Ariston Eurocombi boiler a/23mffi - on all the time

[SpiderDan]

Hi all, firstly this is my first post on this forum so apologies if this topic is already covered elsewhere, if so could you advise where?

Problem I have is with my Eurocombi boiler a/23mffi. It was working fine until recently, when it came on by itself in the middle of the night. It was in summer mode (i.e. hot water only) but the heating and water heating both came on. Pressing the "off" override, lowering the thermostat, etc did not turn it off again. The only solution was to turn it off at the mains.

Since then, it ignores all settings on the timers, thermostat, manual over-ride, etc - whenever the boiler is turned on at the mains, the heating and hot water run at full chat, and the only way to stop it is to turn the mains power off again.

Does anyone know what is likely to be wrong with it? My guess is the PCB because the boiler is ignoring all settings and inputs. Web searches suggest the temp prob, diverter valve and diaphragm are common faults as well. I'd like to do a DIY fix if I can

Thanks

Dan

 

[SpiderDan]

Anyone able to help?

 

[Gasguru]

Possible fault with the flow thermistor...if it's gone open circuit the boiler will jump into frost mode and fire up regardless off the settings on the front.