Getting underfloor heating can be an incredible domestic upgrade. Especially during the winter months, having a toasty floor that doesn’t immediately suck the heat out of your feet can feel like a godsend, making slippers much less necessary.
Due to the fact that it works at a much lower temperature than radiators, it can be confusing trying to figure out if it’s actually on or not. If you’ve found yourself in such a predicament, then here’s how to work out if your underfloor heating is actually working or not.
First, know what “working” feels like
Underfloor heating (UFH) is very gentle compared to other kinds of heating. Instead of near-instantly hot radiators, you get an even, slow rise in temperature; from a cold start, give it 30-60 minutes to show life at the floor, and a few hours to lift the temperature of the room.
A cheap infrared thermometer helps: you’re looking for the floor surface to sit a few degrees above room temperature (often 20-28°C, depending on design and coverings), and for it to feel unmistakably warmer near pipe runs or cable paths.
Some quick checks
One idea is to set the thermostat several degrees above the current room temperature, and confirm the system is actually calling for heat. Make sure that preset heating schedules aren’t holding it in setback mode, and that any child lock features aren’t switched on.
If it’s a new install from somewhere like Able Plumbers, or it’s been off for summer, expect a slower first heat as the slab warms through (especially if it’s under concrete). Thick rugs or dense underlay can mask heat – pull one back and test straight on bare tile or engineered wood to be sure.
If you have a water UFH system
For water-powered UFH systems, go to the boiler. The flow pipe from the heat source should get warm first, then the return pipe should follow, usually a few degrees cooler. Many manifolds have clear flow meters; you should see the little floats rise or the indicator moving once the zone opens.
A subtle vibration from the circulation pump is a good sign; a stone-cold pump and pipes with a thermostat that’s currently on suggests that there’s some kind of a control issue.
Check the system pressure on your boiler (it should be about 1.0-1.5 bar cold). If it’s low, the boiler may refuse to run the loop. On mixed systems, the blending/mixing valve should be warm on both sides – most UFH runs at roughly 35-55°C flow; if it’s cold, the valve may be shut or the zone actuators aren’t opening.
If you have electric UFH
For electric UFH, confirm the controller has power, check that the RCD for that circuit hasn’t tripped, and the thermostat is in floor-sensor mode if that’s how it was set up. The floor should start to warm locally within 15 minutes or so.
If the thermostat shows a wildly wrong floor temperature (for example, 5°C in a lived-in room while it’s clearly closer 20°C), the sensor will probably be faulty or miswired.
Underfloor heating is great when it works, but can be a bit of a change for some people. Learn how your system is supposed to run, so that you can spot any issues early on and get them sorted out.