I have a family member that is living in a 50s/60's small 4plex that has radiant ceiling heat. The heat no longer shuts off but stays on 24/7. I am not savvy with old electrical thermostats but my thinking is that might be the problem. The landlord is unresponsive to any issues they have and I wanted to do it myself as I have replaced thermostats in the past. Honestly, I am pretty clueless about electrical circuits and having replaced a few breakers, or adding a ceiling fan, that's about it. Short of paying for an electrician to diagnose the problem, how would you proceed if you were me and what kind of thermostat should I look for?

I would call an HVAC professional immediately after sending the landlord notification that this problem has existed for some time and he has been previously notified without response. And, tell the landlord the cost of the repair, if less than rent, will be done and deducted from next month's rent. If more than that? There must be some form of legal procedure or regulatory agency which could be threatened.

I assume the tenant pays for utilities. If not, open the windows and tell the landlord.

I've had both good and bad landlords. And I've done many minor fixes for them. For a good landlord I might consider replacing an old dumb thermostat with the same, after getting his permission. It is probably 3 wires and very simple. However, it does run risk of him claiming you somehow damaged his very expensive furnace which he will now want you to pay to replace.

So I personally would not make this repair.

All of the in the ceiling heat cable that I installed, back in the early '70s used line voltage thermostats that switched the 240 volt load to the ni-chrome wire that is embedded in the plastered ceiling. It most likely needs a new t-stat. Not a big deal.

I have good news for myself. I finally found a high voltage thermostat and that did the trick. I shouldn't be shocked at how clueless the folks are at Menards and Lowes when it comes to older technology. No one had any idea what a HV thermostat is and how it is different, but that is todays world. Oh, I could not buy one from the big box stores and found a local building supply that had two. Thanks for the advice and time to move on to another project.