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we have a conventional heating system and underfloor heating recently installed by the builders plumber - it’s all wired up (pump, valve, thermostat receiver etc..) but both the electrician and builder seem to be at odds with the connection at the boiler.

currently the boiler just has LNE and everything else is in the wiring box upstairs.

sparky has run a 5 core cable next to boiler and not been back to make final connections yet - currently sat in wago’s.

i’m after advice - should this cable be in the wiring centre or connected direct to the boiler. we have a stat for the ‘normal’ heating which is running fine, but i’m doing lots of reading and cant figue out how to wire this second stat - nor am i having any joy in getting it done by those ‘in the know’

any help appreciated. we have a baxi boiler with this connector block (see pic)

lne and l2 is whats scribbled on the cable in sharpie!


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Unfortunately, there are several ways it can be done correctly.
There will be a multi core cable between boiler and control center
Also one or multiple thermostats and time clocks.

All I would suggest is that before wiring up, the spark or the plumber should draw a wiring diagram after consulting the instructions for all the component parts.
Ensure that they can agree on the way forward when it’s down on paper before making any connections.

Moving a line on a sheet of paper is much quicker and cheaper than moving a cable in real life.


Hi - sorry to hear the folks on site are not finalising this for you, any ideas why? Surely the Builder is responsible to get it working, so no payment till resolved would be my first thought.

Can you further describe what’s already installed? How is the existing HW and CH configured? (2 two port valves in an S plan for example ...).

Here’s another thread that goes through some of the issues and might be an interesting read for you, but I think you’ll need on site help with this.
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thanks for replying. appreciate your time.

the builder is struggling to get someone in to do it and the original sparky has disappeared off the face of the earth.

the switch live (black...) i imagine would slot into the boiler block of CH plus... it becomes live when the thermostat is calling (underfloor heating...)

there is a junction box beneath the boiler with the LNE to the boiler - so I imagined that the 5 core would partly connect to that and the black would go inside the boiler block - but obviously i am unsure and dont want any issues.

i did call a gas man to look at it but he seemed confused by the wiring. this is an ongoing thing for us and kinda the last thing that needs doing.

any help appreciated.

s plan - 2 vlaves (one next to main water tank and one by the underfloor heating manifold with several cables going into the stat receiver.


Are you certain that there are only 3 conductors connecting into the boiler? This is unusual these days, but not impossible, and I think baxi do make a conventional boiler that can be wired this way.

If this is the case then the UFH cable will need to connect in to the wiring centre (joint box, or whatever else you may wish to call it) as the necessary terminals are not available at the boiler.

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