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?

 

[Wilko]

Hi - if I’ve understood correctly, the problem ONLY happens when the boiler runs (?) as you've mentioned an immersion is used in summer to heat the HW. If so, then I’m thinking it might be worth insulation resistance testing the circulating pump.

 

[Ian Mills]

I had a customer with same problem the electric would trip but when I got there problem had gone, turned out to be a pipe and cable passing through same hole and the cable had the insulation strip off it as it had been put in, would only show fault when pipes where expanding when up to temp would be okay

 

[HappyHippyDad]

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

An intermittent fault can be a right pain to track down. The electrician you hired may have been good at fault finding or may not. How long roughly did they spend with you? Could you state some of the actual results they found? It would help immensely if you had insulation resistance results for each circuit, otherwise I think it's unlikely anyone is going to be able to diagnose your fault on line.

 

[radiohead]

An intermittent fault can be a right pain to track down. The electrician you hired may have been good at fault finding or may not. How long roughly did they spend with you? Could you state some of the actual results they found? It would help immensely if you had insulation resistance results for each circuit, otherwise I think it's unlikely anyone is going to be able to diagnose your fault on line.

Agree, without knowing what the original electrician found or tested and his/her experience in the art of fault finding it's just guessing. I would ask a second electrician to take a look. To me this sounds like a simple N-E fault somewhere on the installation. Of course there is every chance it may be more complicated as well.

 

[Dabbers]

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





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.

Have you tried running hotwater only without the central heating on and if so does the fault occur then?
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Ok so i have been pondering over this and one thing that springs to mind is " where is the NEUTRAL connected from the rcbo " the FLy lead from the RCBO is it connected into one of the neutral bars that the affected RCD is into if this is the case then this will happen as the RCD is seeing an imbalance.. if you look closely at the picture the fly lead should be over on the far right hand neutral bar and the RCBO should be installed right next to the main isolator switch and the bus bar should be connected directly to the main incoming switch if it is not then this is more than likely your fault.
if your fuse board is not as described please send a pic!

 

[Dabbers]

Before I go any further can you tell me where the RCBO is in the DB is it next to the Main switch? i'm wondering if it has been positioned on the busbar which is controlled by the rcd the easiest way to determine this is the switch off the RCD and see if you still have power to the heating system. a picture speaks a thousand words? please let me know of your findings.

 

[Lucien Nunes]

This is a curious point.... It's so fundamental it would be easy to overlook. If the RCBO has been put on the RCD protected side by mistake, then a modest amount of leakage from the heating system would still tend to trip the RCD before the RCBO due to the additional leakage from the rest of the installation.

It seems unlikely that only the RCBO's neutral would be in the wrong busbar as mentioned earlier, because any heating system load should then cause an immediate trip.

 

[Dabbers]

This is a curious point.... It's so fundamental it would be easy to overlook. If the RCBO has been put on the RCD protected side by mistake, then a modest amount of leakage from the heating system would still tend to trip the RCD before the RCBO due to the additional leakage from the rest of the installation.

It seems unlikely that only the RCBO's neutral would be in the wrong busbar as mentioned earlier, because any heating system load should then cause an immediate trip.

My thoughts were the live on the wrong bus bar or neutral in the wrong bar could well be causing this issue I have seen this before the biggest trouble is that the load is very minimal on the heating system.

 

[Markyd]

This is why I asked for a pic 4 days ago

 

[L.F.]

Many apologies for not responding for several days but I've been diverted onto other domestic issues! The consumer unit is not very obvious to follow so I've drawn a schematic to show how it all fits together. It has been modified because originally it was thought that the central heating was causing the tripping problem, so it was put on an RCBO. That didn't cure the problem, so Sockets 2 was moved onto a separate RCD. By the way, MCBs on the Sockets 1 RCD include the fridge, cooker and freezer. The only other item on the Sockets 2 side is the Photovoltaic panels.

I am convinced the Sockets 2 RCD tripping is indirectly connected to the central heating. It trips every day now, between half an hour and an hour after the c/h comes on.

I'd be really grateful for any further suggestions I could discuss with the electrician when he comes later this week.