Combi boiler electrical fault

Hi all,

I've a Worcester oil fired condensing combi boiler that I've complained about here on previous occasions. This time it's gone t*ts up as a result of a suspected electrical fault. I suspect it's electrical since the 230v terminal which supplies an external room stat has gone right down to just a few volts. But I've lost hot water as well as heating so it must be a fault that's common to both sub-systems. The boiler 'power' light is illuminated; the 'lock out' light is not, and the on1/on2/off/time lcd panel is likewise showing the usual correct indications. When I turn the hot tap on, just one of the relays on the pcb activates and there's a faint hum from the boiler's internals, but nothing from the fan/burner etc. One clue is that the boiler has recently been taking progressively longer in firing up after switch-on until its now got to where it doesn't fire up at all. Any troubleshooting suggestions, guys?

cheers,

cd

Reply to
Cursitor Doom
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Cursitor Doom wrote in news:ld158d$4rq$ snipped-for-privacy@dont-email.me:

A faint hum from the guts of the thing, I would say.

  1. Knackered oil pump.

  1. Jammed fan.

  2. Capacitor kaput.

In that order.

Replace capacitor.Cheap.

Take off oil pump and start boiler. If it revs up then it's the pump.

If it still hums then motor stuck.

Reply to
Heliotrope Smith

It's not clear to me which capacitor you're referring to here. You may be right about the other parts, but I'd be surprised, since the boiler was installed brand new only just over 2 years ago (warranty timer's kicked in, predictably) although I have discovered it's not been serviced since then, if that's relevant.

Reply to
Cursitor Doom

Also even good looking relays can deceive one into thinking its actually connected. Could be poor regulation of supply to relay or just knackered or tarnish on the contacts. I hate boilers.. Brian

Reply to
Brian_Gaff

IMO (knowing very little of boilers but quite a tidy bit about electronics) shorting out the relay secondaries to get some reaction is the first line of investigation here after checking the more obvious things like circuit board fuses and whatnot. It's just a bloody nuisance the things appear to be hard wired onto the main pcb rather than the plug- in type which would have made life so much easier.

I guess there must be a voltage regulator here somewhere that should also be checked, but I've yet to find one...

Reply to
Cursitor Doom

I've wondered if there is potential for a replacement pcb with simple discrete logic and plug in relays. US gas fired hot air heaters seem to have used this system for ever and are very easily repaired. Are the modern pcbs multi layer? For reliability and cost, IBM IME always used single sided boards with links where necessary when handling power.

Reply to
Capitol

All the scope in the world, I'd say. But it does demand a good deal of time to perfect such a replacement control system. The main drawback with your idea is the extra cost of a decent power supply. As things stand it seems like everything just runs off 230v!

Single sided board with surprisingly few components; just four (Chinese) relays and a bunch of strip connectors to interface to the off-board components (again, not much at all in the way of electronics). I'll bet they want a mint from a new main pcb, though!

Reply to
Cursitor Doom

The symptoms you describe seem to point stalled motor.

Does the boiler make the same noises when calling for heating only?

I am refering to the motor capacitor. The motor drives the combustion air fan and the oil pump.

A knackerd oil pump is the usual culprit. Not likely to be worn motor bearings on so young a boiler.

A duff capacitor will of course prevent the motor starting and cause it to hum.

Reply to
Heliotrope Smith

I'm sure you'd be bang on if this boiler were a few years older, but I'm still unconvinced. Thing is, none of the above you mention accounts for why the power to the external thermostat has gone. That strikes me as some sort of signal control issue. I'm going to start shorting out relays and sensors this evening, but I'll certainly follow your suggestions if I make no progress on the more readily accessible steps I plan to make first....

Reply to
Cursitor Doom

Sorted. It was the timer module. Sat there saying everything was fine, but wasn't actually sending enable signals to the relevant relays when it was supposed to be ON. The precise problem appears to be the buttons, which are only making intermittent contact, I discovered, so I can't simply snip out a faulty component like a resistor or a cap and replace it. Got to get a complete new module. Typical!! :(

Reply to
Cursitor Doom

Cursitor Doom wrote in news:ld3u36$vst$ snipped-for-privacy@dont-email.me:

Well done! Goes to prove it is easier when in front of the boiler.

Reply to
Heliotrope Smith

Thanks. As a coda I should just make a small correction for the benefit of others attempting troubleshooting of the same boiler. It wasn't one of the switches on the front panel (I called it a 'timer' but I think 'programmer' is more correct) but rather a sub-miniature relay on the programmer board that turned out to be the true culprit. Giving it the slightest tap with a fingernail 'cured' the problem.

You think you're supporting British industry and getting better quality by buying a British boiler, then it turns out half the internals are still cheap s**te sourced from China, and a chain is only as strong as its weakest link. Would it really have cost that much more to use decent quality relays in this design - and thereby improve reliability markedly? These miserable penny pinchers obviously think so. Therefore, Worcester- Bosch boilers of Worcester UK., consider yourselves named and shamed!

Reply to
Cursitor Doom

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