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I have two electric heaters on the same circuit. They are connected in parallel, or at least the wires all come in the same box where the thermostat is installed.

Previous setup: 1 heater had a built-in thermostat, it was wired to skip the thermostat (directly connected to the load wire), other heater was going through thermostat. Worked fine.

New setup: Got rid of the heater with a built-in thermostat. Both old heater (2000W) and new heater (1000W, without built-in thermostat) go through the same wall-mounted thermostat now (basically I switched the one black / load wire to go before the thermostat). The 2000W element heats up fine for like 15 mins, then stops. The command at the wall-mounted thermostat still shows it is heating (it didn't reach the target temperature). The 1000W element is still going strong, but the 2000W becomes cold to the touch. A few hours can pass and the 2000W one remains cold. If I fiddle with the thermostat (decrease and increase temp target again), the 2000W starts heating again and stops after 15 min.

Test setup: I disconnect the 1000W element, and leave only the 2000W plugged in the circuit. The 2000W element heats up just fine, and can keep heating for multiple hours without having this weird behavior I get when both of them are hooked.

The thermostat is graded for 4000W.

Any ideas what I could try next? Should I replace the thermostat?

EDIT:

Some pictures.

Wiring Wiring

2000W heater I don't have exact model name2000W heater I don't have exact model name

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  • Specify the make/model of each heater and the thermostat. Also, pics of the wiring would probably be very helpful. – FreeMan Dec 18 '20 at 22:29
  • Please provide make and model of heaters in question. – George Anderson Dec 18 '20 at 22:30
  • Heaters : 1000W is a uniwatt uhc1002wc, 2000W is a uberhaus can't find a specific model number I'll add pics – levesque Dec 18 '20 at 23:28
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I suspect a poor connection to the 2000W heater when both were connected, rather than anything related to the thermostat or the heater itself.

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  • I didn't change the connection itself, I merely unplugged the 1000W heater itself from the wall where it is located (i.e. without touching the connections behind the thermostat), so if it worked for the 2000W that way it must mean the connection is good? – levesque Dec 18 '20 at 23:35
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    I would still suggest remaking the connections, with care, very tightly. I think in some way the 1000W connection is causing the 2000W to disconnect after heating a bit, and when you play with the thermostat you're turning it off, so things cool & it reconnects. – Ecnerwal Dec 19 '20 at 0:00

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