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Sir Sparks
Sir Sparks, President/Owner/ Master Electrician
Category: Electrical
Satisfied Customers: 2532
Experience:  US State Certified & UK Electrical Contractor for all electrical fields/disciplines
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My electric underfloor heating has stopped working correctly.

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My electric underfloor heating has stopped working correctly. The thermostat shows the floor up to heat almost imediately. I have turnned the max floor heat potentiometer up to max and the fault persists. I have checked the mat resistance and it is at the as installed value and bang on theproduct spec.
I am assuming that the floor probe or the thermostat is not functioning.
How can I check the floor probe?
Hi, Could you tell me how many wires and what colours are connected to your thermostat? Also are you in the UK?
Customer: replied 7 years ago.


mat - live, common and earth

supply - live common and earth

probe - brown, white


Probe resistance is in excess of 17 Kohms

Floor cold

I do not know what probe you have but typically they are thermo-couples and should not be nearly as high a resistance as 17K ohms. They produce a very small voltage to operate so without expensive equipment there is no way you can test it. If you connect the live's and commons together for 30 minutes to one hour you will confirm if the mat is OK or not. After that I suspect the thermo-couple but cannot be sure. Is it easily exchangeable?

Edited by Sir Sparks on 1/10/2010 at 5:48 PM EST
Customer: replied 7 years ago.

Unfortunately the probe is burried in the tile cement and not in a tube and hence it canot be replaced as easily as it should be.

I was thinking of replacing the thermostat and sensor for £25 off of ebay and just tape the sensor to the floor to run a test and if that fixes the problem then I may have to take up a tile to replace the sensor.


I assume you answer means 'by-pass the thermostat

If you could find a suitable place where it doesn't show then I think two pot epoxy would make a permanent solution once you check it works with tape. You might need to compensate for lost physical connection somewhat, in other words instead of setting it at 23C you may need to set it to 30C. If you were to put an aluminum plate over the probe before taping(epoxying) the contact should be even better.Let's hope it is the thermostat though.
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