Protherm 80E Central Heating Won't Switch Off

[timwilbor]

I have a Protherm Combi boiler Protherm 80E which, until recently, worked perfectly. The Central Heating is on continuously now and I can'tt switch it off with either the timer switch, nor with the room thermostat. It just keeps coming on. At the moment I have to turn it off at the mains switch. The hot water works just fine. Can anyone help please. Thanks

Tim

 

[picasso]

It could be the ch thermistor has gone out of calibration, its used for frost protection and will bring on the boiler regardless of the settings.

 

[timwilbor]

Thank you....Will check that out

 

[Agile]

I would say its more likely that the boiler still thinks thee is a DHW demand.

Tony

 

[timwilbor]

Agile, If there was a hot water demand then the radiators wouldnt heat up because the DHW demand takes priority...or am I wrong ? SUrely the boiler would fire up and heat the water then shut down??? I'm a bit confused....

Tim

 

[ALCPlumbing]

The diverter valve could also be letting by. You can test this. Switch the boiler off so that the everything cools down. Switch back on and run the hot tap and leave it running. Check to see if the radiators are getting hot. As this may take a few minutes you could feel the CH flow pipe coming from the boiler. If this is hot then the diverter valve is letting by. If this is the case then it may well be that the boiler thinks there is hot water demand. If the flow pipe is cold then it most likely to be the thermistor that is to blame.

 

[timwilbor]

OK Guys, checked diverter, CH stays cold while the DHW is nice and hot. Changed the Thermistor for a new one. Still the same problem. Any other ideas??

Thanks

Tim

 

[Agile]

Agile, If there was a hot water demand then the radiators wouldnt heat up because the DHW demand takes priority...or am I wrong ? SUrely the boiler would fire up and heat the water then shut down??? I'm a bit confused....

Tim

Yes, you are wrong!

The heat goes to where the manifold section of the diverter valve sends it.

There will be a demand for hot water if the diverter valve pin is jammed out or if the microswitch is faulty. In either of these cases the temperature will be controlled by the hot water knob.

That is the most common cause of this problem.

Less common is a wrong demand for heat, often caused by timeclock faults.

Have you measured the resistance of the sensors?

See which knob controls the temperature of the uncalled for heating. That will identify which cause to investigate.

Tony Glazier