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Plumberpro, Plumber
Category: Home Improvement
Satisfied Customers: 40
Experience:  Fully qualified plumbing , heating and gas engineer 20 years experience
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Hi, Have a Potterton Prima 40f. Had various issues with it

Customer Question

Have a Potterton Prima 40f.
Had various issues with it over the last 2 years, started with the old fan cycling fault, changed the pressure switch and pcb. Ran ok for a while.
Now the fan will run constantly and only ignites intermittently. This can be assisted by removing the red pipe from the flue assembly and sucking and blowing. There seems to be an inbalance of air flow / pressure but have no way of confirming this. Having already changed the pressure switch and pcb i am suspecting the flue assembly to have corrosion.
Fan seems good and have lubricated, once the boiler heats up it will run ok for a while.
On the pressure switch in it's "home" position with the boiler switched off you should have continuity between Common and normally closed terminals but this is also intermittent and sometimes the fan won't start at all until i short out those 2 contacts.

Any help would be awsome as i've already cured a couple of faults but am somewhat stumped with this one.
Regards James
Submitted: 4 years ago.
Category: Home Improvement
Expert:  Andrew Smith replied 4 years ago.
Can you confirm the connection where the red hose connects to is clean? You may need to poke it out with a small bit of wire, it could just be a build up of dirt
Customer: replied 4 years ago.

Hi Andrew,


Yes i've poked a piece of wire through but it gets stuck after 3 inches (outwards towards the side of house), the piece of wire is rather large though, i can blow and suck without any resistance.

Regards James

Expert:  Andrew Smith replied 4 years ago.
Ok, with the cover off and everything reattached, can you hear the APS click when the fan runs?
Customer: replied 4 years ago.

OK yesterday i was wondering this and to be honest it was difficult to tell, i carried out a continuity test with my meter between common and N/O on the APS and it seemed to kick in the solenoid and ignition for a few seconds before cutting out again, it seemed that my continuity test semi closed the circuit.

I then disconnected the plug from the APS to the PCB and let it run and carried out continuity test without the DC voltage present and it seemed that the switch was still in N/C position hence not firing the solenoid.


I got the boiler lit this morning for 20 mins and has just gone out again with the fan still running.

Regards James

Expert:  Andrew Smith replied 4 years ago.
Ok, either APS, its wiring or the PCB as long as you have ruled out the fan and tubing.
Can you keep it running if you blow lightly into the APS?
Expert:  Andrew Smith replied 4 years ago.
If you take the APS out and blow into it with meter on continuity it should beep and stop as you blow?
Customer: replied 4 years ago.

yes it does, the strange thing is that when the boiler is at rest the pressure switch is still detecting minimal air flow thus preventing APS from starting the fan until i suck on the red tube?? Seems to be 2 issues here?

Customer: replied 4 years ago.

Think i may change the fan first as you need to gently blow into the red pipe to get aps to activate.

Expert:  Andrew Smith replied 4 years ago.
Strange this, usually if the fan is running then there is more than enough power to activate the APS.
Are you sure the airway in the fan is clear, can you take it out to check? You would need to take it out to swap it anyway.