Potterton promax combi - Sticking on DHW mode

[Eddamoo]

Hi all, the mother in law has a Potterton promax combi he plus which is stuck in DHW mode causing the central heating not to come on.

When visiting today, I noticed the 'tap' led was permanently lit despite no DHW demand and the heating thermostat requesting heating. The boiler does try to heat the water but as there's no DHW flow it rushes up to 90C and then shuts off.

I could however get the boiler to switch over to central heating by running a hot tap very slowly. Maybe that released some pressure from the DHW system and finally caused the heating to fire.

So it seems like it could be a diverter valve possibly or some pressure switch issue... Does anyone have any ideas please?

Many thanks!! Ed

 

[CBW]

Float switch stuck in the open position. If she needs heat, you could remove the Hall effect sensor and leave her without hot water from the boiler.

 

[cross thread]

Sometimes if you rapidly open and close the hot tap it may free it off

 

[Eddamoo]

Thanks for your replies guys! Yeah that seems to be it! I tried cycling it after tapping it with a metal rod and it is now cycling freely!

Will order a new one but that should keep her warm in the meantime! Thanks again!!