RCD tripped by central heating which is on a separate circuit

[L.F.]

My central heating is on a dedicated RCBO. The house has two other RCDs, one including the fridge, freezer and cooker. The other RCD is tripping virtually every day after the central heating has been on for 40 minutes or so. It will then often trip again after a few minutes. It can be reset and then it won't trip again until the next day. However, if I let the house temperature drop it will trip again once the central heating has been on for 40 minutes or so. It doesn't trip in the summer. It's driving me mad. Any ideas please?

 

[telectrix]

wild gues. could be cable/s (maybe with damaged insuluation) touching a hot pipe. when the pipe heats up from the c/h, the fault appears

 

[L.F.]

wild gues. could be cable/s (maybe with damaged insuluation) touching a hot pipe. when the pipe heats up from the c/h, the fault appears

Thanks, that has been suggested before. It does seem to be linked to heating the house from a lower overnight temperature as it doesn't trip when the heating periodically comes on to top up the temperature again during the day.

The following items are on the affected RCD circuit - TV, Sky box, hi-fi, various floor lamps, phone, alarm, shredder, laptop (when charging), phone booster, outside light, PC, printer, router, radio. It doesn't trip if I disconnect all of them (which perhaps suggests that it isn't caused by a cable touching a hot pipe), but I can't identify which, if any, item is causing the problem. Any combination of items connected results in a trip.

 

[telectrix]

with all the rain recently, water in outside light (or junction box/es) is a prime suspect

 

[Wilko]

Hi - you mentioned that it doesn’t trip in summer ... does that mean you had the same issue last winter, but it didn’t happen last last summer. Or does it mean this is a new problem that has just started to happen?
Also, how is your hot water heated please?

 

[Ned Gibbons]

Have you checked that the RCBO is connected directly to the main switch and not via RCD.

 

[radiohead]

Without any testing being carried out it's a guessing game.

 

[Lucien Nunes]

Thermal movement causing the fault to come and go is not contrary to your observation that unplugging the loads stops the tripping, if it is a neutral-earth fault. These often manifest as circuits that only trip under load, even when the loads themselves are not faulty. N-E faults can be influenced by loads on other circuits, so the time of day and season might affect the tripping threshold if circuits on the other RCD are more heavily used at certain times. However, it will always be the RCD that protects the faulty circuit that trips.

 

[Markyd]

can we get a pic of the consumer unit

 

[Dabbers]

ok firstly is this a combi boiler or a system boiler? have you got a big green water tank or white one? if you turn you hot tap on does the boiler fire up and give you hot water?, do you have solar panels and a Immersun?

 

[L.F.]

with all the rain recently, water in outside light (or junction box/es) is a prime suspect

Thanks for your suggestion. However, the fault has existed for two years, but it's getting worse.

 

[freddo]

Best call an electrician, likely quite quick to locate the problem with an insulation resistance tester.

 

[L.F.]

Hi - you mentioned that it doesn’t trip in summer ... does that mean you had the same issue last winter, but it didn’t happen last last summer. Or does it mean this is a new problem that has just started to happen?
Also, how is your hot water heated please?

The problem was there last winter too, although not as bad. No problems over the summer until we turned on the c/h.

ok firstly is this a combi boiler or a system boiler? have you got a big green water tank or white one? if you turn you hot tap on does the boiler fire up and give you hot water?, do you have solar panels and a Immersun?

We have an oil-fired Worcester Greenstar Camray condensing boiler. It is a fully pumped system with two motorised valves, one to the rads and the other to the coil in the h/w cylinder. In the summer we use the immersion heater, and turn off the boiler. We have PV panels and they help heat the hot water via an iBoost unit which diverts power to the immersion heater if we're not using the all electricity being generated.

 

[L.F.]

Best call an electrician, likely quite quick to locate the problem with an insulation resistance tester.

I have and he's done extensive tests. The problem is that it's intermittant.

 

[freddo]

Oh whoops, I missed that.