Need help repairing space heater control board Honeywell (KaZ Inc. HZ-709)

Thread Starter

Petrushka

Joined Apr 18, 2020
2
Hello, I am trying to repair my space heater. Basically, my heater sometimes will still heat even if switched off, or when I set the thermostat to a certain temperature and the actual temperature and readout is higher than the setting, the heater will still stay on when it should go off. The only way to get it to trigger the relay to shut off the heater is to toggle the thermostat setting button. Thanks for any help in troubleshooting this.

It's a Honeywell (KaZ Inc. HZ-709) oil filled space heater. See images:

IMG_4625.pngIMG_4482_01.pngIMG_4480.JPG
 

Tonyr1084

Joined Sep 24, 2015
5,268
Sounds like a bad relay. Either it's contacts are pitted and don't make good contact, making the heater not come on when it should, but then when it does come on - the contacts may temporarily weld themselves together.
 

Thread Starter

Petrushka

Joined Apr 18, 2020
2
Thank you @Tonyr1084! The heater does come on when it should, it just doesn't turn off when it should. It will continue heating to temperatures above the thermostat setting until I toggle the thermostat adjustment button then the relay shuts off the heat. Sometimes, even when I turn off the whole heater, it will still continue to heat. So not sure if this is a relay issue?
 

Tonyr1084

Joined Sep 24, 2015
5,268
Two ways a relay will not cut out - first, if it continues to be powered even after it should have shut off. Second, if the contacts inside the relay weld themselves together.

On the first possibility - it may be a control issue. If the relay is not shutting off because something is continuing to power it then it's not the relay's fault. We don't know what kind of thermostatic control is on the unit, whether it's electronic or a bi-metallic strip. A Bi-Metallic strip is made of two dis-similar metals who's heat expansion coefficients are different. One strip expands more than the other, thus causing a bending to either make or break a contact. The contact is a mechanical point of electrical connection. If that contact welds together (sticks) until you make a gross adjustment then the problem is located right there. That's the cause of failure to shut off - or even failure to turn on, as a formerly welded contact can have heavy carbon buildup on it.

On the second possibility - assuming the relay is functioning normally - the electronic controls, the electronic temperature sensor and associated control electronics are not clearing (shutting off) when it should. That can be a much more complicated issue to find and resolve. For that we'd need a picture of the board, both sides, the model number if possible, and any schematics associated with the circuit board and wiring.
 

Tonyr1084

Joined Sep 24, 2015
5,268
I know you posted pictures but I don't see any kind of temperature sensor whatsoever. And I've been away from this thread for a couple weeks and didn't remember you did post pictures before. Can you give us a picture of all the electronics and wiring? It may take several pictures, that's OK.
 
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