We have 2 electric baseboard heaters in the same room that are wired to a Cadet mechanical thermostat. One heater seems to stay on continuously even with the thermostat turned off, while the other is cold. I have felt the thermontats several times and they are always the same. I tried different settings as well. They remain the same.
Lots of possibility’s here, bad thermostat, bad heater . But more information is needed. Are these 120 or 240v heaters? Is the thermostat single pole or double pole (2 connections or 4) ? I have seen where a single double pole thermostat is controlling 2 heaters on both 120v and 240v , I have also seen 1 welded contact set and 1 burned open, so it could be the thermostat. Turning off the breaker before working on this and note if it is a single or a double (1 wide or 2 wide) pull the thermostat out and let us know how many connections. I am guessing there will be 4 but it could be 2. Last we would need to know the nameplate rating of the thermostat, and the heaters.
Since this probably worked in the past Without any test equipment I would replace the thermostat, if you pull it out and find 4 wires connected this is the most likely cause of the problem.
If you only find 2 wires connected to the thermostat it may have welded the contacts and 1 heater failed , then we will need all the requested information and a photo of the wiring in the thermostat box to provide you with a safe path forward.
When changing thermostats keep track of the wires this is important a double pole thermostat can control 2 double pole heaters (240v) and you don’t want to get the wires mixed up. The same is true with single pole heaters (120v). You want to keep the wires on the same circuit if fed from 2 breakers , they should be handle tied but some older homes 2 120v circuits going to a single thermostat predates handle ties as in a multi wire branch circuit.
Let us know the additional info or if changing the thermostat worked.