Heating system, Potterton gas boiler

[Murdo0202]

I have a Potterton Suprima 120L gas boiler heating a radiator circuit and the dhw. Since turning the heating back on after the summer (some 2 weeks ago) the system does not put the radiators or the hot water up to temperature. Initial firing is fine and it would appear to run for some 20mins before the boiler starts to then cut back on firing. Not sure if just a coincidence but when the programmer is moved from the 'timed' operation to 'on' the heating and hw do eventually reach normal temp.
Radiators have been bled and there does not appear to be sludge either at the pump or at the rads.
Any ideas

 

[45yearsagasman]

What pump have you got fitted to your system, and how have you checked it? It does sound like a circulation fault on first reading.

 

[Murdo0202]

Hi Pete,
pump is standard Grunfos 15/30 pump.
Photo attached of setup, pump shown on rhs

 

[45yearsagasman]

If thats a picture taken today, then I would suggest the boiler needs expert attention as the combustion chamber has been opened. Please get it checked for safe operation and turn it off until it can be verified.

 

[Murdo0202]

Hi,
yes picture taken today, just opened the housing to check cables ect.
I am a building services engineer but more used to design rather than fault finding on this type of system. Will replace housing shortly.

 

[Murdo0202]

Hi, just to answer the question about the pump working, pipework before and after hot so assuming pumo is ok. I can check live neutral and earth with multimeter if you think its an issue?

 

[45yearsagasman]

I'm sorry, please don't take offence, but you are probably out of your comfort zone with this. For your own safety, I recommend you get the boiler checked for safety asap. I believe it to be a circulation fault, but there are many things to check and this is best left to experts. I wish you luck.