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?

On Sat, 17 Sep 2005 19:34:40 +0100, Steve wrote:


> 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.


A correction: the buzzing/crackling sound occurs immediately before the
*fan* starts, not before the ignition attempts.

Steve

In message , Steve 
 writes

>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?


I'd suspect a cracked joint on the pcb if you can hear arcing and the 
problem's getting worse

-- 
geoff

On Sat, 17 Sep 2005 21:56:49 +0000, raden wrote:

> I'd suspect a cracked joint on the pcb if you can hear arcing and the 
> problem's getting worse


The PCB should be fairly low voltage though, shouldn't it? Not enough to
cause arcing?

Steve

In message , Steve 
 writes

>On Sat, 17 Sep 2005 19:34:40 +0100, Steve wrote:
>
>> 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.
>
>A correction: the buzzing/crackling sound occurs immediately before the
>*fan* starts, not before the ignition attempts.
>

Then apart from what I said before, could be the air pressure switch or 
a relay on the pcb

-- 
geoff

In message , Steve 
 writes

>On Sat, 17 Sep 2005 21:56:49 +0000, raden wrote:
>> I'd suspect a cracked joint on the pcb if you can hear arcing and the
>> problem's getting worse
>
>The PCB should be fairly low voltage though, shouldn't it? Not enough to
>cause arcing?
>

You don't know much about CH controls do you ?

-- 
geoff

On Sat, 17 Sep 2005 19:34:40 +0100, Steve wrote:


> 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?


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. 


-- 
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk 
Gas fitting FAQ  http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

In message , Steve 
 writes

>On Sun, 18 Sep 2005 12:40:59 +0100, Ed Sirett wrote:
>
>> 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.
>
>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).
>

You need a meter

You need to switch off the boiler

Remove one of the tubes going to the APS at the other end so you can 
suck or blow to activate the APS

The APS is a changeover microswitch connected to a membrane

Now, remove the connector labelled Air pressure switch from the pcb
(I can't remember off hand which of T4, T5 and T6 are the normally 
closed, common and normally open leads, you will have to either look on 
the APS or try and see). If you measure at this connector, you are also 
checking the wiring to the APS

At rest, two of the contacts should be a short circuit. By this I mean 
less than a couple of ohms. Check the resistance of your probes first.

Now, suck or blow (depending on which tube) GENTLY (so you don't rupture 
the membrane) to change the APS in the normally open position. Again, 
you should see a resistance of less than a couple of ohms.

Do this a couple of times for consistency

Finally, activate the APS and bend the pipe - make sure that the APS 
doesn't return to the rest position to check that the membrane is intact


-- 
geoff

On Sun, 18 Sep 2005 12:40:59 +0100, Ed Sirett wrote:


> 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.


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).