Gas boiler ignition problems

My ideal elan 2 50FF was failing to ignite automatically having checked it over for loose connections I switched the electrics back on and it still failed to light. Whereupon I decided to put the bottom plate which is just really to prevent anything from getting into the electrics it wouldn`t quite fit so I had to be rough with it and accidentally knocked the side of the boiler, whereupon the boiler started clicking and fired up. Now the boiler lights but after a short time anything from 10 to 30 minutes it fails to ignite but the fan still runs if I give it a thump on the side casing then the injector fires up.
I have also noticed that the downstairs radiators are not getting as warm as the upstairs which seems to me to suggest that my pump (13 years old) is failing. Could this also be related to the problem with the ignition? Maybe the flow rate is not sufficient and the boiler is refusing to light for safety reasons. Or is it some other problem perhaps with the Honeywell gas control?
Love to solve this with a technical solution rather than a thump on the side of the boiler.
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it needs to rather than having a permanent pilot light?
If so, it sounds similar to my Baxi Solo 70/4 PF.
My boiler is *very* sensitive to the tightness of the screws holding the outer casing on - tighten them too much, and it fails to fire - even though the fan is running and it is sparking like mad. I have come to the conclusion that tightening the screw in some way alters the spark gap and stops it from working in the correct way (some complicated ionisation process which I don't fully understand!).
Maybe you have a similar problem. Do you have an installation manual which shows you how to check and adjust the gap? If so, have a go at that.
HTH, Roger
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I have just had a problem with my combi failing to ignite. It turns out that the pump has failed, and these things have so many interlocks on them that they won't try and ignite if there's a problem in some other part of the boiler, e.g. a failed pump, so you could be right. The fitter chap who looked at mine took the plastic cover off the electrics at the side of the pump and measured a voltage there with his meter ( mains 50Hz I think ), so if your pump has a voltage at its terminals but isn't operating then that could be your problem. So could a host of other things mind. He also took a large slotted screwhead off the front of the pump and waggled a screwdriver in the rotor shaft end behind to see if he could turn it, but declared it stuck - another thing you could try if you're technically minded. The ionisation sensor apparently is at the opposite end of the flame burner to the spark gap electrodes - it checks to see that the flame front has spread right from one end of the burner to the other. I imagine if it has gone duff then the unit won't light as it thinks the burner hasn't lit completely.
Andy.

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On Sat, 01 Nov 2003 17:21:50 +0000, a_mcbride wrote:

Responding to other posts: If the flame sensor sees no flame the boiler will lock out or at least repeatedly try to reignite. 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.
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.
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.
The key test is when the knock happened was there initally a big click from the gas valve (problem is not with the ignition) or did only the ignition sparker start to be heard.
HTH
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
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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

--
geoff

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geoff wrote:

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.

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.

Have cleaned all relevant parts.

testing this or do I just replace the part?
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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.

Heat exchanger scaled ?

--
geoff

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

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
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Thanks Ed for advice have bitten the bullet and replaced the APS and that seems to have solved the problem many thanks again for the help and advice.
Andrew
Ed Sirett wrote:

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Try a new air pressure switch. Its the round disc under the bottom left of the boiler. take the bottom plate off to see it

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