RCD keeps tripping

[rotadays]

Hello,
RCD is tripping when I move the room stat to (call for heat).
Conventional boiler, Mega Flow system, was having intermittent fault with the motorised valve where the boiler wasn't flashing up to supply hot water, removed the MV a few weeks ago fitted a new one and wired it in only to find the clutch/return spring was broken so returned it and refitted the old one, opened and closed the main 2 port valve it is attached to with a touch of WD40 and pliers seemed to free it up, wired it up like for like as previously fitted, quite confident the wiring is ok as the hot water has been ok for weeks.

I have tried a few local H E but they are all snowed under with people having the same problem getting colder heating on problems. So I would like to try to fix this myself if possible.

I have looked at the Room stat no loose wires
No loose wires in the wiring box where I connected the motorised valve.
Which makes me wonder if it is the HW and CH controller situated under the boiler?
Could it be the Motorised Valve?
If someone could advise a logical system check a fairly competent DIYer could follow I would really appreciate it as the wife is getting cold at night and is looking fierce.

 

[gasmanstu72]

does it blow when you're on HW too?

 

[oldbuffer]

1. If its the RCD tripping it suggests you have a fault to earth.
2. If its an MCB tripping, more likely to be a live to neutral fault.
3. Power off. Room thermostat not calling. Turn to calling, test for neutral / earth and live / earth short circuit (test in wiring centre).
4. Room thermostat off. Turn to calling, test for neutral / live short circuit (test in wiring centre).

You need a multi-meter, not a "neon screwdriver".

Be aware that it is not uncommon for people to use the earth (circuit protective) conductor as a switched live. Its wrong and dangerous, but avoids using proper 4 or 5 core cable on occasions.

 

[rotadays]

does it blow when you're on HW too?

Thanks for replying appreciate that , it is fine with the HW supplies everything as it should

 

[rotadays]

Appreciate the replies, my electrical knowledge is very basic so I wouldnt feel competent to carry out those checks. Not sure about the forum rules are you allowed to offer your sefvices on here ? I live in Weston Super Mare

 

[gasmanstu72]

basics here, but if it works on HW you can discount components that work on both CH & HW like the boiler and pump, also the cylinder stat too. the programmer is switching on without issue and it's just when you turn the stat up?
change the room stat, they're not expensive and you'll probably get one that fits the same backplate as what you have saving you the need to alter the wiring, just remember to safely isolate the power first! it could well be more detailed fault but it might save you a few bob trying this first, if in doubt call a pro

 

[rotadays]

I was hoping it may be a faulty programmer I have the British Gas UP2 programmer , just found a second hand one on flee bay, if its a like for like replacement would it just be take the old one off the backpkate and push fit the new one ?
Actually just found a Drayton LP722 programmer screwfix looks like a straight swop will try that, hoping for an easy fix.

 

[rotadays]

basics here, but if it works on HW you can discount components that work on both CH & HW like the boiler and pump, also the cylinder stat too. the programmer is switching on without issue and it's just when you turn the stat up?
change the room stat, they're not expensive and you'll probably get one that fits the same backplate as what you have saving you the need to alter the wiring, just remember to safely isolate the power first! it could well be more detailed fault but it might save you a few bob trying this first, if in doubt call a pro

Thanks for that, I have just checked again, turned the programmer on to CH 'on' left it for 5 mins all ok, as soon as I turn the room stat for heat it trips the RCD. I will try a new room stat although I only replaced the old Hollywell one about 18 months ago.

 

[JohnD]

...as I turn the room stat for heat it trips the RCD. I will try a new room stat although I only replaced the old Hollywell one about 18 months ago.

please show us a photo of the wiring connections on this stat.

removed the MV a few weeks ago fitted a new one and wired it in only to find the clutch/return spring was broken so returned it and refitted the old one, opened and closed the main 2 port valve it is attached to with a touch of WD40 and pliers seemed to free it up, wired it up like for like as previously fitted, quite confident the wiring is ok as the hot water has been ok for weeks.

Also of the 3-port valve, especially if there is any sign of a water leak near it. Bearing in mind that, since you rewired it, you might not have used the heating

 

[rotadays]

please show us a photo of the wiring connections on this stat.



Also of the 3-port valve, especially if there is any sign of a water leak near it. Bearing in mind that, since you rewired it, you might not have used the heating

Cheers for the assistance, Hopefully pictures may clarify and I take your point, I haven't used the CH after re fitting the MV apart from yesterday when my wife tried to put the heating on tripped the RCD straight away, when I tried it 2 mins later CH worked and I bled out all the rads reached their op temp. Now every time it trips the RCD

 

[JohnD]

terminal 8 appears to have a taupe wire connected to earth.

I'm not a plumber and have seldom wired these centres so there may be something I can't spot.

 

[rotadays]

please show us a photo of the wiring connections on this stat.



Also of the 3-port valve, especially if there is any sign of a water leak near it. Bearing in mind that, since you rewired it, you might not have used the heating

Thanks for all your help appreciated. I have 2x two port motorised valves, the one I have had problems with preventing the boiler from firing up with demand for hot water, HW motorised valve and the other a myson with a white cover will be for the CH system I assume.
So could it be either MV fault which is causing this problem? I have a complete new HW MV ready to fit, would a MV short cause this problem?

 

[JohnD]

I'd suspect a wiring error rather than a faulty component.

RCD trips can also be caused by plumbing leaks getting onto electrical connections.

 

[bernardgreen]

If that green yellow goes to Earth and the other wire in terminal 8 is the Brown from the motorised valve then Switched Live from the motorised valve ( the brown wire ) is connected to Earth. If that is the case then it is no wonder the RCD is tripping when you call for heat, The valve opens and when it is fully open ithe micro switch operates and puts Live onto the Switched Live.

 

[rotadays]

View attachment 126751

If that green yellow goes to Earth and the other wire in terminal 8 is the Brown from the motorised valve then Switched Live from the motorised valve ( the brown wire ) is connected to Earth. If that is the case then it is no wonder the RCD is tripping when you call for heat, The valve opens and when it is fully open ithe micro switch operates and puts Live onto the Switched Live.

Thanks for getting back to me I understand what you are saying I must have made a mistake rewiring the MV, unfortunately I have no reference point to know where the earth wire in '8' would go I took a picture with my camera prior to removing the wires so I am baffled, you obviously can't tell me where it should go only that this is the most likely cause for the rcd tripping.