Discuss Wet UFH Tripping RCD in the Electric Underfloor Heating Wiring area at ElectriciansForums.net

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Hi. I’ve recently had installed a manifold (including zone valve and pump) for the newly installed Wet UFH in my extension.

The system is split into three zones 1) Hot Water 2) Extension UFH 3) The rest of the house which is the original central heating system.

All work fine when switched on individually and the original hot water and original central heating works fine when switch on together. However, if the newly installed UFH system is switched on with either the original hot water or the original central heating, the consumer unit RCD trips.

The supply to the UFH valve and pump is spurred from a different ring main that the spur supplying the original hotwater zone valve and original central heating zone valve and I thought that might be an issue. However, I temporarily provided a supply to the UFH valve and pump from the same ring main as the hot water and central heating which made no difference as the RCD continued trip when the UFH was switched on with either the hot water or the central heating.

Any suggestions as to what the issue may be ?
 

davesparks

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The supply to the UFH valve and pump is spurred from a different ring main that the spur supplying the original hotwater zone valve and original central heating zone valve and I thought that might be an issue.

Have you ensured electrical seperation between the two circuits?
Does the switched live to the boiler from the UFH come from a volt-free output?
Or have you created a situation where the two control circuits are directly connected together via the boiler switched live?
 

brianmoooore

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There was a similar thread last week where I suggested parallel neutrals might be the problem. In that particular case, I think the problem turned out to be elsewhere, but, for this one, that's what I'm going to suggest. - the live current through the RCD is finding its way back through two neutrals, only one of which passes through that RCD.
 

snowhead

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What type of consumer unit set up is it?

Split i.e 2 Rcd's?
(If above are there any circuits NOT connected via an RCD?)
Mainswitch RCD?
Individual RCBOs for each circuit?

As previous post, it's a neutral issue.
When the temporary supply was used I suspect a neutral fom the "unused" source was still connected.
 
OP
M
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What type of consumer unit set up is it?

Split i.e 2 Rcd's?
(If above are there any circuits NOT connected via an RCD?)
Mainswitch RCD?
Individual RCBOs for each circuit?

As previous post, it's a neutral issue.
When the temporary supply was used I suspect a neutral fom the "unused" source was still connected.
Hi. Thanks for the response.

I have a typical split consumer unit. One half not protected by a RCD and the associated CBs supply lighting circuits and the door bell. The other half is protected by a RCD and the associated CBs supply four ring mains and individual supplies to kitchen appliances such as the cooker and oven.
The supplies for the original central heating system, hot water and new UFH manifold components are taken from the ring mains via fused spurs. I’ve checked to ensure that the neutrals on each ring main are segregated and tied into the neutral termination bar on the side associated with the RCD and all appears to be fine.

I didn’t do the installation, but my understanding is that the main changes made are:
1) The installation of the UFH manifold (including zone valve and pump)
2) Provision of a supply from one of the ring mains via a volt free heating controller contact to open the zone valve and energise the pump.
3) I think the boiler start signal which goes through the switch on the zone valve is also taken from the same supply (Not sure if this could be the source of the problem ?)

I had hoped it would be a quick fix, but I think it’s time to hand it back to the guys who did the installation.
 
OP
M
Reaction score
5
There was a similar thread last week where I suggested parallel neutrals might be the problem. In that particular case, I think the problem turned out to be elsewhere, but, for this one, that's what I'm going to suggest. - the live current through the RCD is finding its way back through two neutrals, only one of which passes through that RCD.
Hi. Thanks for the response.

I have a typical split consumer unit. One half not protected by a RCD and the associated CBs supply lighting circuits and the door bell. The other half is protected by a RCD and the associated CBs supply four ring mains and individual supplies to kitchen appliances such as the cooker and oven.
The supplies for the original central heating system, hot water and new UFH manifold components are taken from the ring mains via fused spurs. I’ve checked to ensure that the neutrals on each ring main are segregated and tied into the neutral termination bar on the side associated with the RCD and all appears to be fine.
 
OP
M
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5
Have you ensured electrical seperation between the two circuits?
Does the switched live to the boiler from the UFH come from a volt-free output?
Or have you created a situation where the two control circuits are directly connected together via the boiler switched live?
Thanks for the response.
I didn’t do the installation, but my understanding is that the main changes made are:
1) The installation of the UFH manifold (including zone valve and pump)
2) Provision of a supply from one of the ring mains via a volt free heating controller contact to open the zone valve and energise the pump.
3) I think the boiler start signal which goes through the switch on the zone valve is also taken from the same supply (Not sure if this could be the source of the problem ?)

