New boiler tripping RCD

[TheGovernor]

Hi all,

I'm looking for general advice how to approach this as I have a very annoying intermittent problem with our new boiler, fitted a fortnight ago.

Just to describe the system, we've got a Vaillant Ecofit 425 and we had a Gledhill Stainless vented Cylinder fitted at the same time, it's a conventional system (cold storage in the loft, header tank for the central heating)

Our problem which has started occurring the last few days is that the heating has been tripping the RCD but completely randomly at different times of day, it can run fine for 15+ hours and then suddenly trip.

The only way I can get the power back on when it does trip is to turn the power off to the boiler at the wall switch, switch the main board back on, then switch the heating power back on and quickly set the water/heating to off at the controller before it trips again.

Initially I suspected it was the pump, but the more I think about my process the more I think it's the boiler.

Reason being is that when I get the power back on, as long as I've set the CH/Water to Off at the controller, the pump will still run (like it does when it overruns) which seems to indicate the pump is okay. This leads me to think it's me stopping the boiler heating that stops it tripping... it tripped last night at 0100 when there was barely any other power being used in the house.

I've spoken to the fitter who's a bit stumped, he suggested calling Vaillant or an electrician, on the basis an electrician isn't likely to get inside the boiler I've decided to call Vaillant out. I don't know what these guys are like for diagnosing intermittent faults so I'm a bit worried they'll turn up, won't be able to get it to trip and then bugger off...

At the moment we're having to set the controller to off for water/CH overnight to avoid it tripping the RCD while we're asleep... so it's a bit of a pain

Sorry for the war & peace, I'm just looking for insight from the experts here as to what might cause the RCD to trip after such long periods? Hopefully my process above makes sense and is logical.

 

[cross thread]

Check around the zone ,diverter valve and wiring centre to see if any signs of a small leak

 

[ianmcd]

post pics of your wiring at controls and boiler ends

 

[TheGovernor]

Thanks for the assistance guys

Check around the zone ,diverter valve and wiring centre to see if any signs of a small leak

I can't see any sign of water escaping anywhere at the moment... although I can't see inside the boiler...

post pics of your wiring at controls and boiler ends

There not a lot to see as you can tell from the attached pics, is this what you meant? (Ignore the white cable with the two wires that's a separate supply to a downlight)

 

[bernardgreen]

Does it trip the RCD when the boiler fires up and the ignitor is sparking ?

The spark to ignite the gas is created between the spark electrode and the metal work of the gas burner. The gas burner is Earthed via the pipe work and as such the current in the spark is going to Earth. This "leakage" of current to Earth may be enough to trip a sensitive RCD.

It was a problem with the boiler in my daughter's first house and the only way to remove the problem was to move the boiler power supply to a non RCD circuit

 

[TheGovernor]

Does it trip the RCD when the boiler fires up and the ignitor is sparking ?

The spark to ignite the gas is created between the spark electrode and the metal work of the gas burner. The gas burner is Earthed via the pipe work and as such the current in the spark is going to Earth. This "leakage" of current to Earth may be enough to trip a sensitive RCD.

It was a problem with the boiler in my daughter's first house and the only way to remove the problem was to move the boiler power supply to a non RCD circuit

It's hard to tell, as it will generally trip while we're in the lounge watching telly or something, like I said in my initial post, it seems like stopping the boiler firing is what allows me to get the electric back on, so it's possible it's a similar problem to the one you described... interesting solution taking it off the RCD, is that an okay thing to do?

 

[RandomGrinch]

Does it trip the RCD when the boiler fires up and the ignitor is sparking ?

The spark to ignite the gas is created between the spark electrode and the metal work of the gas burner. The gas burner is Earthed via the pipe work and as such the current in the spark is going to Earth. This "leakage" of current to Earth may be enough to trip a sensitive RCD.

It was a problem with the boiler in my daughter's first house and the only way to remove the problem was to move the boiler power supply to a non RCD circuit

I'm only a DIY'er, so I'm not suggesting that this is the issue. But as above, a friend has had a similar problem.
Their FCU was on a damp wall; the backbox and wiring was badly corroded - seemingly random trips occured when the ignition attempted to fire, through a poor path to earth.

