potterton performa 28

[shanks]

Hello out there,
I've got a potterton performa 28 -4 1/2 years old.
For the last two weeks it keeps getting an ignition fault when it calls for DHW or central heating. this can be reset albeit after half a dozen attempts.
The fan starts and the air pressure switch switches. When it switches it turns the fan off - when the fan stops the APS switches the other way and turns the fan on again. This repeats several times and then the ignition fault comes on. I've checked the voltage and everything looks fine.
If i operate the microswitch independent of the APS it does the same thing.
Is there something on the PCB that latches the fan motor or am i overlooking something.
All answers gratefully received.

 

[Agile]

I would be checking the APS is actually working and the tubes and wiring are connected the right way round with continuity back to the PCB.

It might well end up being a PCB fault though!

Tony

 

[gas4you]

As Tony says, check tubes for splits etc, clean fan venturi as well.

If all these ok, then perhaps gas valve is not opening. Can you here any sparking?

 

[shanks]

hello lads thanks for the speedy replies,
I've checked the pipes and operated the APS manually.
I've checked continuity on the leads going to the board from the switch and everything is switching over as the negative pressure pulls in.
It is switching back due to loss of negative pressure (no power to the fan) because the APS turns the fan off when negative pressure is there.

The pressure switch comes off as the fan runs, the ignition starts up but is only on for about a second as the fan has already powered off.

When the cycle works the fan continues to run even when the microswitch is turned of by the negative pressure. The electrode sparks for three to four seconds and ignition takes place. I've checked the microswitch while the burner is running and there is 240V across all three contacts.
Thanks for your help

 

[gas4you]

Sounds like possibly an intermittient APS fault of failing that the pcb.

 

[baxpoti]

Check the venturi is not de-formed.