Potterton Prima 50F Help appreciated

[Hp1]

Hi,

I was called to a Prima 50F. The boiler sometimes fails to light (automatic ignition), however it energises the main gas solenoid thus expelling unburnt gas through the flue. I have looked at the installation manual on the Parts Arena site but this is very vauge.
The pump comes on the Fan goes, makes the air switch which in turn allows the spark to ignite the pilot. In most cases the boiler ignites the pilot and thus allows gas to flow to the main burner and the boiler operates.

My question is what type of Flame supervision device is fitted to this boiler. Is it flame Rectification? If it is flame rectification why does it allow the main gas valve solenoid to energise? (I see voltage at the solenoid). If it is not the Flame failure device it can only be the pcb. How to I check this. These boiler did not work on Flame conductance, did they?



Help much appreciated.

 

[ollski]

You need to check that there is no continuity from the white wire from the pcb to the gas valve and earth, this will cause exactly the problem you have. I have always replaced the wiring with this faultand 9 times out of 10 it has fixed it.

 

[Hp1]

Hi Ollski,

Thank you for your reply, However can you please clear up a few points.

When you say check that there is continuity from the White wire from the pcb to the gas valve and earth. Do you mean check between White wire to gas valve and body of the gas valve?

When you say you replace the wiring. Do you change the wiring harness between gas valve and pcb?

Also is the white wire the signal wire? would this not blow the fuse if continuous to earth?

Is the flame supervision based on flame rectification? Should it not fail safe?

Do you have any other wiring diagragms. other than the once in the manual (they leave a lot to be desired).

Once again thank you for your help