Worcester Bosch 28CDI issue

[Simon Foster]

We have an aging Worcester Bosch 28CDI which has developed a fault where after the heating has been on for 10 minutes or so and everything is getting hot it shuts down the flame, then instantly tries to relight but only sparks so I assume no gas is getting through. The boiler then goes into ignition lockout.

If we let it cool for 10 minutes and reset it fires up straight away, but once hot... Hot water seems to work ok if the heating hasn't been on - although I don't think we've ever run the hot water for 10 minutes anyway.

We've had our friendly heating engineer round and his first instinct is the gas valve but following the fault finder he seems to think that it indicates pcb. However I've had a look through the fault finder and in the step where you have to disconnect the multiway connector and test the resistance on a couple of points, should he have been testing on the pcb or the connector? He tested on the connector which obviously goes to the gas valve solenoids and that gave him a reading which made him conclude pcb, but I would've thought to test the pcb you'd measure the resistance on the pcb contacts?

Don't get me wrong, I do trust the guy but want to make sure I'm not chucking money on something that doesn't need replacing as both parts are quite expensive.

Cheers

Si

 

[muggles]

You've contracted him to fix your boiler. If he replaces a part and it doesn't fix it, he hasn't fulfilled his part of the contract between you, so you don't need to pay him for it. Personally I'd be looking at a different part as being the culprit as it's apparently heat-affected, but as it's a gas safety related part (if I'm correct) I'm afraid forum rules dictate that I can't tell you what it is!

 

[ollski]

It's tested on the multi connector as it checks wires and components. You rule out other things to determine a pcb fault. Makes me wonder if it is failing to rectify as flame modulates down.

 

[Simon Foster]

The engineer has ruled out everything else as the boiler is sparking he says all the pre-ignition tests are being passed, just the gas valve isn't opening.

Could heat cause one of the solenoids to stick shut? His contact at Worcester bosch seems to think the gas valve is at fault not the pcb?

 

[hertsboilers]

When sparking is happening, the gas valve is supposed to open so is supposed to get a power from the board.

So he should have measured this output from the board.

Either gas valve, or PCB board.

 

[AGAS]

Simon Foster let the man do his job , isn't this your assumption of what he has tested for ?

 

[ollski]

So he should have measured this output from the board.

It does say testing resistance though, not voltage.

 

[mcmoby69]

Friendly heating engineer?

Some friendly engineers throw white boxes on the wall day in day out.
Some throw parts at boilers till they work
Some actually know what they are doing and have a database of information they can access on site.

There are quite a few rgi's who actively pursue their interests and are constantly upgrading their knowledge.
This sounds like a basic fault and your ' friendly gas engineer' is out of his depth.