backplate the heating keeps going, as it is not the programmer that supplies the power to the boiler & pump.
Can be a irregular intermittent fault, or boiler going 24hrs.

 

[efficiencyman]

Could very well be micro switch in M/V but he has said it`s a 3 port diverter valve, so it could be M/V micro sw or cylinder stat so need to verify which is calling for heat (also assuming its not a frost stat) check at wiring center if it has one. Label / tag the wires before disconnecting and testing. Are you certain it`s not the 3 port "letting by" when calling for DHW only ?

 

[dhgas]

What make of boiler is it?

 

[muffinman]

sorry this is no relevence to this thread cant sombody please tell me how to post a thread

 

[dazsl]

check the wiring first could be wired wrong

 

[newcastle phill]

Has it always done it from day one ?

Or since any servicing or repairs have been completed ?

 

[mcniven]

Thanks for answers

Potterton system boiler cant remember model its wrote down in van, nothing has changed the property is 10 months old it hasnt done it untill the last few weeks!

 

[SafeGasInstall]

Check wiring center Daren and I am sure you will find need of a new 3port valve

 

[P4ULT]

I had a very similar issue to this and it was the clock that was naff.

 

[dhgas]

Disconnect the switched live from the boiler and isolate, it will at least tell you whether it is the control circuit or boiler that is the problem.
Didn't work for me on WB 24Ri. It was the PCB that was the problem but disconnecting the SW also got rid of fault.