Single wire to boiler

[mike 15]

I've moved into a property which has underfloor heating with a combi boiler.

 

There is no "signal" feed from the heating manifold/controller to the boiler - so the boiler heating mode is just "on" all the time. The controller has the facility  to connect a switched 240v live feed output which would be connected to the "LR" switched live terminal in the boiler. This would then signal the boiler to fire up only when the controller is calling for heat.

 

So the question is what kind of wire should be used for this single feed. The manifold is some distance from the boiler and the wire could be run behind the studded wall.  Is it OK to use single core wire for example with red pvc covering. Or is there such a thing as single core wire with the additional outer sheathing that is normally used with 2 or 3 core wiring?

 

Any advice would be much appreciated 

[PeterW]

They should both be on the same circuit / spur from memory - @ProDave can you confirm...?

 

Is the boiler running all the time then ..??

[Temp]

+1

I think the boiler and UFH controller should all be powered from the same switched fused spur so perhaps check that first. This switch is usually located next to the boiler.

 

If ithe controller is not on the same circuit you may need to run a permanent live from the switch to the UFH controller so that it is and a switched live back to the boiler. You also need to avoid using a live from one circuit and a neutral from another as that can cause false RCD trips.

 

See what others say but it might be necessary to run three core and earth..

 

Permanent live to power the UFH controller

Neutral to power the UFH controller

Switched Live back to the boiler

Earth

 

Alternatively I'm sure there are wireless devices that will send the switched signal needed.

 

[ProDave]

Can you post a picture of the UFH manifold controller, if possible with the cover off and close up so we can read the terminals.

 

A lot of them have a "volt free" relay contact as the "call for heat" from the manifiold in which case you would use a 2 core cable to the boiler and it would not matter if they were on different circuits.

[mike 15]

Thanks for the responses.

 

The UFH controller switched fused spur is itself fed from the boiler switched fused spur.

 

I've attached the wiring diagram for the UFH system. 

 

The controller is 24v. The bit we are interested in is the pump module which is effectively just a relay. The module has 240v feed (again coming from the same circuit as the boiler and the controller). This feed is switched through to the pump and to a motorized valve. When the valve is fully open a switch is triggered which then provides 240v signal to the boiler. Fiendishly clever!

 

Anyway, it's that last bit of wiring that I was asking about - single line feed. What kind of cable to use?

 

 

[mike 15]

So to clarify what's happening at the moment:- 

 

There is no signal connection from the controller to the boiler.

 

The combi boiler has a bridge installed  between LS and LR

 

This means the boiler heat mode is on all the time. If no heat is being called for by the controller, the pipe valves are all closed and the hot water goes round the bypass loop and the thermostatic control in the boiler fires it up and shuts it down accordingly.

 

The single wire feed from the control system would go to LR in the boiler

[ProDave]

I can't read that drawing, even if I zoom in, it's too fuzzy to read.  Can you take a higher resolution picture.

 

Be VERY careful, that is a 24V UFH controller, you might need a relay to connect to the boiler if it does not already have a volt free contact output but I can't tell from that drawing.

 

Oh and rotate the camera so it posts the right way up, my neck was getting a crick trying to read it. (meant in the nicest possible way)

[mike 15]

sorry, I'll try the photo again

 

[mike 15]

[ProDave]

thanks that's a readable version.

 

Have you got that 2 port motorised valve shown in the diagram?

[Nickfromwales]

Is there a mix of UFH and radiators? Any other zone valve / heating zone(s) / controls involved? Just one household thermostat / Ctrlr?

 

To answer you actual question ( lol ) there will be a need for a live core and a CPC ( earth ) in the same cable minimum. Therefore you will need a 3-core flex, 1.0mm2 in size, PVC / PVC type. You will use the brown and the earth, the blue can be a redundant core. If you buy 2-core flex you won’t get an earth conductor, just blue and brown   The earth MUST be connected if it’s carrying 230v. You could use a smaller cable as you only need to be = or > the amp fuse rating in the fused spurs 3a or 5a should be in them max. 

[mike 15]

Thanks

 

I was trying to avoid unnecessary complication by describing the set up as per the diagram. In actual fact there are no radiators so there is no motorised valve. There are multiple room stats and pipe circuits all controlled from the manifold/controller.

 

So to run a feed to the boiler (orange in the diagram) the connection would be made straight from the pump module (grey in the diagram) giving the desired result.

 

Interesting comment about the earth wire. I can connect the earth both at the boiler and at the pump module no problem. But out of curiosity, isn't it the case that many room thermostats as an example which act as a 240v switch using 2 wire layout don't need to be earthed and don't actually have an earth terminal? So am I right in thinking that 2 core wire is used in these cases without an earth wire?

[ProDave]

You must be 100% SURE that the boiler AND the UFH manifold are indeed connected to the SAME circuit before you make that assumption.  Not only the same circuit, but possibly the same sub circuit.  i.e you may have a "heating" circuit from the consumer unit that feeds the boiler via one Fuses Connection unit and feeds the UFH manifold via another Fused connection Unit in a different place.  It would not be acceptable to link the grey to the boiler call for heat under that situation.

 

If you had the motorised valve you could connect the grey and orange to the boiler L and SL but you don't

 

Unless you can be more certain about how it is all wired, the only safe way I can advise at the moment is a relay with a 240V coil connected where the motirised valve brown and blue are shown, and the relays NO contact connected to the boiler L and SL.

[Nickfromwales]

6 hours ago, mike 15 said:

Thanks

 

I was trying to avoid unnecessary complication by describing the set up as per the diagram. In actual fact there are no radiators so there is no motorised valve. There are multiple room stats and pipe circuits all controlled from the manifold/controller.

 

So to run a feed to the boiler (orange in the diagram) the connection would be made straight from the pump module (grey in the diagram) giving the desired result.

 

Interesting comment about the earth wire. I can connect the earth both at the boiler and at the pump module no problem. But out of curiosity, isn't it the case that many room thermostats as an example which act as a 240v switch using 2 wire layout don't need to be earthed and don't actually have an earth terminal? So am I right in thinking that 2 core wire is used in these cases without an earth wire?

The whole picture is necessary to get a full set of ( correct ) replies  "Elaborate away".

Yes, just a cable from the grey to the LR and you're done. That's all 230v so all good.

I've never done anything less WRT earth and 230v in the same cable tbh, so someone drummed that into me somewhere! Almost every double insulated controls I've ever fitted ( and I've fitted countless number of every kind going ) have had an earth terminal for looping a continuous earth path through. That has not been connected to the equipment, but just a stray terminal set in a bit of plastic / whatever that is a junction to maintain earth continuity, should it be that a downstream bit of kit requires a reliable earth arriving at it.

 

 

 

[mike 15]

Thanks for the helpful responses - brilliant.

 

I can proceed with the wiring as above, although one last thought -  I am tempted by the idea of a wireless link from the pump module to the boiler. 

 

So the usual room stat devices won't suit. This part of the system is already in place with the room stats and the controller etc. Instead, it really just needs to function as a simple switch. The sender unit could be wired into the pump module with earth and neutral and the switched live (grey wire). When the pump module calls for heat through the grey wire this would trigger the sender unit to signal to the receiver unit which would be wired to the combi in the usual way.

 

Anyone know if such a sender/receiver device is available?

 

Mike