Central Heating tripping RCD?

[Phil Russell]

I am not electrically qualified but think I have a fair understanding of the basics. This is a puzzle to us: Over the past 3 weeks our RCD that controls upstairs lighting, downstairs sockets and central heating controls has tripped 3 times. We had the impression it was tripping in early morning so put a timer on the downstairs socket circuit. It went again this morning and the timer stopped at 6am; just the time the central heating comes on. Vaillant boiler, Dafoss timer/controller. So it seems the ch is most likely the culprit. Before 6am the ch is totally 'off' on the control panel (hot water and the radiator heating) so the automatic switch on at 6am is the total system.  When this has happened I have reset the consumer unit at c 7am and there have been no problems. The system is also totally off in early afternoon and switches on again at 2pm. It has not tripped in the afternoon. I can see no leaks upstairs around the tank and pump/gate valves (?) in the airing cupboard.  I have read it could be caused by condensation in the flue/boiler and this may fit given the cold nights recently and, of course, condensation will have dried up for the afternoon. We have not had this problem in previous years.

I plan to contact our central heating company to ask them to investigate ... do you think my amateur diagnosis is fair or am I missing a trick somewhere?

Advise welcome please, with thanks

Cheers, Phil

 

[Sidney]

When was you boiler last serviced?

 

[Murdoch]

If you have any motorised valves that’s where I would start but don’t expect drips or water pouring out

 

[NozSpark]

Just to help confirm that it's your central heating, set your boiler to come on 1/2 an hour earlier and see what time it trips now

 

[Phil Russell]

Thank you for prompt replies. Boiler is serviced every year and has the next one in January under our ch contract .

Last spring we had a similar trip problem but during the day ..and we tracked it down to a ch issue (by switching everything else off / isolating circuits). The trip operated every time the ch was switched on at the consumer unit but there was maybe a minute delay. The ch engineer diagnosed a wiring fault (lack of insulation on one wire going to the pump motor) and re-did it. All has been well until now.

Over the years we have had several motorised valves fail but never had one trip the consumer unit; but then there is always a first time.

The 6am bit is puzzling .. condensation?  There is nothing else that comes on at that time.

Cheers, Phil

Just to help confirm that it's your central heating, set your boiler to come on 1/2 an hour earlier and see what time it trips now

Good point. Will do but it may take a week or so to trip again, or maybe tomorrow ...

Cheers, Phil

 

[Sharpend]

Where is the boiler located? 

 

[West Sussex Heating]

Uncertainty you're finding that your combi boiler retains tripping the RCD shift on your fuse board and tripping the electricity, it might be a signal of a fault or leak inside your boiler system. This switch is a security feature that breaks the flow of electricity when there's a current leak to earth.

Two faults I had recently on central heating that tripped RCD's

1. A dripping valve that triggered the RCD to trip, when things dried out all was fine. So when I inclined up it functioned fine, took a while to diagnose.

2. On another job, the neutral and cpc were reversed on the terminals inside the boiler.

 

[Evans Electric]

You did well and identified the CH  as the culprit I'd say.   

I think by Sharpend's  question , he,s wondering if theres a damp issue somewhere with the boiler controls ...which has dried out by the afternoon .  

Might pay to re-check that previous tripping issue with the insulation missing .    But could be anything really .

Must say its good to have a Heating guy on the Forum . 

 

[Sharpend]

You did well and identified the CH  as the culprit I'd say.   

I think by Sharpend's  question , he,s wondering if theres a damp issue somewhere with the boiler controls ...which has dried out by the afternoon .  

Might pay to re-check that previous tripping issue with the insulation missing .    But could be anything really .

Must say its good to have a Heating guy on the Forum . 

I'm wondering if boiler is in the garage? Damp or needs a frost stat fitting? 

 

[OnOff]

I had that with my mid position valve a while back. That and 2 two port valves. Look alright from the outside:





Inside all crudded up:

 

[Evans Electric]

Onoff ,  I'm looking at that tee in the pipework ...   I can only see the olive  on the tee section   .....   can't see a the back nut  !!!!      Flood action required  !!!    Don't panic !!!

 

[OnOff]

Onoff ,  I'm looking at that tee in the pipework ...   I can only see the olive  on the tee section   .....   can't see a the back nut  !!!!      Flood action required  !!!    Don't panic !!!

Mid repair!

 

[kerching]

'Y' valves! Work of the devil IMHBBO

Y bother!

just saying

 

[Phil Russell]

OK ... January 11 2021 UPDATE

Since my original post we have had our Central Heating people check out the system and found no faults. The electricians who work for the CH company came today and checked all the wiring around the 2 motorised valves and the pump and declared all was as it should be. They did not inspect wiring around the programmer.

So it is still a puzzle. Since my last post, the system has tripped a few times. On one occasion the RCD would not reset even when I switched the boiler off, which seems to eliminate the boiler. After an hour I tried to reset the system again and it reset OK. For the past two weeks we have heating and water set to come on and go off at different times. But it has not tripped in this time. Coincidence? 

But, a question please. If the valves are declared OK and we can eliminate the boiler as above, does that indicate the programmer as the most likely culprit? The programmer is a Danfoss one which I believe uses a common backplate. But I can get the same make and model from Screwfix for around £50. The call outs to our CH servicing people does cost a visit fee (less than normal for service contracts) but the call outs mount up and I am thinking a cheaper option is simply to get a new programmer and plugging it in.

Am I missing a trick or is my logic sound? What would you do, apart from putting on another jumper?

Cheers, Phil

 

[UNG]

OK ... January 11 2021 UPDATE

Since my original post we have had our Central Heating people check out the system and found no faults. The electricians who work for the CH company came today and checked all the wiring around the 2 motorised valves and the pump and declared all was as it should be. They did not inspect wiring around the programmer.

