Underfloor Heating


29 Jul 2008
Reaction score
United Kingdom
Had underfloor heating (electric) installed in our bathroom, downstairs concrete floor a fortnight ago.

Used matting and thermostathttp://www.screwfix.com/prods/39460...ng/Klima-FHT-Control-Digital-Room-Thermostat# from screwfix. Mat and control were fitted by builders not by me.

Turned the thermostat on last night and set up as per the manual, the temp sensor looks to be registering floor temp, date and time all ok, display reads 'heating' but the floor is cold.

No error messages showing but i have yet to resistance test the floor cable.
Any ideas could it just be user error?

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would i need to take the wires fully out of the thermostat to check resistance or can i leave connected up?
You need to fully disconnect them.

How long did you leave it switched on for?
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it has been on for a good few hours, still showing 12 deg for the floor temp though it shows that it is running 'comfort' program 24 deg. Floor is stone cold though.

will disconnect and check ohms, though i suspect the worst :cry:
hope it is just a dodgy thermostat.
How would I check the temp probe resistance?
readings (forgive the possibly idiocy of meter reading confusion)

sensor probe 20.6 ohms @ 200K
heating element 0.344 ohms @ 2k (pos / neg)
how would i check for earth continuity on the heater element?
That resistance reading sounds about right. I would say you have the comfort heating and heating settings the wrong way round. Try setting both for a higher amount (eg 40 degrees). Then you'll know whether it is working. Give it plenty of time to warm up.
Turn your meter onto AC volts and see if there is 230V across the input to the controller.
Then check and see if there is 230V output to the floor element.

If no output then the controller is probably faulty.
on taking the thermostat off the wall to ge at the wires it was obvious what the problem was. THe builder had wired the input of the heater element to the input on the therm but had wired the output to the live of the power supply. swapped the wires over and we have heat.

He cannot have even tested it as working then. This throws up some serious concerns:

Was the mat installed by a registered electrician?
Does it have an RCD fitted?
Do the other circuits (ie the lights) have an RCD fitted?
Did the builder give you an Electrical installation Certificate for the work done?
Did he notify the works to the local authority in compliance with building regulations Part P and have you had a Certificate of Completion?
(like this)

He must do all of those things.

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