Boiler enable / room-stat wiring for ufh system

23 Oct 2007
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United Kingdom
I have a Vaillant ecotec system boiler with a 240v room stat wired via a Danfoss wiring centre to control my ufh system. I have done all the wiring but am stuck at the point of connecting the boiler enable / live / switched live connections from the boiler to the wiring centre. (I will do the work myself then have a qualified electrical engineer to check it for me prior to hime commissioning it - (the father in-law)). My questiion if anyone can help is;

There is a 'Live from boiler' terminal and a 'Switched live to boiler enable' terminal on the ufh wiring centre and two terminals marked 3 & 4 on the Vaillant boiler (which are currently linked with a wire) for the remote stat. Question is which wire goes to 3 and which goes to 4 please??? Thanks.
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3 is live out from the boiler and 4 is switched live back in.

Unless specified by the ufh specifically you only need to have the switched live back into 4 and ignore 3.
OK, thanks. The ufh wiring directions state that it needs 'live from boiler' and 'switched live to boiler enable' so as you say, I will try 3 for the former and 4 for the later. many thanks. Knowledge is a wonderful thing.

And another thing! There is a plug for a heating pump on the Vaillant. The ufh pump is wired from the wirng centre so I guess I dont need this plug until I plumb my rads into this boiler (which are currently on my combi - its a long story!) Is my assumption correct?? Tnx.
Ignore this pump plug.

The pump in the boiler will circulate to all your rads. The ufh pump is just for that and to mix the flow and return water to reduce the working temperature in the ufh part.

The boiler pump works for the ufh zone as well.
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The boiler is an open vent type 438 without a pump - sorry I didnt make that clear. So does my logic make sense ref. my rad connections later?
Thats different then, it is not an Ecotec Plus System boiler :eek:

Yes the pump must be connected to the pump plug on these as the boiler controls the pump and pump over run.

This needs to be connected and working for the ufh as well as the normal rad circuit.

These boilers need a fast flow otherwise you will get the F29 (I think it is)fault code where the boiler thinks there is no pump working.
Forgive me but does that mean that the ufh pump should be wired from the wiring centre AND the boiler pump plug - or should I disconnect the wiring to the pump from the ufh wiring centre?
Usually the ufh pump is wired from the ufh wiring center. The ufh should have its own zone valve that is opened by a call for heat from the controller. When this zone valve opens the 230V is then sent to the boiler switched live from the orange wire to fire up the boiler and heating system pump.

The only problem ufh systems I have come across are those where the wiring has not been understood from the outset.
Yes the ufh pump is wired via the wiring centre for the ufh system. So I'll leave the pump connections on the boiler for my rad circuit then. F23 & F24 relate to the pump output - what do you do if you get one of these faults that the pump output is too low and you're warm enough????
Make sure the pump is set to max speed and that you have an auto bypass fitted and set up correctly.

Yes F24 & F25 are the pump codes on these as they are a re-vamped ecomax pro with a new pcb fitted.

They still retain all the problems of the old ecomax pro though :cry:

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