So it is still a puzzle. Since my last post, the system has tripped a few times. On one occasion the RCD would not reset even when I switched the boiler off, which seems to eliminate the boiler. After an hour I tried to reset the system again and it reset OK. For the past two weeks we have heating and water set to come on and go off at different times. But it has not tripped in this time. Coincidence? 

But, a question please. If the valves are declared OK and we can eliminate the boiler as above, does that indicate the programmer as the most likely culprit? The programmer is a Danfoss one which I believe uses a common backplate. But I can get the same make and model from Screwfix for around £50. The call outs to our CH servicing people does cost a visit fee (less than normal for service contracts) but the call outs mount up and I am thinking a cheaper option is simply to get a new programmer and plugging it in.

Am I missing a trick or is my logic sound? What would you do, apart from putting on another jumper?

Cheers, Phil

So has anybody checked the RCD tripping current with a ramp test and also checked if there is any leakage current from the circuit in question

 

[Murdoch]

So has anybody checked the RCD tripping current with a ramp test and also checked if there is any leakage current from the circuit in question

doesn’t sound like it

ive not yet seen a controller tripping an RCD, but I seen many “weeping” valves tripping rcds and judging by the rust on those valves .......

 

[SPECIAL LOCATION]

OK ... January 11 2021 UPDATE

Since my original post we have had our Central Heating people check out the system and found no faults. The electricians who work for the CH company came today and checked all the wiring around the 2 motorised valves and the pump and declared all was as it should be. They did not inspect wiring around the programmer.

So it is still a puzzle. Since my last post, the system has tripped a few times. On one occasion the RCD would not reset even when I switched the boiler off, which seems to eliminate the boiler. After an hour I tried to reset the system again and it reset OK. For the past two weeks we have heating and water set to come on and go off at different times. But it has not tripped in this time. Coincidence? 

But, a question please. If the valves are declared OK and we can eliminate the boiler as above, does that indicate the programmer as the most likely culprit? The programmer is a Danfoss one which I believe uses a common backplate. But I can get the same make and model from Screwfix for around £50. The call outs to our CH servicing people does cost a visit fee (less than normal for service contracts) but the call outs mount up and I am thinking a cheaper option is simply to get a new programmer and plugging it in.

Am I missing a trick or is my logic sound? What would you do, apart from putting on another jumper?

Cheers, Phil

RCD'S detect current leaking to earth.  Very, very very small amount of currents (30ma)..

As the majority of program controllers are of a plastic, (double insulated) construction, they do not require an electrical earth connection to work safely..

(although there is a normally an earth terminal to maintain earth continuity between the incoming and outgoing wires)

so I would doubt it is the controller...

and doing random swapping method of fault finding is never normally cost effective...

Unless the fault was on when your previous electricians & heating engineers did their tests, then I don't think they have actually proved much yet.?

so I don't think you can actually eliminate much from your investigations.

A very small internal leak on a seal in a valve or pump could easily allow a small drip of water to bridge a live component and metallic earth..

But also dry out due to the heat from the pipework leaving an intermittent fault..

Which would show as being all electrically good if not tested whilst the fault itself is on!

You could also be experiencing a cumulative leakage problem..

which is not 100% caused by the boiler.

Is the boiler on its own circuit?

how far away from the fuse box is it?

 

[OnOff]

Did they actually take the lid off the motorised valve(s) or just give a cursory glance? It's only one screw but do so with the power off.

 

[Phil Russell]

Thank you for the answers above. To update further, now that the problem is, we hope solved, this is the story. I don't know how I didn't cry or burst out laughing. Within an hour of the electricians' visit, the system tripped again and would not reset. Electricians were called and arrived Tuesday. . A new programmer was fitted (Time Guard TRT036 ... more about this later). System tripped. They proceeded to scratch heads and do more checks. Boiler electrics exposed and checked. Declared OK. Attention turned to the motorised valves, again. After much searching and testing and isolating the valves in turn, a short was found, live to earth, in one valve with evidence of water leaking inaround the motor. Why it was not found yesterday I am not sure. Attempts to remove valve head failed so plumbers were called. Plumber failed to shift valve head. It was clear to me that if water had got into the valve/motor (which was sited vertically) then the actual valve in the water pipe had failed and I suggested it might be best to replace the complete valve unit even if this meant draining the system down. But no ... continued to try and remove valve head. Electrician put force and leverage to shift it. It came adrift, breaking the water valve in the process and allowing a fountain of water across the bathroom. Electrician plugged hole with his thumb while I turned water off and the plumber set about draining the system down. A call to the plumber's base resulted in a new water valve and valve head being brought out, which was duly fitted.  So we are back up and running but in retrospect it may have been better to just drain down in comfort and replace the water valve once a water leak was detected. 

Now to the programmer. The electrician fitted a  TimeGuard TRT036. We expected a direct replacement for our old one (Danfoss) but were not asked what we wanted. He had to rewire the backplate though. The TRT is not easy to use and we are not impressed that the TRT036 is a discontinued model. It may also not have the functionality of our old Danfoss FP715Si. But at least it is working. If we cannot get on with the fiddly settings on the TRT036 we will get another unit fitted. Hopefully we would find a more user friendly replacement that is a direct plug in to the TRT036 backplate. From watching the electrician rewire the Danfoss back plate to the TRT one ... ... it does not appear difficult to put a new backplate up. Any comments on this?

So, all's well that ends well. We still have visions of the poor electrician sitting there for maybe 30 minutes with his thumb plugging the hole.

Cheers and thanks for all the comments, they have helped me understand what the electricians / plumbers were doing.

Cheers, Phil 

 

[roys]

Thanks for getting back to us, good that it is all sorted now.