Ideal Classic Boiler Problems - Help Please

lintdrummer

Bare with me here, it's a long story.

Back in mid January I started having issues with the RCD on my fuse board tripping randomly. Eventually realised it was coinciding with the boiler coming on. It's an Ideal Classic FF gas boiler, probably 20 years old. Running a Tado smart heating system here too. All had been working well for over a year at this point.

Called a local RGI plumber who gave excellent info over the phone but wouldn't be available for a good few days so he gave me a couple of recommendations. Called one, a large Dublin based company, who also said it would be a few days but they booked me in for an appointment later that week. Tried the other recommended plumbers in the mean time but nobody could get to me sooner.

So plumber comes out and has a look and says all appears to be in order, apart from the fact that the RCD is tripping for unknown reason, definitely seems to be connected to the boiler though. Not necessarily happening at any one stage (eg. ignition or fan kicking in), sometimes heating could be on 15 mins before the RCD tripped. But with boiler physically switched off, I have no problems.

Guy says only thing he can think of is faulty circuit board so we'll try replacing that. I've had a couple of other small electrical issues before the RCD problem started so he recommends getting an electrician to check the house and make sure no underlying fault there.

I get an electrician out and he checks the wiring with a Megger. All good, no leakage or underlying problems. Upgraded the RCD to more modern unit just to rule that out.

Plumber gets back eventually with a circuit board. Fits it, all seems well. Waits about 15 mins and no problems. He goes and about 5 mins later RCD trips.

Call him back but he's already booked for another job so he can't come back to me. It's about 4 or 5 days later he gets back and tries bypassing the high limit stat. Seems to work. So he says he'll order replacement stat and get back out.

So this does fix the problem, I've heating but the safety of the stat has been bypassed. Only last Thursday he got back out to replace the stat. All was well until I woke up this morning, RCD tripped, and I'm back to square one.

We went about 3 weeks back in late January, early Feb with no heating. I can't face into that again now, especially since we're stuck at home.

Can anyone offer any advice or tell me what they think might be going on here exactly? I've called the plumber today but no answer. I'm pretty certain they do no call outs on Sunday's anyway but I'd really rather not go without heating tonight.

It's probably worth mentioning that the high limit stat reset switch never pops out, either on the old one or the new one that was fitted.

Wearb

I've seen this on an oil boiler. It was caused by a faulty circulating pump. Worth looking into.

lintdrummer

Wearb wrote: »

I've seen this on an oil boiler. It was caused by a faulty circulating pump. Worth looking into.

Thanks for the suggestion. Would this make sense even though bypassing the high limit stat solved the problem for so long?

Wearb

lintdrummer wrote: »

Thanks for the suggestion. Would this make sense even though bypassing the high limit stat solved the problem for so long?

It is intermittent, so don't rule it out.



Was there any test carried out on the circ. pump? btw not sure if you can use a megger on them.

lintdrummer

Wearb wrote: »

It is intermittent, so don't rule it out.



Was there any test carried out on the circ. pump? btw not sure if you can use a megger on them.

To be honest the plumber that came out never had anything more than a multimeter and basic tools with him, he seemed convinced that all individual parts of the boiler were working as intended. I didn't see him carry out any specific tests as such. The only thing we noted was that the fan ran on the timer from Tado, even with the boiler switched off, and that never caused a problem on it's own so we ruled it out as the cause.

Edit just to say that the electrician meggered all the wiring in the house from the fuse board, he did not go at the boiler with it.

lintdrummer

Just to update, plumber was back this morning and pulled the high limit stat out of the housing. All was well again for a couple of hours but now the RCD has tripped and unlike anytime before it will not reset. So now I've no heating and no electricity. Have tried calling a couple of other plumbers for a second opinion but no answers.
I've also switched off the boiler, and one by one plugged out all devices around the house to try and get the RCD to reset, in case it was something else causing it, but no joy.

Edit: I've managed to get the RCD to stay on by going through individual breakers on the fuse board. Unfortunately all unlabeled. 3 breakers next to the RCD, if I switch any of them on the RCD trips.

John.G

Have you tried replacing the RCD even if it seems unlikely?

Can you break the neutral from the boiler, you may have a neutral to earth fault.

Also, if you have a multi meter, with the RCD tripped, test the resistance on a number of plug sockets between neutral and earth.

Edit: I see you have replaced the RCD.

lintdrummer

John.G wrote: »

Have you tried replacing the RCD even if it seems unlikely?

Can you break the neutral from the boiler, you may have a neutral to earth fault.

Also, if you have a multi meter, with the RCD tripped, test the resistance on a number of plug sockets between neutral and earth.

Edit: I see you have replaced the RCD.

Have a cheap multimeter somewhere, will have to fish it out. When you say break the neutral from the boiler, are you talking about physically disconnecting it at the main feed to the boiler circuit board?

