Boiler works fine - most of the time then goes off and stays off for 1 to 2 hours. No amount of fiddling with boiler dial or reset switch has any effect. Plumbers can't diagnose as I can't reproduce the off stage when they're here.
Its happening more frequenly (or we're noticing it more) in this cold weather
Do I get Potterton out or bin it

Cold Pompey, January 2010

Don't know if you solved this or had it answered but, just in case anybody else is experiencing this problem, I had this too, when i had the bottom case off and the tray hold the conponants hanging down, I thought the problem was the pipes to the air pressure switch got kinked when it was shut up as it seemed to work when down.
I happened to see the boiler in the dark, (before the flurecent tubes lit up in the garage) and there were sparks coming from the white plastic plug on top of the PCB. The black wire, which goes to the 2nd gas valve switch had a bad contact and was therefore giving this fault. unplugged it and reattached and now the fault has cured. HTH

Cliff Walton, December 2010

If you have a fan that starts up before the boiler ignites , then there is also an AIR PRESSURE switch.

The problem may be due to a partially blocked plastic pipe between the switch & fan.

It goes via an inline metal restrictor ( inside the plastic tube) that can block up.

Remove the tube and suck/blow so that you can hear the Air Pressure Switch clicking...then replace the tube.

A very common Netaheat fault....on the boilers with the fan + pressure switch !

Beware scrapping the boiler as most parts are still available (Ebay etc) so don`t jump to any expensive conclusions.
(and don`t believe what the CH engineers or Gas Board tell you. These old boilers are built to last....more than 28 years if necessary!)

Reg, January 2010

Thanks. I've borrowed a multimeter and will check if elec supply to boiler when its not working but should be. Best guesses from folks who should kno,w say its the pcb. If it is and the boilers 20 years old, is bin it the answer and get a new one?

Cold Pompey, January 2010

I am an unqualified muppet about boilers so my advice is worthless but... if it were mine I would need to find out if the intermittent fault was internal to the boiler or external - my potterton has a test socket E - N & Switched Live (please turn on) - I would rig up a mains neon between Switched Live and Neutral and wait for the fault to happen.

Neon OFF = fault external to the boiler - timer programmer or control head of motorised valve perhaps

Neon ON = fault somewhere inside the boiler case.

At the moment it appears nobody knows which...

But again I must stress - I know nothing...

Good luck...

Peccavi, January 2010