as the HW is working OK you can rule out the pump and the boiler
CH trips electric but hot water is ok - ????
- Thread starter Deby
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as the HW is working OK you can rule out the pump and the boiler, you say that the programmer was replaced can you remove it and post a pic of the wiring ?
It wasnt the Boiler PCB, there is a wiring fault somewhere
Think the boiler engineer was 'covering himself' by replacing it.. said it looked old and was probably ticking things off the 'possible cause' list one by one. So do you think it's wiring in the boiler or electrical wiring elsewhere in the house? It just seems really weird how it's been ok since I've been here (just over 2 yrs) and I believe the elements that were replaced were donkeys years old. We've not done any nails in walls where they shouldn't be (most of us know wiring runs vertically above light switches), not lifted any floorboards or things like that.. I know sometimes gremlins appear but it's just odd.. even more so as the HW is fine .. keep thinking surely I'm not that unlucky to be the only person in the world with a fault like this lol, just trying to do everything I can to help the tradesmen
I think you need a proper heating engineer
Ah right, ok - thank you for all your help and time, it is very much appreciated 
.. I will tell the estate agent, they asked me to update this post and let them know.. followed by a "wish all tenants were this helpful" - only helping the trades, good bunch of guys and to be honest it's annoying me too haha. Thank you
.. I will tell the estate agent, they asked me to update this post and let them know.. followed by a "wish all tenants were this helpful" - only helping the trades, good bunch of guys and to be honest it's annoying me too haha. Thank you 
I think you need an electriian rather than a heating engineer. Couple of worrying statements;
Well if that was true you could have free electricity. You haven't got solar panels or a windmill have you? How did the 'electrician' determine power was coming back in- wasn't with a glowing pen type device was it?
Since the hot water is functioning correctly, in your type of system the pump and boiler can be eliminated. So suspect items are the room thermostat, the controller, one wire in the 3 port valve and the wiring between them. The wiring to the room thermostat is only energised when CH is selected on the programmer. One wire in the 3 port valve is only energised when CH is selected. The CH wire leading from the programmer to the 3 port valve is only energised when CH is selected. It is quite likely that the room thermostat and the programmer and the 3 port valve are earthed via the boiler (explaining the remove boiler earth everything works sketch). So the fault will be there somewhere. Since the fault is heat sensitive, it'll most likely be in the wiring at or near the 3 port valve (was the cable from the valve head to the wiring centre replaced when the head was changed? If not that would be my favourite- check carefully where the cable comes out of the metal case covering it). If that's OK then next likely location will be under the floorboards where a cable has been left too near a hot pipe. An electrician with appropriate test gear will be able to narrow the fault location down quite quickly.
Whoever did that wasn't any sort of electrician.Please confirm that the boiler is in fact earthed
OK, that's feasable- any electrician with appropriate test gear should be able to fnd the fault- it is repeating in a predictable fashion
. Not necessarily true. Provided the boiler and pipework is earthed then yes a major fault to earth will blow the fuse/MCB but a minor fault might not (while still passing enough current to cause injury). As above please confirm that the boiler is in fact earthed. And please don't get that 'electrician' back (you may not have a choice as a tenant )
Well if that was true you could have free electricity. You haven't got solar panels or a windmill have you? How did the 'electrician' determine power was coming back in- wasn't with a glowing pen type device was it?
Since the hot water is functioning correctly, in your type of system the pump and boiler can be eliminated. So suspect items are the room thermostat, the controller, one wire in the 3 port valve and the wiring between them. The wiring to the room thermostat is only energised when CH is selected on the programmer. One wire in the 3 port valve is only energised when CH is selected. The CH wire leading from the programmer to the 3 port valve is only energised when CH is selected. It is quite likely that the room thermostat and the programmer and the 3 port valve are earthed via the boiler (explaining the remove boiler earth everything works sketch). So the fault will be there somewhere. Since the fault is heat sensitive, it'll most likely be in the wiring at or near the 3 port valve (was the cable from the valve head to the wiring centre replaced when the head was changed? If not that would be my favourite- check carefully where the cable comes out of the metal case covering it). If that's OK then next likely location will be under the floorboards where a cable has been left too near a hot pipe. An electrician with appropriate test gear will be able to narrow the fault location down quite quickly.
