Underfloor heating RCD tripping

[boovee]

Hi. Before I call an expert out any thoughts on why my RCD has suddenly started tripping even when the power to the UFH on the thermostat is turned OFF? But trips sometime with heating on? If it's tripping with power off, could it be the thermostat, or a broken thermostat? The flooring has worked perfectly for a few months and only recently develop this fault.thanks

 

[endecotp]

Neutral-to-earth faults will cause RCD trips even when the device is off.

 

[boovee]

Neutral-to-earth faults will cause RCD trips even when the device is off.

Could this be on the non load side or load side or both?

 

[bernardgreen]

Why do you suspect the fault is in the UFH ? Is the UFH the only item supplied by the RCD that is tripping ?

 

[Taylortwocities]

When you say "off" do you mean off as controlled by the thermostat/controller or do you mean off when switched off at the fused connection unit

that completely isolates the UFH?

 

[boovee]

Why do you suspect the fault is in the UFH ? Is the UFH the only item supplied by the RCD that is tripping ?

Sorry, to be clear the RCD supplies the thermostat that then supplies the UFH.

 

[boovee]

When you say "off" do you mean off as controlled by the thermostat/controller or do you mean off when switched off at the fused connection unit

that completely isolates the UFH?

The power is only "off" on the thermostat controller (i.e. in a state where it is not supplying power to the UFH) and not by any isolation switch. And so, when the RCD trips, the whole thermostat is isolated. Thanks

 

[bernardgreen]

Sorry, to be clear the RCD supplies the thermostat that then supplies the UFH.

The power is only "off" on the thermostat controller

If nothing else is supplied by that RCD and the RCD trips when the thermostat is off then the fault is most probably a Neutral to Earth fault in the heating element or a fault in the thermostat / controller ( Earth to Live or Neutral )

And so, when the RCD trips, the whole thermostat is isolated. Thanks

which is what should happen.

To find the fault woll require the meausrement of the insulation resistance of the heating element, cabling and examination of the controller. ( insulation resistance testing uses 500 volts and this could damage the controller )

 

[pjcomp]

If it's tripping intermittently then finding it could be a pig. Has anything been nailed or screwed into the flooring recently which could have snagged the wire of the heating element? This might be triggered by someone wlaking on the floor and causing enough movement for the fatal contact to be made. Alternatively, it could be the RCD switch that's gone rogue. Does happen, though we sometimes forget that bit of the circuit.

 

[boovee]

If it's tripping intermittently then finding it could be a pig. Has anything been nailed or screwed into the flooring recently which could have snagged the wire of the heating element? This might be triggered by someone wlaking on the floor and causing enough movement for the fatal contact to be made. Alternatively, it could be the RCD switch that's gone rogue. Does happen, though we sometimes forget that bit of the circuit.

Thanks. It`s cheap enough to replace first so I will try that and then move on. I can do this, but anything else will require special equipment and testing. I know that all resistances were checked before, after installation including sensor probe and all were within tolerances. Nothing has been screwed in since to the flooring or surrounding area. Thanks for the advice so far...