Potterton Suprima

[ensign]

I have an 8 year old suprima which has stopped working. It goes through the first phase of the start up, running the pump and lighting both lights but after the 3 seconds the pump stops, the green light goes out and the red light stays on.
I went through the fault finding guide (ffg) and every relevant test resulted in a replace electronic control decision - nothing else appeared to be faulty although some tests were not strictly applicable.
I have fitted a new pcb and nothing has changed.
I cannot identify any external faults - the thermostats are switching correctly the three way valve is operating freely and as I said before, the pump is running for a few seconds.
I have checked some voltages and my questions are:
The voltage at the pump terminals in the boiler when it is running is about 20V (it varies and because it is only on for 3 secs it is difficult to be sure) - Is this right?
The voltage across SWL (switch live demand) to neutral is 20V permanently. Is this the right voltage?
The voltage at the gas valve is 3V DC not 300 as on the ffg. Is this right?
(The volt meter gives 235V AC on the incoming terminals & 16V DC on the car battery charger so I think that it is reading correctly)
Last question - does it sound like the new PCB is faulty?

 

[MANDATE]

One thing you didn't mention is the 'air pressure switch'.
The fan creates a vacuum which pulls on a diaphram which operates a micro switch.
If you run the fan ( in the right direction)from a separate supply while the boiler supply is off, you can test the continuity of the wires going to and from the micro switch.

 

[ensign]

By applying very gentle suction to the clear tube, I had been able to continuity check that the micro switch to be sure it is operating correctly. It also didn't make any difference putting suction on and holding it during the start up. I didn't want to put mains voltage onto the fan because the voltages I was picking up elsewhere had me a little concerned that 240V might not be right.
I did do a price check on the ancillary components in the boiler casing and decided that I didn't want to start changing thing like the fan because I'd broken them.

 

[AlanE]

It sounds like your voltage measuring is a bit sus - sorry!

Alan