How to test an electric underfloor heating system - Resistance and Insulation test

Electric underfloor heating system testing

One of the most important steps when installing an electric underfloor heating system is the testing. Once the final floor finish is laid it can be extremely frustrating to have to remove a section of the floor covering in order to fix an issue that would have been prevented by proper testing during installation.

A good installer will test the electric underfloor heating three times:

  1. As soon as it comes out of the box to make sure the heating cable is not damaged before installation starts.
  2. When the underfloor heating mat or cable has been laid. This test makes sure that no damage has been done to the cable while it was being installed.
  3. And a final test once the floor finish has been laid to make sure that no damage occurred during the installation of the flooring.

Once these tests are done the results should be recorded on the table in the instruction guide and handed to the homeowner. The homeowner can then use this information to register the warranty on our website.

Testing an electric underfloor heating cable is easy. All you need is a basic electric multi meter like this. We recommend using a meter that has clips at the end of the probes because it is easier to get an accurate resistance reading without having to hold the cables.

How to test the resistance of an electric underfloor heating cable:

How to test a electric underfloor heating system - resistance setup

The resistance of the cable is what make it heat up, so checking the resistance of the underfloor heating cable is very important and will ensure that your floor heats up as expected. This resistance test makes sure that the resistance value of the heating cable is the within the tolerance of the factory test results.

  1. Check the manufacturers resistance value stated on the underfloor heating label or the technical data table in the instruction guide.
  2. Switch your multi meter on and, if it does not set the range automatically, set it to read Ohms in the correct range.
  3. Usually, 200 ohms will be fine but if your mat or cable has a resistance value higher than 200 Ohms, select the next setting up on your multi meter which is normally 2000 (2K) Ohms.
  4. Connect one of the multi meter probes to the live (brown) wire and the other one to the neutral (blue) wire. Check the reading on the display and note it down on the table in the instruction guide.
  5. To pass the test, the reading must be within a tolerance of -5% to +10% of the manufacturer’s resistance value stated on the label. If your results are different give us a call on 0800 019 5899 and we can advise the best course of action.

How to test the insulation of an electric underfloor heating mat:

How to test an electric underfloor heating system - Resistance and Insulation test 1

This test makes sure that there are no breaks in the insulation of the heating elements by checking that there is no detectable resistance on the earth wire.

If there is any break in the insulation there will be a “leak to earth” which results in the RCD being tripped and your heating won’t switch on. Doing an insulation test will find this problem before it happens and give you a chance to rectify it.

To do an insulation resistance test with a multi meter follow these steps:

  1. Make sure your multi meter is set to the Ohms setting.
  2. Connect the live and neutral (brown and blue) wires to one of the multi meter probes.
  3. Connect the earth braid to the other meter probe.
  4. If the multi meter reads open circuit (OL/1/Infinity) that’s a pass! If you get a 0, it means the circuit is functioning and that is a fail. If your heating mat or cable fails this test it should be repaired by a professional or preferably replaced before continuing with the installation.

Electricians! How to test the insulation of an electric underfloor heating mat with an insulation tester

How to test an electric underfloor heating system - Resistance and Insulation test 2

Sometimes a break in the insulation can be so small that it cannot be detected until there is a voltage flowing through the underfloor heating wires. This can be the case if the underfloor heating passes both tests with a multi meter but trips the RCD as soon as the heating is switched on. To check for this issue you should isolate the underfloor heating form the electrical supply and test with an insulation tester.

To do an insulation resistance test with an insulation tester follow these steps:

  1. Make sure your insulation tester is set to the Ohms setting and 500V.
  2. Connect the live and neutral (brown and blue) wires to one of the multi meter probes.
  3. Connect the earth braid to the other meter probe.
  4. Press the TEST button or similar to energise the heating cable with a voltage and test the resistance.
  5. If the meter reads open circuit (OL/1/Infinity) that’s a pass! If you get a 0, a resistance reading the circuit is functioning and that is a fail and the heating mat or cable should be repaired by a professional or preferably replaced.

Get a free replacement for a damaged electric underfloor heating system

Members of our ThermoSphere Connect Installer Rewards Programme benefit from a limited number of free replacement underfloor heating cables/mats if the system is damaged during installation before the final floor finish is laid. Sound good?

Need a hand?

Our friendly and knowledgeable team are available from 07.00 – 17.00 Monday to Friday and you can contact us by phone, email, or use the instant chat on our website. All of our contact details can be found here or give us a call on 0800 019 5899.

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