John.G

Yes.
Then try resetting those 3 breakers.

lintdrummer

John.G wrote: »

Yes.

Will try that and report back.

lintdrummer

You sir are a lifesaver! Disconnected the neutral feed and all now works. So what does this tell me about my problem?

Wearb

MOD NOTE: I am going to move this whole thread to electrical. It's obvious now that it's the best place for it. Some good diagnostics people there
I leave a link for anybody following.

John.G

lintdrummer wrote: »

You sir are a lifesaver! Disconnected the neutral feed and all now works. So what does this tell me about my problem?

I would try and narrow it down, see where you can disconnect any neutrals local to the boiler, ie, neutral from the circ pump, neutral from the boiler stat(s), neutral from the fan/burner or/and any others you can think of and then reconnect the main neutral, reset your rcd/breakers and then start reconnecting the above neutrals, checking after each. It might be no harm either to have a small electrical load from anywhere on while doing this which will give a fault current to earth and trip the RCD which otherwise it may not.

See page 7 of attachment for some of a typical burner neutrals.

Edit: got mixed up there, between a oil/gas boiler!!. so attachment of no help really.

Bruthal

lintdrummer wrote: »

You sir are a lifesaver! Disconnected the neutral feed and all now works. So what does this tell me about my problem?

Where did you disconnet it?

lintdrummer

Bruthal wrote: »

Where did you disconnet it?

The main feed comes in through the high limit stat, handy because it runs through a simple junction box there and was very easy to disconnect.

lintdrummer

John.G wrote: »

I would try and narrow it down, see where you can disconnect any neutrals local to the boiler, ie, neutral from the circ pump, neutral from the boiler stat(s), neutral from the fan/burner or/and any others you can think of and then reconnect the main neutral, reset your rcd/breakers and then start reconnecting the above neutrals, checking after each. It might be no harm either to have a small electrical load from anywhere on while doing this which will give a fault current to earth and trip the RCD which otherwise it may not.

See page 7 of attachment for some of a typical burner neutrals.

Edit: got mixed up there, between a oil/gas boiler!!. so attachment of no help really.

Great, it all runs through the board after the high limit stat. Should be easy enough to trace from there to each component. I have an electrician organised to come over later so he'll do some troubleshooting of individual components I expect.

Bruthal

Test between N and E at the boiler with megger would be one check.

A dedicated RCBO on the boiler circuit if it is run direct from the board as well might be an idea.

lintdrummer

Update: The electrician called over yesterday and quickly traced the problem to the fan on the boiler. Initially he thought the windings in the transformer on it were possibly degraded and causing internal short but it seems the problem was much simpler; there were two wires going into the fan which had been fiddled with and cut at some unknown stage (likely pre my buying the house) and these were bare of insulation just where they meet the pump. He wrapped them and lo and behold the problem has gone away. They must have been shorting off the casing.

Might explain why the problem was intermittent, if the cover had been off the boiler, the wires may have been moved in such a way that they weren't contacting anything. Then when the plumber comes back to replace a part they end up touching the case and shorting.

Will keep an eye on it but if the problem reoccurs, the fan will be the first thing to get replaced.

John.G

Glad to hear you are sorted out, probably lucky in a way that both live & neutral were bare, but surprising that the relevant MCB didn't trip at some stage if the live was shorting out, its hard to imagine the RCD tripping before the MCB but maybe possible under certain conditions.

Bruthal

If the phase contacts the earthed frame, only 30 or so ma needed to trip the RCD instantly. 10 amp mcb might need 15 to 20 to trip relatively instantly. So it can happen that only the RCD trips even with slight phase to earth faults.

N to E contact happens, only the RCD might trip.

If the mcb is not tripping, it does point to N to E fault alright though.

John.G

My Hager 40A/30MA RCBO seems to have short circuit protection as well as o/load & earth tripping, can you explain this please and does a MCB have the same? (apart from earth leakage tripping).

Bruthal

John.G wrote: »

My Hager 40A/30MA RCBO seems to have short circuit protection as well as o/load & earth tripping, can you explain this please and does a MCB have the same? (apart from earth leakage tripping).

40 amp RCBO is an MCB and RCD in one unit.

Overload protection is when the load goes over 40 amps. 41 amps and probably wont ever trip.

There is a curve to show expected trip times. At 1.5 times the rated current, 60A for a 40A mcb, it might take a minute or so to trip.

At 3 to 5 times the rated current, a B type MCB should trip more or less instantly. That is where short circuit protection comes in.

So they are not precision instruments, but are good enough to protect cables.

Phase to Earth tripping will be like a short circuit but depending on how good the short connection is, the RCD will be far more sensitive to this, and might trip before the MCB gets a chance to.

N to earth causes some current to be missing on the Neutral, so the RCD part trips if there is a load in to cause current to divert.

Some might be more up to speed on the curves, i havent dealt with them much in recent years, not those types of curves anyway:eek: