Boiler ignition problems

[Lobster]

I have a Sime Friendly Format 80E combi boiler in a house I rent out. For about a year it's been having an occasional problem of cutting out, and requiring to be manually reignited. An engineer has tried to fix it but couldn't find the problem, so it was agreed to leave it alone. However, the problem has got steadily more frequent, to the extent that it was no longer reasonable to let it go, and the engineer's just been back for another crack at sorting it out.

However, the tenant has told me that following the visit, he wase unable to fix the problem; but worse, the hot water will now only heat when the central heating's on; and the engineer says it looks like "new boiler" time.

Could anyone advise what the cause of the original problem might be? And also, what may have occurred to bring about the new issue?

On the one hand, it's quite an old boiler (~15 years?) so to be fair it isn't overdue for replacement; but on the other hand it's always been very reliable, and as it's on a service contract I'm naturally suspicious when I'm told a repair (ie at their cost) isn't possible, and that a new boiler (at my cost) is needed.

Thanks for any thoughts

[Bob Minchin]

When I ran my boiler on a UPS, I discovered that the flame detection (based on ionised gases changing a leakage path) relied on the Neutral supply being at or around earth potential. This comes naturally with mains supply but not with my UPS.

So maybe some sort of earthing fault? obviously you cant short E-N to test this but I found that a resistor around the 10s of Kohms sorted it out. Just a thought? Bob

[ARW]

The second fault would suggest that the diverter valve is to blame.

[Bob Minchin]

Agreed and absolutely no reason the engineer should suggest a boiler replacement although it might be long term cost effective for a distant rental property.

Bob

[Lobster]

Bob Minchin grunted in news:oq8uen$9hb$ [e-mail]:

Thanks guys that's really helpful. I can locate a diverter valve online for my model of boiler, too, so am prepared for the "sorry, can't get the parts for those any more" excuse!

I can't think of any reason why a dodgy diverter valve could be responsible for the original ignition fault though? Or conversely, how it stopped working during the fault-finding?

David

[Thomas Prufer]

Mail geoff at cetltd.

Even if it's not he's "done", he probably knows more about faults in old boilers than anyone else available.

Used to be a regular here, helpful.

Thomas Prufer

[Bob Minchin]

I feel these are two unrelated faults.

[Dave Liquorice]

might be?

Did it try to light but then shutdown? Thinking failing thermocouple. Assuming that it uses a thermocouple for flame detection. I don't know a lot about modern gas boilers, they might use some form of ion leakage through the flame?

conversely, how

Hum, "ham fisted" engineer knocking/breaking a wire off either directly involved with the diverter valve or it's associated control sensors/circuitry.

The bashing about has dislodged a lump of crud which is now jaming the valve?

[newshound]

IME you don't even have to be ham-fisted, the very act of looking for a known fault is quite capable of triggering an independent one!

:-)

[ARW]

Could you define your original problem in more detail?

When you said cutting out do you mean that sometimes it did not fire up in the first instance and went into lockout or that whilst giving heat or hot water it cut out?

I appreciate that you are getting second hand info from the tenant and are not there to do the tests yourself.

And have you had a look at

pages 18-20?. Yes I know you are paying a service contract but that does not always mean a lot.

[Lobster]

ARW grunted in news:oqbitu$mji$ [e-mail]:

Well things have moved on a bit now in that the the engineer came back and replaced the switch on the diverter valve, so the 'new' problem (ie HW only available when CH was on) is now cured, but unsurprisingly the original problem is indeed still present.

Tenant tells me that once it's up and running, the boiler is fine and won't cut out; but when it's cold and she turns the hot tap on it often just doesn't fire up and needs manually resetting. About daily, now.

Thanks, that's really helpful actually... I did already have a PDF manual but a much less detailed one without that fault-finding flow-chart. That's suggesting "Gas valve", "Safety thermostat", or fix the "continuity between the PCB control board and gas valve", depending on the exact symptoms. Sound about right? Neither of those parts are hugely expensive and I'm damned sure that if the boiler wasn't on a contract and it was me that had to pay for them, they'd have been replaced on the first visit. :(

Will be having words tomorrow...

[ARW]

So it's the ignition sequence that is failing.

You now have all the info I have, so all the best against them. You know know more than the engineer you pay for.