Heating turning on when taking shower, with thermostat off

[ioannisg]

Good morning everyone

I am facing a peculiar problem in the new house I've moved in and would like to understand whether this is normal behaviour or not...

I have a Potterton 185 Powermax boiler with the integrated programmer. Also a room thermostat wired up to the boiler.

Now the problem. When having CH ON on the programmer and Thermostat off (even physically disconnected) and running the hot water, heating fires up to warm up the internal tank. However my radiators are also hot!

If I have CH to OFF then the radiators are cold when running hot water.

Thermostat is getting power when CH is ON and when CH is off it is not. Also it does indeed control the heating, only when the heating is not on for hot water!

So is this normal or there's something wrong? What should I look at as its driving me crazy

 

[45yearsagasman]

These boilers have a diverter valve which is prone to siezing. The internals can be replaced, but is really not a diy job, as access is required to the area of the burner etc.

 

[ioannisg]

These boilers have a diverter valve which is prone to siezing. The internals can be replaced, but is really not a diy job, as access is required to the area of the burner etc.

Thank you for the quick replying! I was thinking the same but what threw me off was the fact that with CH off at the programmer the hot water store warms up and runs hot without the radiators coming on. Thoughts?

 

[45yearsagasman]

As all the wiring is pre installed, I think we can rule out a fault there. If as you say you physically disc the room stat, have you checked the room stat connections at the boiler? My suspicions are still with the diverter valve.

 

[ioannisg]

Untitled

• ioannisg
• 28 Oct 2014
• 1

I've been trying to get my head around the wiring of the boiler whilecwaiting for the engineer to try and fix the issue. I've attached the wiring diagram but can't seem to find the diverter valve on it, any clues?

 

[ioannisg]

So boiler engineer came over and the problem was far more "interesting"! The previous owner had installed a relay between the thermostat connectors on the boiler and the gas ignition point on the boiler! So whenever the ignition was on the thermostat controls were overriden and the heating was on! Needless to say that this contraption was removed.

The engineer was at a loss on why this was installed.

Any ideas??

 

[MaxPower185]

It was probably an attempt to disguise the horrific kettling noise from a poorly maintained system.

Keeping the heating on whenever the boiler is firing makes sure that the water in the thermal store is strirred. This reduces the chance of hotspots and so reduces the chance of kettling in the boiler.

When these things get sludged and scaled up, they kettle like crazy and because of their size, it sounds like a small child is trapped inside trying to escape with their feet and fists.

 

[ioannisg]

Thank you maxpower

I've had this fixed for a month or so and all seems to be working fine, haven't heard any weird noises but fingers crossed that won't hapoen, at least this year as cannot afford to replace the boiler just yet