Potterton Profile 50e ignition problems

[Steve]

Hi,

My Potterton Profile 50e has been starting only intermittently recently. I've been trying to figure out what the problem is using the handy fault finding chart at the back of the boiler manual, but I'm not too sure exactly what the problem is.

When I call for heat, I hear the fan switch on (not cycling on/off, it's on continuously). Up until a couple of weeks ago I'd get one or more sparks from the electrode - sometimes the pilot would light first try, sometimes it wouldn't light at all. If it doesn't light after 3 or 4 attempts, the fan will keep going but ignition will stop. Usually, by switching off then switching on, it'll light on the second or third attempt.

However, it's been deteriorating recently - I'm now rarely getting any ignition sparks. Also, on one of the ignition attempts this morning, I noticed that the pilot light started up but then died out a couple of seconds later.

One slightly disturbing thing I noticed when listening carefully this afternoon was that after the fan starts up and before the ignition attempts, there is a electric buzzing/crackling sound, as if electricity is arcing somewhere.

From the fault finding chart, that puts my problem at either a leaking case door, a problem with the electrode lead, a problem with the electronic control, a problem with a blocked pilot jet, or a problem with the solenoid.

Does anyone have any suggestions where/how I should start isolating the fault, or for what the problem could be?

[Steve]

A correction: the buzzing/crackling sound occurs immediately before the

*fan* starts, not before the ignition attempts.

Steve

[Ed Sirett]

Having read the other post in this thread:

The PCB (on this boiler) is mixture of mains , HT and maybe some low voltage stuff as well.

You could have a failing APS which might be causing these symptoms. Your PCB may have problems. Your ignition lead might be shorting out - but that would not account for the buzzing noises and the failure of the pilot light.

If you hadn't mentioned the buzzing _before_ the fan starts then I'd have said go for the APS first. Now I'd go for the PCB first.

[Steve]

How would I go about determining whether it's the PCB or the APS? A few seconds after the fan starts, I hear a single click, which could possibly be the PCB relay - I'm not sure what else would make a click a couple of seconds after the fan.

Unfortunately, the problem is getting worse and I'm not getting any sparks at all anymore, so I can't see if I get additional noises when the boiler does successfully light (which would presumably be the ignition relay).

Thanks to you and Geoff for your replys!

Steve

[Steve]

Out of interest, why do you say that?

I've just tried checking the impedance of the APS when blowing and not blowing. It seems to be working correctly, but I hear a crackling sound (the membrane inside the sensor, I assume) and was wondering if this would have been what you thought the buzzing sound was - if it happened after the fan starts (which would cause a pressure change, hence crackling from the APS).