I had hoped it would be a quick fix, but I think it’s time to hand it back to the guys who did the installation.
 
OP
M
Reaction score
5
Hi. I’ve recently had installed a manifold (including zone valve and pump) for the newly installed Wet UFH in my extension.

The system is split into three zones 1) Hot Water 2) Extension UFH 3) The rest of the house which is the original central heating system.

All work fine when switched on individually and the original hot water and original central heating works fine when switch on together. However, if the newly installed UFH system is switched on with either the original hot water or the original central heating, the consumer unit RCD trips.

The supply to the UFH valve and pump is spurred from a different ring main that the spur supplying the original hotwater zone valve and original central heating zone valve and I thought that might be an issue. However, I temporarily provided a supply to the UFH valve and pump from the same ring main as the hot water and central heating which made no difference as the RCD continued trip when the UFH was switched on with either the hot water or the central heating.

Any suggestions as to what the issue may be ?

UPDATE:
I’m so annoyed with myself (and the installer) for making the assumption that the supply for the HW/CH system was spurred from a ring main protected by the RCD. It’s not ! It’s fed from a CB on the left side of the board and not protected by the RCD. The installer picked up a supply for the UFH from a ring main which is protected by the RCD.

Needless to say when the switched live for the HW/CH and the switched live for the UFH come together there is an imbalance and the RCD trips !

All I needed to do was look at the labelling on the consumer unit and it would have been sussed ages ago ! 🤦🏻

Both circuits now protected by the RCD and issue resolved 👍🏻
 

mattg4321

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UPDATE:
I’m so annoyed with myself (and the installer) for making the assumption that the supply for the HW/CH system was spurred from a ring main protected by the RCD. It’s not ! It’s fed from a CB on the left side of the board and not protected by the RCD. The installer picked up a supply for the UFH from a ring main which is protected by the RCD.

Needless to say when the switched live for the HW/CH and the switched live for the UFH come together there is an imbalance and the RCD trips !

All I needed to do was look at the labelling on the consumer unit and it would have been sussed ages ago ! 🤦🏻

Both circuits now protected by the RCD and issue resolved 👍🏻
So they are still on separate circuits?

How will you safely isolate one of the circuits, when it is electrically connected to another that is still energised.

That is potentially very dangerous, and further will cause you problems when your consumer unit is eventually upgraded to RCBO’s/AFDD’s.

Unless I’ve misunderstood something, your installer is clueless.
 

davesparks

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Both circuits now protected by the RCD and issue resolved 👍🏻

That has not solved the issue, you still have an incredibly dangerous situation which could lead to serious injury or damage to your heating system.

It sounds like you still have two circuits connected together via your heating controls, all of the heating controls should ideally be fed via a single switched fuses spur so that there is only one fuse protecting the whole thing.
Currently you must have two fuses protecting the heating system.
 
OP
M
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So they are still on separate circuits?

How will you safely isolate one of the circuits, when it is electrically connected to another that is still energised.

That is potentially very dangerous, and further will cause you problems when your consumer unit is eventually upgraded to RCBO’s/AFDD’s.

Unless I’ve misunderstood something, your installer is clueless.
 
OP
M
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You didn’t miss understand. Apologies, I didn’t take the time to explain the solution properly. The original dedicated HW/CH supply has been moved across to the RCD side of the board and the UFH is now part of the same circuit. I really appreciate you following up on my vague post 😳
 
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OP
M
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That has not solved the issue, you still have an incredibly dangerous situation which could lead to serious injury or damage to your heating system.

It sounds like you still have two circuits connected together via your heating controls, all of the heating controls should ideally be fed via a single switched fuses spur so that there is only one fuse protecting the whole thing.
Currently you must have two fuses protecting the heating system.
Apologies, I didn’t take the time to explain properly. The original dedicated HW/CH supply has been moved across to the RCD side of the board and the UFH is now part of the same circuit. Thanks for following up though, Much appreciated.
 

davesparks

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Apologies, I didn’t take the time to explain properly. The original dedicated HW/CH supply has been moved across to the RCD side of the board and the UFH is now part of the same circuit. Thanks for following up though, Much appreciated.

So both the UFH and the rest of the heating controls are now fed via a single fuse?
Or are the UFH and the other controls now fed from two different connections to the same circuit?
 
OP
M
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So both the UFH and the rest of the heating controls are now fed via a single fuse?
Or are the UFH and the other controls now fed from two different connections to the same circuit?
The UFH and the rest of the heating controls are now fed via a single fuse. So a 6 Amp CB on the RCD side of the consumer unit to a switched fused spur (with 3amp fuse) which supplies the heating controller and all the components within the system including those on the underfloor heating manifold.
 

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