Potterton Suprema

[Lectrician]

Goes into lockout spasmodically.

Press reset, ingition sequence starts.

Boiler lights, stays lit for 3 secs or so, then gas valve shuts.

Will light 3 times, then lockout - each time it DOES light and sustain a flame for 3 secs or so(possibly more).

Sounds like the flame sensor gone squit??

It will work for a day or so every now and again, but then once it has cooled down (I believe), it will lockout again.

Any ideas?

 

[ollski]

going into lockout intermittently especially in the mornings is almost certainly the pcb...difficult to diagnose faults on these because the pcbs are notoriously rubbish and can simulate other faults.

 

[Lectrician]

What detects the presence of a flame??

It syas you should have 300Vdc at gas valve during ignition - I have 250ish - still opens.

Disconnect the plug from the gas valve and measure volts, I have 250v constantly, and 320 when the valve should be opening.

I had lockout problems before, but that was no flame at all - cleaned contacts on plug/socket on gas valve curred this - but this time, I get a flame, so valve is opening.

Pain in the arse!! Should I get an engineer out, or go for a PCB swap then??

 

[ollski]

If you get an engineer and mention suprima, and intermittent lockout you will get a pcb change anyway.....have a search on here for suprima. Would be cheaper to try the flame sensing electrode first though and the connections, they do play up aswell.

 

[Lectrician]

where is the flame sensing electrode? Is that part of the gas valve?

 

[Paul Barker]

stiff piece of wire coated with ceramic until last 4mm which may be bent over towards main burner spaced 5mm or so. Ceramic overcoat passes through casework at bottom where an HT leed conveys the information to the main PCB. The contacts the leed or the electrode could all be faulty. Clean and reassemble, make sure stiff wire end is suitably placed for a flame to pass through it. The job it does is to try and pass a dc current across the flame. The flame acts as a rectifier, if there is no flame present there is no rectification, and the pcb is looking for a dc current if it doesn't sense one the gas is shut off. In the early versions of electronic flame sensing they used a different method, but people could override it by shorting the electrode to ground, that is why they changed to flame rectification, short of putting a suitable diode in there you couldn't bipass it. Even though it is very silly to bipass safety devices when people have no heating and hot water they act very strangely. I'm not looking forward to September.

 

[Lectrician]

Had a look at the pcb today - only thing I found was a dodgy fuse holder - would have continuity, then it wouldn't, then it would!

Have managed to bodge this to stay continuous while I order a replacement to solder on.

Boiler has - touch wood - been firing fine since!

 

[Paul Barker]

nice one

 

[Lectrician]

BUMPING this back up...




--------------------------------------------------------------------------------
OK - All worked for a bit....




DIFFERENT PROBLEM THIS TIME.

Gas valve doesnt open, ignition sparks, lockout.

Metered gas valve connection - 250ish volts standby, 320 volts when ignition sparking, but valve fails to open.

I am more than certain it is the gas valve this time!

Rang potterton, they will send an engineer to fix for £235, he will replace WHATEVER needs changing (except exchanger) within this fixed price.

So, how much would a gas valve be, and who should I get to change it?? Will normal corgi plumbers be able to do this??

 

[ollski]

I had almost exactly the same problem today...3 sparks then no gas and lockout....I had no voltage across the two outermost pins on the gas valve though and a replacement pcb sorted it. If you have got the voltage then suspect the gas valve solenoid.