Although, there may be some things you can do to rule this out?
As the leakage to an RCD can add up from other appliances on the same circuit; you could try turning things off that may otherwise be left on?
It might also be possible to temporarily wire a plug onto the boiler, and run it on an extension lead from a different circuit?

Hopefully, others with more experience can suggest if these options are worth trying!

 

[Deleted member 267285]

Is it the rcd or mcb? If it’s the former, then how do you know it’s the boiler? (A bit like what Random Grinch mentioned).

 

[TheGovernor]

Is it the rcd or mcb? If it’s the former, then how do you know it’s the boiler? (A bit like what Random Grinch mentioned).

It's an RCD... the reason I think that is that when it trips unless I switch the heating circuit off at the spur, I can't switch the electric back on, plus it happens almost regardless of what else is on or off in the house, I know it *might* be something else but it seems too much like a coincidence having had the new boiler put in recently.

Funnily enough, the boiler was just running, I changed the water from Constant to Twice while the boiler was on (in cycling mode I think it's called, when it has enough heat and its just circulating) and the RCD tripped again. So again, it *could* be the controller, but again, the only recent change is the boiler...

 

[Hairymelon]

The most cost effective stab in the dark is to try a new pump ( assuming it wasn’t replaced when the boiler was fitted.). It’s a component where water and electricity are in close proximity seperated by a seal

 

[TheGovernor]

The most cost effective stab in the dark is to try a new pump ( assuming it wasn’t replaced when the boiler was fitted.). There isn’t another component where water and electricity are in close proximity seperated by a seal

I must admit that was my initial thought...

 

[TheGovernor]

More tripping last night and today, today's one was a bit encouraging in a way because it seems to confirm an earth leak (or overload) on the Kitchen circuit.

The wife had the fan-oven on and was boiling the kettle and when I turned the hall thermostat up to get the boiler to fire the RCD tripped again... so it does seem like the heating is at the center of it all (whether it is the boiler or other controls is still not 100% clear). I have a small inkling that it happens when the boiler is already hot but haven't proved that out yet, everything take so much time to do waiting for things to heat up/coll down etc etc.

I've got an electrician booked to come today through BG Homecare, I am hoping based on what happened this morning a leak will be more obvious than I had at first feared...

 

[Deleted member 267285]

How soon after you adjusted the thermostat did it trip?

 

[Terrywookfit]

Have the installers " Borrowed " a neutral from another circuit.

 

[ericmark]

It is hard to isolate the problem without test gear. Last house had loads of things on one RCD and could run for 2 years no problem, then trip 10 times in a week, no fault found and another 2 years trouble free.

As a result this house all RCBO which is a RCD and MCB combined, so any fault limited to one circuit.

As an electrician I have three tools to help me, or at least should have.
1) Insulation tester - this puts 250/500/1000 volt depending on selection between two points and it measures the resistance, this is the main tool, but failed to find any fault with it in my own house.
2) The RCD tester - this normally puts 15 mA, 30 mA, 150 mA on the RCD to show it will not trip too soon, will trip at 30 mA and will trip in 40 mS at 150 mA all tests done with both positive and negative half cycles so 6 tests in all.
3) Clamp on ammeter - this is used to see what back ground leakage there is during normal operation, should be less than 9 mA, I have never done this test, as don't have a meter which will go down to 9 mA.

The problem is where there is a neutral to earth fault, as this can point to the wrong item, in the main one thinks the fault is some heavy current user, where really it is some light current user and the heavy current user has caused the voltage between earth and neutral to increase and so cause the trip.

I hope the BG Homecare electrician has now found your fault, however you must ask yourself is it worth changing the set up and using all RCBO's rather than a RCD shared by many circuits? When I put two RCD's on the last house, you could not get single width RCBO's, so I had no option, loosing a freezer full of food just before I moved, made me fit all RCBO's to reduce the risk, and when my roof leaked, I lost just a few sockets which I could do without.