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

Reaction score
5
Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

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

-
Mentor
Esteemed
Arms
Reaction score
14,904
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

-
Esteemed
Arms
Reaction score
4,521
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

-
Mentor
Esteemed
Arms
Reaction score
5,288
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
Reaction score
5
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
Reaction score
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

-
Esteemed
Arms
Reaction score
1,960
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

-
Mentor
Esteemed
Arms
Reaction score
14,904
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.
 

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

Similar Threads

I recently wired a heating system with a UFH8 manifold and an unvented cylinder.... easy. Well it threw up a few problems. Initially I had the...
Replies
3
Views
564
A combi is heating 5 ufh zones downstairs and 1 radiator zone upstairs. It has a two port valve for each. My question is, would you fit this with...
Replies
4
Views
337
Hello I have a central heating system, with a Y plan layout. The neon indicator on the thermostat seems to be sometimes dimly lit / flickering...
Replies
1
Views
216
What can do this to an actuator? Overvoltage? Wear and tear? Stuck pin on the valve? This is in the German built kit house I’ve done work in...
Replies
3
Views
239
Hello Guys, I was wondering if any of you nice chaps could lend me some advice. So I have an open vented heating system with a 3 port valve...
Replies
7
Views
458

New Posts (Please Reply)

This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Top