Hi. 3 wks ago, my heating came on through the programed timer. 6-7 minutes later the electric for the whole house went out. The distribution board was old with only one RCD which was extremely 'dodgie'. This has now been replaced but same thing is happening. Over these 3 weeks the electrician, plumber and boiler engineer have also replaced the valve header unit, the water cylinder thermostat, the boiler PCB board, the program timer box in the airing cupboard and have fully tested the boiler, wall thermostat and electrics.. but still the same issue. A temporary fix is that the CH is now 'disconnected' from the RCD and when the electrician turned all the power off, power was coming back into the property (?) Electrician is now contacting the power company to see if it is 'tripping' outside. Could the fault lie with the motorised diverter or the pump - other forum feeds have mentioned this. Interestingly, when the earth within the boiler was disconnected the CH was all ok and running for well over 20 minutes, but when connected back up the CH was tripping the RCD within the 6-7 minutes again. After 3 wks of nothing from my estate agent who manages the property for their landlord I am getting rather desperate for some help! Any ideas please?. Thank you
CH trips electric but hot water is ok - ????
- Thread starter Deby
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D
Deleted member 267285
I’d possibly be looking at earth continuity, resistance values, insulation resistance. Have you nicked any cables, eg screwed any floorboards down, or put pictures up? Had a fault once where electrician suspected the boiler, turned out to be a nail in a cable.
Hi, thanks for your post. I will have to ask the electrician about the earth continuity, resistance values, insulation resistance. As far as nicking cables, I've done nothing like you describe in the past few months. Been here just over 2 yrs and this is the first time this has happened. One day fine next came home from work to a dark house, thought it was just a normal power cut. Took me a few hours to figure out it was the heating tripping the electric. Worried about the CH being disconnected from the RCD - could the amp leak not electrify the pipes?
Did the boiler engineer not disconnect power going to the pump? They can be cause of electric tripping and often will do so after short while running.
Anything with a motor in it is a suspect and especially a pump as it also obviously has water.
Anything with a motor in it is a suspect and especially a pump as it also obviously has water.
D
Deleted member 267285
I misread the post, thought pump head had been changed but think this must have been referring to the zone valve head. Yes could be the pump.
I noticed the OP said the valve head was replaced, so thought maybe pump. Strange if it wasn’t checked.
I am not an electrician, but when I get call outs to oil boilers blowing fuses or tripping, the circulating pump is first suspect and then burner motor.
I see a lot of pumps that the seals inside have gone and let some damp into electrics.
D
Deleted member 267285
I’m not electrician either
I just thought because a plumber had been it was checked 
#Naive. I go to a fair few gas combi boilers where they have got water into the housing because seals have gone.I’m not electrician either
Just checked your profile. Hadn’t realised you are a plumber and gas engineer.
You would have a good knowledge of electrics though.
I am only oil install/servicing or solid fuel work, plus normal plumbing work.
The old sealed motors like SMC that moved the impeller by magnetic action were hard to beat. No water could get into motor.
which boiler do you have ?
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I wonder why an electrician has not tested to find out what is faulty, for a RCD to trip, the current in does not match current out, in the main this means some current is going to earth, however as @ianmcd is asking some boilers have electronics which means there is a DC component to the current so a type A rather than normal type AC RCD is required, I know Worcester Bosch ask for a type A with some of their boilers.
Also in many houses there are many circuits powered with same RCD, in my case I have 14 RCBO's which is a RCD and MCB combined, so when one circuit fails it does not affect others, but where one RCD feeds many MCB's then it is a case of getting the insulation resistance meter out and actually test, as many items can all have a slight leakage, and the central heating may be just the straw that breaks the camels back. There is also a clamp on meter, but for the clamp on meter to work, it needs to be below the trip threshold.
The RCD should always be testing when changed, the strain on the cables can cause it either not to trip, or trip too easy, so the RCD is tested 6 times, three tests but each done on both positive and negative half cycle, so check it does not trip on half rating (15 mA) then check does work at rating (30 mA) then test at 5 times rating and must trip within time (40 mS) clearly can't measure 40 mS with a stop watch, so needs proper meter, this testing must be done when a RCD is changed. However I have seen where a RCD is tripping and it passes all tests, but swap it and new one passes all tests but does not trip.
However it is not cured by randomly swapping parts and crossing fingers.
Fact it does not trip with earth disconnected does point to the boiler, unless disconnecting boiler earth also means earth disconnected from some thing else. There are signs on the RCD
this one means type AC which is standard, but
this means type A which some boilers require. Even with RCD's of same type, not all equal, there are some which give a warning first then trip at 90% instead of 50% unfortunately they called them X-Pole so when you hunt on internet you get pole dancers.
