under cabinet heaters with relay and thermostat


Old 11-03-19, 05:29 AM
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under cabinet heaters with relay and thermostat

I have 3 heaters hooked up to an aube RC840t-240 relay and a honeywell thermostat. this setup has worked for years. last year the relay popped and stayed open so the heaters never turned off. replacing the relay fixed the issue and the relay itself was expanded and you could easily see something was wrong.

lately the thermostat has started blinking on and off and the heaters stay off and the relay never lights up. at first i thought it was the relay going bad again because i plugged the thermostat into a transformer that an electrician has to test thermostats and it lights up and appears to work fine. however after replacing the relay again it seemed to be working for about a half hour because the thermostat was lit up and i turned the heat up and all the heaters we going fine. but now the thermostat is once again blinking or staying unlit and the relay and heaters are off again.

im looking for any advice as to what to check next or a way to just force the relay on to get the heaters going while i wait to find a real electrician to come and check things out.

any help would be greatly appreciated.
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Old 11-03-19, 05:34 AM
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What kind of heaters are these? Space heaters? Water heaters?

Are all three heaters connected to a single thermostat/relay? What is the wattage of each heater or total wattage?
Old 11-03-19, 05:43 AM
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the heaters themselves are qmark QTS1504T toe space heaters. all three heaters are connected to the same relay with a single thermostat. the internal thermostats of the heaters themselves are bypassed.
Old 11-03-19, 05:49 AM
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Silly question, but does the thermostat have a battery? Some thermostats I've found as the batteries die, they get quirky. Even though it's connected to a transformer and possibly a C-wire, it may still be running off battery in some way.

Next question, what wires do you have going to your thermostat? R/RH? R/RH/C?

Temporarily, you can disconnect all the wires from your thermostat and wire-nut R and RH together. This is a good way to test just the relay. The relay should kick on and the heaters will go on until you turn them off (so don't forget about them or else you'll come home to a 90 degree house).

Presuming this R-RH test works, that will prove the relay is working reliably (or not) and narrow down the troubleshooting.
Old 11-03-19, 05:56 AM
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i do not see a battery inside the thermostat. itís a pb112-024t thermostat. and the wires on the back are labeled c, w, and r. sorry for saying honeywell earlier, i thought thatís what it was but it is also an aube.

black/green/red going back to the relay.
Old 11-03-19, 07:18 AM
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wire nutting the non-c together and turning the breaker back on didnít do anything. so even with a brand new relay in place that didnít work.

so now iím down to wondering a few things, and forgive me but my electrical knowledge is basic at best.

is it possible for the breaker itself to be bad?
could the wire from the relay to the thermostat be bad? nothing looks wrong on the two ends of the wire but no idea if anything may have happened on between.

i guess to verify the wire issue i could use a different wire to connect the r and rh of the relay itself

anyone have any other thoughts?
Old 11-03-19, 10:20 AM
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could the wire from the relay to the thermostat be bad?

I'd look into the transformer first, where is it? You said the thermostat appeared to be fine when connected to a test transformer so I would definitely check out the transformer that powers this control circuit first.
Old 11-03-19, 10:26 AM
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the test transformer was just a box that plugs into an outlet then has two wires coming off of it to plug a thermostat into to see if it powers up. an electrician built it.

the real setup is a breaker that goes to power the heaters with the relay and thermostat off of that.
Old 11-03-19, 10:33 AM
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He's using a self contained transformer/relay package.... RC840T-240.
It supplies a very limited amount of 24v to run the thermostat.
If shorting R to W doesn't operate the relay..... the module has a problem.

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