On Mon, 03 Nov 2003 00:40:57 +0000, geoff wrote:

In message , a_mcbride
writes

Love to solve this with a technical solution rather than a thump on
the side of the boiler.

Responding to other posts:
If the flame sensor sees no flame the boiler will lock out or at
least repeatedly try to reignite.

The Elan has a Stelrad 7B pcb inside. It is a fairly primitive
electronic ignition and has no lockout capability, it just keeps on
sparking. It is very prone to the fan control relay going high
resistance (before it melts and sets fire to the pcb). The soldering
on
the connectors on the pcb usually tends to be OK, but there could be a
problem with a look wire making intermittent connection with the
connector pin due to breaking.

The OP didn't say whether the fan was working or not. So there could
be
a problem with the APS or pcb or both

The fan continues to work when the pilot light is not alight. Have a spare
PCB due to previus problem but same fault occurs with a different PCB. Have
had a look at the APS is there any way of testing this to see if it is
functioning correctly as I don`t fancy buying a part which is not required.

Yes, having turned off the boiler, you can remove the electrical
connections and test that in the rest position the resistance between
the common and normally closed contacts is zero ohms (to the limit of
your meter).

Sucking or blowing (whichever , I don't know) VERY GENTLY on one of the
tubes to the APS, (i.e. changing over to the normally open position) you
should expect to see the same zero resistance.


If the casing is not sealing 100% as it should it can be that a
draught is set up which hinders or enables ignition to take place.
Ignition should
take place when the casing is proerply sealed.

I assume case is sealed as ignition occurs but then goes out after a period
of time, surely if the case was not sealed it would not go on for so long a
period can be up to 30 minutes.

Heat exchanger scaled ?


With ignition problems it is important to divide the problem into
smaller ones.
Where are the sparks?
No sparks = Electric or Electronic Problem/ Failure with something
else
like the air
flow or its switch/ dead short of HT leads.
Sparks in the worng place: poor insulation on the high tension
leads, electrodes worn in the wrong place.
Sparks in the right place: no gas!, dirt and crud stopping ignition.

Have cleaned all relevant parts.

The OP may just as easily find that the knock to the boiler
disturbed the air-flow switch as that there is a real problem with
the ignition.
My thoughts are moving towards the APS as I said is there a method of
testing this or do I just replace the part?



A fairly common problem is the build up of dirt around the inlet to the APS
tubes. This can cause the operation of the APS to become marginal which
becomes slightly more so as the boiler heats up (the density of the flue gases
reduce). The tubes are usually found bewteen the fan and the flue
outlet.

It is quite possible that the jolt to the boiler is able to get the
APS micro-switch to flick over.

As I said before, if the jolt causes a largish click (the gas valve) to
open then the APS system is centre stage. If the gas valve was already
open then maybe the HT leads etc.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at 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