That is the fused spur for your heating , dont turn it off, it is not an immersion heaterI was told to never turn this switch off - and to be honest I'm not 100% sure if this is the immersion, sorry - it's a good job I have a desk job
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With DHW the boiler, and pump are running, with CH the boiler, pump and motorised valve is being powered, so it points to motorised valve or wiring to it. The valve is not powered for DHW.
6 - 7 minutes is a lot longer than it takes to open a three port valve, but I would be disconnecting the valve and testing insulation resistance, as that seems the most likely suspect. It is not a DIY fix, it needs equipment, I would start by testing the whole circuit on that RCD, and specially the neutral, intermittent faults are often traced to a neutral to earth fault, since neutral and earth are same voltage when there is no load, with no load even with a very low resistance it often will not trip, as load increases the voltage earth to neutral increases, so then the RCD trips.
So you can have a bit of damp bread in a toaster that causes the RCD to trip when kettle is used. You jump to oh kettle at fault, where it is really the toaster.
So trial and error does not work, you have to get out the meters and do it step by step, it could be nothing to do with central heating, but a faulty socket or cable and when the pipe gets warm it forces dampness through a wall or cable causing the trip, heat makes moisture travel, so with a meter able to push 500 volt through a cable the electrician will find the fault, the biggest problem is to ensure the test meter with 500 volt does not damage any electronics, often we turn them down to 250 volt and try with that first.
Proper name insulation tester, but most call them a megga, company name well know for making them, like calling a vacuum cleaner a hover.
So if I didn't have my megga, then since it seems to happen only with central heating, I would remove the head on the three port valve, or latch the head, and then switch on domestic hot water so central heating will get hot, but motorised valve is not being activated, so if valve faulty it will not trip, but if it is due to heat driving moisture then it will trip, so if with three port valve not activated it still trips, it is clearly time for an electrician with his tools to locate the fault.
I would also work out what else goes off, if the same RCD supplies sockets, then unplug anything plugged into those sockets.
6 - 7 minutes is a lot longer than it takes to open a three port valve, but I would be disconnecting the valve and testing insulation resistance, as that seems the most likely suspect. It is not a DIY fix, it needs equipment, I would start by testing the whole circuit on that RCD, and specially the neutral, intermittent faults are often traced to a neutral to earth fault, since neutral and earth are same voltage when there is no load, with no load even with a very low resistance it often will not trip, as load increases the voltage earth to neutral increases, so then the RCD trips.
So you can have a bit of damp bread in a toaster that causes the RCD to trip when kettle is used. You jump to oh kettle at fault, where it is really the toaster.
So trial and error does not work, you have to get out the meters and do it step by step, it could be nothing to do with central heating, but a faulty socket or cable and when the pipe gets warm it forces dampness through a wall or cable causing the trip, heat makes moisture travel, so with a meter able to push 500 volt through a cable the electrician will find the fault, the biggest problem is to ensure the test meter with 500 volt does not damage any electronics, often we turn them down to 250 volt and try with that first.
Proper name insulation tester, but most call them a megga, company name well know for making them, like calling a vacuum cleaner a hover.
So if I didn't have my megga, then since it seems to happen only with central heating, I would remove the head on the three port valve, or latch the head, and then switch on domestic hot water so central heating will get hot, but motorised valve is not being activated, so if valve faulty it will not trip, but if it is due to heat driving moisture then it will trip, so if with three port valve not activated it still trips, it is clearly time for an electrician with his tools to locate the fault.
I would also work out what else goes off, if the same RCD supplies sockets, then unplug anything plugged into those sockets.
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I have had with very old RCD's spikes on the line tripping them, however this would cause a random trip, not only tripping when central heating is used, I have on the odd time had a RCD which would random trip, but the RCD tester showed it as OK, and swapping the RCD cured the problem.
However your description of what the electrician has done and said, makes me think maybe he is not an electrician but some handy man who has a little knowledge of electrics, but is either out of his depth or lacking test equipment.
Years ago you found loads of electricians without the proper test equipment, but today the scheme operators require test sheets which can only be filled in after using the test equipment, so most today will have an RCD tester and insulation tester and loop impedance tester, they are often called 17th Edition test sets, not sure why still needed them for 16th Edition.
This is an immersion heater (the round thing at the top of the cylinder but yours could be on top or on the side) see if its wired to a switch, if we can find out why you have hot water it will help to find the fault,
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