Underfloor Heating Wiring

[dk1uk]

Hi – the previous owners installed electric underfloor heating in the bathroom, but annoyingly it will only power-up when the central heating is actually on.

In the cupboard downstairs is a junction box. There's a mains feed cable from the consumer unit. And a cable to the CH/HW controller and a cable to the boiler. The underfloor heating (UFH) feed is also run from this junction box. It seems odd to me that you'd configure the UFH to work this way, because not even the underfloor heating's programmer unit is powered unless the boiler is on – this obviously means that as soon as the boiler shuts off, so does the UFH programmer and so it resets the time etc. This configuration only works if you're happy to manually turn on the UFH each time you have a shower (and assuming the boiler is running at the time).

I want to be able to programme the UFH to come on the morning and evening regardless of whether the boiler is on.

The cables in the junction box are configured as follows:

- Mains feed: 3 core (live is connected to boiler live and CH/HW controller live)
- UFH cable: 3 core
- Bolier cable: 4 core (live is connected to mains feed live and CH/HW controller live). However, the black wire in the 4-core boiler cable is connected to another single core cable (it's actually a 3-core that someone has clipped to make a single core) - I can't trace this cable, it disappears into a corner of the wall. The point however, is that UFH live wire is also connected to this single-core instead of the mains feed live – is this single core cable a switch live?

My question is whether I can just connect the UFH live to the mains feed live in order to get around this issue where the UFH only works when the boiler is powered up.

I hope the above makes sense – would appreciate any advice.

Thanks

 

[PrenticeBoyofDerry]

I assume you have a wet system, which requires the boiler to heat the water that runs through your UFH pipes.
So without the boiler you are stuffed!

 

[dk1uk]

Thanks for the reply - no, it's the electric mat type under ceramic floor tiles.

Thanks

 

[SimonH2]

Need more details ...
Wet or electric system ? Does the rest of the CH have zone valves (S Plan) ? Does the layout of the plumbing allow the UFH to be serviced by the boilers without the rest of the CH being on ?
If in doubt - post pics o the various bits.

Depending on the answers, it could be a simple wiring alteration, or it could involve (potentially significant) plumbing alterations.

 

[riveralt]

I assume you have a wet system, which requires the boiler to heat the water that runs through your UFH pipes.
So without the boiler you are stuffed!

I thought the OP said

the previous owners installed electric underfloor heating in the bathroom.

 

[dk1uk]

Hi - it's definitely the electric type (not a wet system).

Thanks

 

[PrenticeBoyofDerry]

Hi - it's definitely the electric type (not a wet system).

If that is the case, sorry heads not screwed on.
You would require to disconnect the part of the circuit from boiler to UFH.
It would be possible to have the UFH on dedicated circuit and a control unit.

Do you have the brand make of system and do you know what output the mats have?

 

[ban-all-sheds]

I would remove all the cable between CU-Boiler

I hope you wouldn't.

AFAICT, the OP wants to get his UFH to work without the boiler needing to be on, not to stop the boiler from working.

 

[dk1uk]

Many thanks. Trouble is that I don't feel confident touching the CU.

Could I take effectively take a spur off the existing boiler mains feed cable instead? What I mean by this is cutting the mains feed cable, reconnect it with a choc block and then connect the UFH to that. Or am I just making problems for myself taking that approach?

Many thanks

 

[riveralt]

Many thanks. Trouble is that I don't feel confident touching the CU.

Perhaps then you should get an electrician in to help you sort out this problem. It isn't necessary a big job but....

Could I take effectively take a spur off the existing boiler mains feed cable instead? What I mean by this is cutting the mains feed cable, reconnect it with a choc block and then connect the UFH to that. Or am I just making problems for myself taking that approach?

From the way you describe the operation of the UFH I would suspect that the wiring is bit more complicated than simply breaking into the main cable.
As SimonH2 said we need more information on how the links between the boiler and the UFH have been made - for that you either need to provide photographs of the inside of the junction box with pointers to the cables identity or as I said get someone in to do it for you.

 

[dk1uk]

Thanks riveralt - agreed if may be a bit more than I'm capable of. Inside the junction box there are some cables that I can't trace - perhaps for thermostats. Rather than risk screwing it up, I'll get someone qualified in.

Thanks again.

 

[knowall]

Call an electrician

 

[ban-all-sheds]

You can kind of see the logic in deciding that when the programmer called for heat would be the time to fire up the UFH.

Were it not for the outrageous dynamic lag of UFH, and the fact that the UFH programmer will get screwed up.

 

[OwainDIYer]

I'm rather surprised that electric underfloor heating (which in even a small room can be well over 1 kW) would be powered off a heating control circuit which would usually be a fused spur at 3A or a dedicated circuit at < 6A.

Disconnecting the UFH from the boiler wiring entirely and rewiring it to an appropriate power circuit would probably be advisable.

 

[ericmark]

I'm rather surprised that electric underfloor heating (which in even a small room can be well over 1 kW) would be powered off a heating control circuit which would usually be a fused spur at 3A or a dedicated circuit at < 6A.

Disconnecting the UFH from the boiler wiring entirely and rewiring it to an appropriate power circuit would probably be advisable.

I would agree with you but wonder why done that way in the first place? I have a feeling something has been missed out somewhere.

Normally in a bathroom special underfloor heating is used with a earth surrounding the element in some way either as part of the heating cable or a mat above the heating cable and always protected by a RCD.

It will also normally have a pocket with a sensor in which measures the temperature of the floor and a thermostat which also measures room temperature but the latter often has to be outside the room because it is a bathroom which does present some control problems.

In the one I fitted the thermostat fitted in a round conduit box which was deep so it was right against a tile in the bathroom how others measure the temperature in the bathroom I don't know.

The Heath Robinson set up may be because the thermostat is not measuring the floor or room temperature as it should, and to simply move the supply could cause some over heating.

The one I fitted was a failure as it failed to get the room warm enough and the thermostat sensor in the pocket failed and broke where I tried to remove from the pocket so now controlled only by room temperature. The tiles are just cool enough to walk on yet do not heat the room enough without also having towel rail running and to be frank the towel rail is enough on it's own.

The under floor heating was fitted to dry out the floor so my mother would not slip on it but once cooled by the shower it takes 1/2 an hour to reheat and dry the floor by which time she has left the room anyway.

It is as a result not used.

So with that in mind I wonder if some thing missing or failed with the system in question or if fitted by some DIY guy does it comply with the safety requirements for all we know could be laid direct on floor boards and the wiring was done to stop it running for too long and burning the floor boards.

For me alarm bells are ringing and I would advise you get it checked by some one who knows what they are doing before doing any alterations to wiring. In fact before using it again.