Potterton Promax

[Rickster123]

Hi guys hope you can help me,

I have a customer that has a Potterton Promax System boiler. Its on an S plan system and feeds a megaflow and 14 rads.
The boiler fires, heats the rads/water reaches temperature then goes off as it should, temperature drops down, boiler re fires and then over heats.
Theres NO bypass fitted to the system and although i know there should be ive been told that the system has worked fine for 3 years.
He's had another engineer in who fitted a new PCB for no obvious reason, charged in excess of 300 quid and buggered off so he's a little paranoid now. I dont want to just throw parts at the boiler so any ideas would be great!
Thanks in advance,
Adam

 

[mattyp]

If the instructions state u need a bypass, the first thing i would be doing is fitting one ! I know the conventional promax doesnt req one as it has no pump over run, not sure about the system version ?

 

[Rickster123]

Im not sure to honest. Trouble is its been up and working for 3 years without a bypass. Not sure i can convince him that it now suddenly needs one.

 

[Billy Bob Bob]

i believe the system promax has a built in bypass,before going any further check the filter in the returns not blocked also take the cold resistance of the flow and return thermistors from cold your looking for 10k

 

[Rickster123]

Cheers Gas man, is the return filter easy to get to? I'll check the thermistors. The MIs point towards a circulation problem?

 

[Billy Bob Bob]

Cheers Gas man, is the return filter easy to get to? I'll check the thermistors. The MIs point towards a circulation problem?

yes it should be behind the 1/2 cap on the 22mm iso on the right

 

[Rickster123]

Great stuff thank you very much Gas Man

 

[anz]

I've had this before, changing the overheat stats cured the problem (one near fan), but another where it hasn't.

Also check wiring for pump over run?