Potterton Promax 33 HE Plus combi - heating on when not selected.

[1917PT]

I have a Potterton Promax 33 HE Plus combi boiler. All appeared to be working fine until a couple of days ago. Hot water only is selected on the boiler front, the boiler heating water temp is turned right down and the roomstat is turned right down. However, when I run hot water the radiators get hot. When I stop running hot water the pump overruns for short while then shuts off. The boiler is not indicating any fault condition, the pressure is fine, everything appears normal. Any thoughts?

 

[Dan Robinson]

Will need to check a diagram of the boiler, but sounds atypical of a diverter failure.

 

[1917PT]

Thank you Dan.
I've been poking around myself this afternoon and have probably come to the same conclusion. I can feel the diverter valve motor running when I switch between hot water only and hot water + heating and the motor plunger moves up and down, so it's probably the bit the plunger pushes on in the diverter valve body that is not free.

 

[gigz]

Sounds like you need a new cartridge. Not sure if the promax has a bypass, if it does you'll need the full valve (don't think it does though).

 

[1917PT]

I have seen replacement cartridges for sale for both types of Diverter valves (with and without by-pass). How do I tell whether I have a by pass fitted or not?

 

[Dan Robinson]

Look for a little copper tube joining the left and right brass manifolds.