Thanks for your response TTC. It seems that the floor heats up okay one day and not the next. I'll just have to catch it to test when it isn't heating, as you suggested.
The thermostat/controller would be by far the easiest to replace, so I hope it's that rather than the floor sensor...
Hope someone can help with ideas on what has 'gone wrong' with my bathroom Devi undertile heating. This was installed about 5 years ago, and has worked fine all that time. A couple of weeks ago, the floor was cold, but the Devireg 550 controller was still on and showing all the correct info -...