Why is my underfloor heating not working? 6 possible problems

We investigate the common underfloor heating issues and advise on the best ways to fix them

Underfloor heating not working? When installed correctly, underfloor heating is a low-maintenance, energy-efficient solution that delivers an even spread of radiant warmth. High-quality systems are designed to be robust enough to withstand years of daily use – which is why it’s so frustrating when you splash out on underfloor heating and it stops working.

Most of the common problems with underfloor heating not working occur due to mistakes at the design and installation phase. That is why it’s vital to bring in an experienced professional to specify and fit your system. The heated cable or pipe sits either in the screed layer or under the floor surface, where there’s little that can go wrong or damage the system.

Causes of underfloor heating not working

Here, we investigate some of the most common causes of underfloor heating not working and explain how to resolve them.

1. Poor design & installation

bathroom with white metro tiles on wall, brass shower head over bath and potted plant

(Image credit: Future PLC/ Colin Poole)

'The vast majority of issues of underfloor heating not working are down to poor installation or shoddy commissioning,' says Matt Densham, sales director at Robbens Systems. The heat output your system needs to deliver depends on multiple factors, including the age of the property to how well insulated it is. Your heating engineer should carry out a home heat loss survey before specifying the system to ensure all these variables are accounted for.

'It’s crucial that UFH systems are fully designed and installed by professional companies,' adds Matt. When the system is installed, the warm water pipes or cables should be laid at neat, regular intervals. This will ensure that the heat is distributed evenly across the floor surface, rather than a patchy heat with hot or chilly spots. If the workmanship looks messy or uneven at the pipe/cable laying stage, it’s a red flag, and the job may need to be re-done.

2. Not enough insulation

To get maximum efficiency from your underfloor heating, installing the correct level of insulation in your floors is a must. Otherwise, a proportion of the warmth your system generates will travel downwards through the sub floor and be lost. This issue can occur with both wet and dry underfloor heating systems.

'Poor insulation requires higher heating temperatures, which will not provide a comfortable living environment,' says Tom Edmunds, general manager at Wunda. 'In a property with good insulation levels, low temperature and energy efficient underfloor systems will perform perfectly, giving maximum savings.'

If you’re installing UFH as part of a larger refurb or renovation, you could also look at upgrading the insulation in other areas (eg loft, walls etc) as well as switching out draughty old windows for thermally-efficient replacements.

3. Incorrect floor finish

blue living room with striped carpet and brown sofa

(Image credit: Future plc/Dan Duchars)

Another common pitfall when underfloor heating is not working is laying an unsuitable floor finish. 'While most materials are suitable for UFH, care must be taken to select the correct type of underlay for carpets,' says Matt from Robbens.

'Heat outputs can suffer drastically if an insulating type of carpet underlay is used.' Laying thick rugs across large areas of your room will also have a negative effect on the overall performance of the system. Read more advice on underfloor heating with carpet. Smooth, hard surfaces such as ceramic, porcelain or slate tiles typically provide the best thermal conductivity.

4. Incorrect UFH controls

Although an error in how the controls are set won’t damage your system, it will prevent your underfloor heating from delivering warmth effectively. 'Trying to control the system like an old-fashioned radiator central heating system (where the heating comes on for a couple of hours in the morning and a couple of hours in the evening) will end up with a patchy setup that doesn’t seem to work very well,' says Matt from Robbens.

Instead, running the system continuously will result in better performance and help with preventing underfloor heating not working. The temperature in each of the zones where UFH is installed should be regulated by its own individual thermostat. Once the floor surface is up to the correct temperature, its radiant heat will continue to warm the space throughout the day, without continuing to run the boiler. 'By only running the UFH for a few hours a day, it won’t have time to warm the floor up to enable the rooms to be heated,' adds Matt.

5. Problems with the screed

white kitchen with island, ceiling beams and tiled stone flooring

(Image credit: Future PLC/Colin Poole)

Unlike with electric underfloor heating, if you have underfloor heating not working from a water-based system and the sand and cement screed was laid without the pipes being properly pressurised, it’s possible that the screed may be obstructing the pipework. This means the warm water flowing though the pipes to heat the floor above will struggle to flow through. During the installation phase, make sure that the screed is left to cure and dry properly without the system being turned on. Cool water should be running through the pipes when this happens.

Issues with screed can be difficult to rectify once this layer and the floor finish above go down. If you engaged the services of a professional heating engineer for the installation, you should request that they come back to resolve the issue, which may mean that the screed needs to be re-laid entirely. Note that you won't get these issues with electric underfloor heating systems, like those at The Underfloor Heating Store.

6. Trapped air

white kitchen with island, grey cabinetry and tiled stone flooring

(Image credit: Future PLC)

This problem of underfloor heating not working occurs with water-based underfloor heating. If air gets caught in one of the underfloor conduits and gets stuck, it’ll have a knock-on effect on the rest of the system. Taking the correct steps during the installation phase can help to overcome the potential for this issue occurring.

Do not fill the pipes with water from the boiler filling loop, as this will push the flow of water through your pipes too quickly and trap air. When your system is filled, water should be flushed right through the network of pipes so you can see it flowing in through one end and out at the other.

Once the system is installed and your floor finish has been laid, bleeding the system to release some of the air and water that’s trapped can help to alleviate this issue. Your supplier can provide a detailed guide as to how this is carried out with your unique system.

Rebecca Foster

Rebecca Foster started her journalism career in Bangkok in 2013, where she worked on the in-house editorial team at a luxury homes magazine. Since then, Rebecca has contributed to numerous property and interiors titles in the UK and Southeast Asia. She re-located to London in 2015 to work at one of the country’s leading self-build and home renovation magazines. In 2017, she left her job to split her time between freelance journalism and teaching yoga.