Electrical problem with under floor heating

IMG_1953-LargeWe were called to a large property in Jesmond to look at the underfloor heating which was proving unreliable. After a brief discussion with the customers and a look at the control of the underfloor circuits it appeared that the system had not been set up correctly when it was installed 5 years ago.

Calling for heat

When any system is switched on it must “Call for heat” from the boiler and this is done by switching the boiler on via the “Switched Live” connection. We found that the underfloor heating system had not been wired to the boiler so even though there was as “call for heat” from the wireless room stats the system would never start up because it wasn’t connected to the boiler.

Wiring remedy

Visio-Wiring diagramIt would seem to be a simple fix to run a wire from the underfloor heating controller to the  boiler’s wiring centre but that’s where the problems started. The wire was passed through a thick brick pillar and then behind some kitchen units until it reached the boiler cupboard. This was then wired into the boiler as per the wiring diagram below. You will notice that the Honeywell wiring centre and the Myson wiring centre are wired through separate fused spurs and that there are two routed back to the mains RCD. Unfortunately the RCD is designed to detect imbalance in an electrical system and as such would find a fault when one of the wiring centres was switched on. The RCD would trip the circuits after it detected the imbalance as if the current had gone through a person. The only remedy was to rewire the house’s circuits so that everything went through on cable and one fused spur. The diagram below shows how it was rewired.

Visio-Wiring diagram V2

We suspected that the reason why the link wasn’t made with the boiler in the first place was because of the RCD imbalance problem. The customers were delight to have full control of the heating for the first time.

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