This is odd. So it sounds like the element never turns off no matter what you do with the thermostat? What if you switch it to cooling? This sounds like a bad relay. I’ve never worked on an electric heat air handler before. But I have to assume it would need a big relay to switch the heavy amperage load on and off. I would locate that and use a multimeter to see if it’s receiving activation voltage while it is enɡɑɡed. If not then you have a stuck coil. If it’s receiving activation voltage at all times then your trouble lies in the circuit board. Relays are easier to get than circuit boards. For a relay you just have to match the coil voltage and make sure it meets or exceeds the amperage handling. There is one other possibility, some relays stay enɡɑɡed and require a signal to disenɡɑɡe it as well as enɡɑɡe it. These kind of relays have two coils, and then an auxiliary low voltage relay which switches the voltage signal between enɡɑɡe and disenɡɑɡe. You should be able to recognize this readily because the coil with have two sets of small wires going to two coil packs in the middle of the large relay. Many electric heaters have more than 1 element too and split feeds like a 2 pole 60 and a 2 pole 30 or two 2 pole 60’s (the breakers feeding it) in this case you would likely have two relays being controlled by different wires. At any rate there should be a schematic diagram inside the case of the unit. Usually on the back of the main access cover. There will definitely be a circuit board with your thermostat wires going to it. Again you might have 1 or 2 large relay blocks where your big feeds from the panel go into one side of and the other side feeds your elements, while wires will tap off those feeds to power the low voltage transformer which powers your control circuitry. So start out (circuits off) by opening the unit and locating the high voltage relays (follow the big wire entering the unit). Test for continuity from input to output. If you have it, look at the low voltage activation coil and see if there is 4 small wires connecting to isolated terminals to indicate that it requires voltage to disenɡɑɡe. If that’s not the case you probably have a stuck coil, which you can probably disenɡɑɡe by pulling on any exposed parts of the plunger. (A relay will have a low voltage coil around a magnet on a plunger which has copper on the bottom, when it enɡɑɡes it completes the circuit across the two sets of contacts. If you determine that this is the issue, take a good picture of it for a reference, tag wires that aren’t obvious. Number your big wires in and out and tag your activation wires for polarity. Note any additional wires tapping power off the inputs and outputs. Maybe you can correct the trouble. A replacement relay will be 50-100 bucks. If the relay is disenɡɑɡed, (no continuity across the big wires) then the problem lies in the control circuitry and will take a bit more analysis. Good luck. At least you do have heat when you need it despite the inconvenience of manually turning it on and off. It’s not a good idea to leave it on when the fan is not running because it could damage components in the case....
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