I did get a rubbish electrician at mothers house, all he had was a multi-meter, clearly not a scheme member as they are forced to have all the test equipment, from what you have said it seems the electrician either does not have the test equipment or does not know what he is doing? Because it needs calibrating it is normally supplied by the company, not personal tools, and some companies are tight, and make electricians share the equipment.
Also in the main items are tested using 500 volt, however this can damage some items so we also have a 250 volt setting for sensitive items like a boiler, so the guy does need to know what he is doing, the 500 volt will not kill you as very low amps, but it would give you a nasty shock, so normally electricians work in pairs where doing inspection and testing.
Also in many houses there are many circuits powered with same RCD, in my case I have 14 RCBO's which is a RCD and MCB combined, so when one circuit fails it does not affect others, but where one RCD feeds many MCB's then it is a case of getting the insulation resistance meter out and actually test, as many items can all have a slight leakage, and the central heating may be just the straw that breaks the camels back. There is also a clamp on meter, but for the clamp on meter to work, it needs to be below the trip threshold.
The RCD should always be testing when changed, the strain on the cables can cause it either not to trip, or trip too easy, so the RCD is tested 6 times, three tests but each done on both positive and negative half cycle, so check it does not trip on half rating (15 mA) then check does work at rating (30 mA) then test at 5 times rating and must trip within time (40 mS) clearly can't measure 40 mS with a stop watch, so needs proper meter, this testing must be done when a RCD is changed. However I have seen where a RCD is tripping and it passes all tests, but swap it and new one passes all tests but does not trip.
However it is not cured by randomly swapping parts and crossing fingers.
Fact it does not trip with earth disconnected does point to the boiler, unless disconnecting boiler earth also means earth disconnected from some thing else. There are signs on the RCD
I did get a rubbish electrician at mothers house, all he had was a multi-meter, clearly not a scheme member as they are forced to have all the test equipment, from what you have said it seems the electrician either does not have the test equipment or does not know what he is doing? Because it needs calibrating it is normally supplied by the company, not personal tools, and some companies are tight, and make electricians share the equipment.
Also in the main items are tested using 500 volt, however this can damage some items so we also have a 250 volt setting for sensitive items like a boiler, so the guy does need to know what he is doing, the 500 volt will not kill you as very low amps, but it would give you a nasty shock, so normally electricians work in pairs where doing inspection and testing.
Hi all, thank you so much for all your posts.. Update, still not resolved. I spoke with the estate agent's electrician about the pump - if a seal had gone causing water to leak onto the electrics. He said he didn't think it was the pump because we have hot water.. the motorised diverter was the value header I was trying to explain and that has been changed. The electrician said something about mains electric "coming back in" when he disconnected the power completely (not sure what he means by that) and since everything possible has been replaced, thoroughly checked and tested and since we have hot water (heated by the gas boiler and stored in the water tank) no one knows where the amp leakage is - The NIC board were stumped too and that's why the electrician asked if the power company had completed any works recently as it maybe tripping outside. The local distributor (Western Power) came round this evening and could only perform "simple tests/checks" and according to them, everything is fine with their end. So we seem to be back at square one. For the record we have a Potterton boiler - which I know has a bad rep. We are still in the "it's the boiler - no it's the electrics" phase and think trades are confused as we are getting hot water from the boiler no problems at all, it's purely when the central heating kicks in. Also to note, I was told that even though the CH is disconnected from the RCD the pipes won't get electrified as the fuse would blow first - ?. It's frustrating as I have to go through the monkey to speak with the organ grinder, have no idea what people are on about as I'm just "jo blogs" (lol) and things get a bit "chinese whispers". So if anyone does have any further suggestions I'd be very grateful and can pass them on. Thank you
post a pic of the valve head you mention
This is the airing cupboard set up. The water tank thermostat 'whitebox' has been replaced. You can see the red pump just to the left and the value header (as I call it) a little above that. As mentioned the pump hasn't been checked because it 'kicks in' when we put the timer on Hot Water. The two way valve (I think) simple switches over to the hot water - everything's ok. But press the CH and when the valve switches to the CH : pop go the electrics
Attachments
You have a fully pumped Y plan system and the value header is the three port valve actuator head. Is this what was replaced ?
Yes, that's the one - actuator head, that switches from the hot water or central heating or can "sit in the middle" to get both. Sorry, I've had so much 'jargon' chucked at me I'm really confused haha.. my own fault for trying to be a helpful tenant
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