Potterton Performa 30 HE no central heating

[g4224wil]

Hi

customers boiler is not working for the central heating.

Hot water is working fine, ignition sequence for heating is fine and it will fire when cold for a few seconds before temp reaches 80 and it cuts out
there are no faults showing up.
fan is working, pump is working, heat exchanger removed and cleaned, bypass pipe removed and cleaned, isolation valves all cleaned out.

not been able to open the filter on the return valve - can't undo nut - any suggestions? it'll be just my luck there is a blockage in there.

also any suggestions for what else to test?
thanks

 

[king of pipes]

Are you sure the valves on the flow and return are open ? Because all the symptoms point to something being shut

 

[Stu-B]

As kop says, symptoms suggest no flow so I’d check the rads too, I went to a job few weeks ago where all the rads were closed on the TRV’s and the boiler was doing the same thing, ramping up to 80 and shutting off within a minute.

 

[garygvl]

Is divertor valve stuck in hw position

 

[Christopher buzzard]

Had it before where the black handles underneath appeared in the open position but actually when taking them off the plastic was screwed. Just round off and not actually turning the brass isolation valve.

 

[EvilDrPorkChop]

Filter in return valve. Had the same on many Glow Worm betacoms, filters block up and won't circulate round heating circuit.