CH Boiler won't light

In message , raden writes

Fair enough

Thanks. I'll give that a go - and then watch the increase in spam :-(

Mal

snipped

Hmmm. The FSB was only replaced (along with loads of other components) two years ago. At that time, there was a pump failure which Britsh Gas fixed under a service contract. However, the boiler kept firing for a couple of seconds every 30 seconds or so, and BG sent a new engineer each time who changed a random part and left without actually fixing the problem. I eventually tracked it to a faulty tank thermostat - it was calling for heat all the time. The boiler would turn on, and then turn off almost straight away because the water in the loop was already at the boiler's maximum temp.

I don't have the service contract anymore because it cost £250 a year - cheaper to just fix problems as they arise - assuming you can find a company that can be arsed to come out :-(

Anyway, I tried the boiler this morning, and I couldn't detect any gas smell from the flue, or see any movement on the gas meter - but then I suppose for initial ignition it probably doesn't use all that much gas at all.

I'll give your advice a go and see what I can find out.

Mal

Yup - definitely no popping out. Just tick tick tick for ever.

Thanks. I'll check that out.

Mal

When I register for something like this, I always invent a special email address for the purpose(within my account range, so that I do receive emails from the organisation concerned **). That way, if any spam arrives addressed to that email address, I know the origin.

...speak of the devil....

A quirk of the 242 is that it can display wierd symptoms when some its [redundant] controls conflict.

The 242 operates as follows: DHW flow moves the diaphragm valve which close a micro switch AND a changeover water valve (4mm pipes).

These components and in the middle, front, bottom of the boiler. This starts the pump and the servo valve (lots of 4mm pipes in a 242) is in the position which uses the pump pressure to shift the main divertervalve (right, back, bottom) into DHW mode and move more microswitches to the DHW position. At this point even if the orignal microswitch is now giving a poor contact the ignition sequence will be started except for the gas valve which requires the DHW switch contact to remain good.

However none of this would explain the failure in heating mode. So check out Geoff's stuff below.

Normally if the sequence is good but there is an ignition/flame failure the button will pop out in about 10 seconds. However if the problem lies with the DHW flow microswitch it will not trip.

Unfortunately over-hauling the DHW flow switch is quite tricky and will definitely need the manual.

In heating mode the pump starts, the servo valve moves the diverter valve from neutral to CH, switches close and the ignition sequence begins.

A test you can do is to run a tap and then manually operate the DHW microswitch and see if the boiler then behaves.

Of course I had to find out the hard way by exchanging all the boards first.

(left, front, bottom) AIUI.

Ignition rate like to be around 25% of full rate so should be detectable if the gas valve were open.

There's certainly a lot of little 4mm pipes in there - but the boiler is not a combi. Theres no DHW in there at all.

Mal

I measured the solonoid resistance - it was 2kOhms. I got into the PCBs - there were three connected to another board. They didn't appear to be labelled, but hopefully a replacement should look the same as one of them!

Is there anything else I should check on the PCBs, or is it a case of swapping it out and crossing fingers?

Mal

In message , Bob writes

Sounds like the right ball park

The FSB is the top one - with the cut out switch attached

Since we seem to have run out of other ideas and you don't have much in the way of further diagnostics, yes

Well, after a two week delay due to being off on holiday, I ordered a new FSB from you and I now have a working boiler again :-) Thanks for the spot on diagnosis and the quick service!

That's yet another £100+ saving because of uk.d-i-y this year.

Mal

In message , Bob writes

No probs