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
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