Oil fired CH boiler trips main RCD to whole house.

[Marls]

Hello!

i hope someone can help please as we are now desperate. 
We’ve now had 3 electricians and one plumber look at this and no one can seem to find the cause and fix it.

We have an old oil fired boiler, it’s been serviced every year and seems to be functioning well. As a result of this problem, most of the Electrical components have now been replaced.

The problem started last autumn when we switched the central heating back on (we don’t have it on from about April to September each year) nothing had been changed in between it being switched off in the spring.

Th boiler fires up and then the main RCD to the whole house trips after a VARIABLE amount of time. Sometimes it’s less than 5 mins and other times it’ll run for over an hour.

The weird thing is that if we isolate the boiler by turning off the main fuse to it (and switching it off) the RCD will often continue to trip. However this is not consistent. Sometimes the RCD can be switched back on straight away. 
If we turn off other fuses to different  circuits, there seems to be no pattern as to whether it will work.

I’ve had a theory that the immersion heater had something to do with it, as I had heard it boiling just before this all started (we use the immersion for hot water in the summer).

None of the electricians thought this was a problem but one changed the flex going to the immersion. Since then, the neutral wire has burnt out twice - seems to have overheated. I changed the immersion thermostat as we are in lockdown and can’t get an electrician now-had no hot water or heating. The neutral wire burnt out again and now the immersion is not working at all. 
I isolated it completely by disconnecting all the wires to the immersion and tried the boiler again. Thought it was fine as it went for two hours- roughly until the hot water was at temperature, then tripped main RCD again.

Th plumber has serviced the boiler, replaced the Heating pump, the hot eater thermostat on outside of the tank, the valve that diverts HW or CH, the starter thing in the boiler and the burner. 
The electricians said they don’t know what the problem is.

We’ve had no heating all winter and now no hot water-would be really grateful for any suggestions. Thanks

 

[Murdoch]

When you say the main rcd, is this the only rcd? Or are there others?

does this trip if you just run the heating? Just run the water? Or both?

 

[ProDave]

Not very good electricians then?

I would have started by suggesting reconfiguring the CU to put the boiler on it's own rcbo.  Oh and a full test of the other circuits for earth leakage.

 

[Geoff1946]

The neutral of the immersion "burning out", with a new heater can ONLY be due to the connection not being properly made. Perhaps the old cable was oxidised?   Try again, preferably with a new piece, either cut back or replaced. At least that will give you hot water.  Your other problem requires an electrician with test gear.

Sorry, just  re-read it, only the thermostat changed, not the actual heater.  I would replace the lot.

 

[Evans Electric]

Immersion heaters are notorious for breaking down and tripping RCDs   ,  even more so in hard water areas .    Tests need carrying out by  the electrician ,  your oil fired boiler sounds like everything has been renewed by now .

Immersion heater needs testing  properly , not just the stat . 

That main RCD needs to be tested  .    Why does it switch EVERYTHING off ?   Are you out in  a rural area or a city ?      Certainly need looking at changing or rehashing the consumer unit  to reduce the nuisance  tripping  .  

 

[Murdoch]

Hold on, the op suggests the rcd trips when they are using the boiler to heat the water ....

so back to basics ...

get a better spark onsite

op - where are you based

PS if you have a single upfront rcd the issue could be anything, even commulative earth leakage ,....

 

[NozSpark]

TBH it doesn't sound like your boiler is at fault.... it could be all sorts of other things from being an old immersion element to being a cable trapped between a pipe and joist

IMHO your wiring needs to be methodically tested

 

[UNG]

Are you sure the three electricians that have looked at this actually were electricians as I'm sure any decent electrician would have found the fault

As Murdoch asked where are you located it may be someone on here is close to you and will take a look