Hi guys,

The heating system in my garage is on two circuits that both are using a contactor. One circuit has 4000w (two 2000w) electrical base boards heater connected to it, the other one has a 2000w convection heater. All this is controlled by a single digital thermostat (24V). Here is a picture of the electrical box and contactors:

http://i.imgur.com/v35GHjn.jpg



When I turn on breaker of circuit A (the 2000w convection heater) and circuit B is turned off, the convection heater is working as it should (being controlled by thermostat) and the other two base boards are obviously not working (breaker turned off).

When I turn on breaker of circuit B (the two 2000w base boards heater), both the two heaters on that circuit as well as the convection heater on circuit A are heating full blast ignoring the signal from the thermostat. It seems that as soon as circuit B breaker is turned on, everything is on all the time.

Circuit A original electrical base board was replaced by a convection heater few months ago and thermostat was switched to digital few months ago as well and it was all working fine for a while until this issue started more recently. The house is around 40 years old and this is probably the original heating setup.

Today, I've replaced the contactor on circuit B thinking that was the issue but it seems like the issue remains. I'm thinking of changing contactor of circuit A now but I'm having a hard time understand how circuit B can make circuit A turns on wrongly because of a bad contactor ? Or anything else for that matter ?

Note that I've also tried disconnecting the thermostat without any changes, problem seems to be coming from somewhere else.

If anybody has any idea what's going on or what I could look at, I would definitely appreciate your input

Thanks a lot!

 

I see what looks like two contactors, A and B, which is good.

What is not good is that it looks like both contactors have transformers on them. That's bad.
You can't have two self contained/powered contactors connected to a single thermostat.

 

Hi PJMax,

Thank you for your reply. What would be the side effect of running two transformers on a single thermostat ? I'm asking because it has been that way for ~40 years and it was working fine until now. You make me doubt and I went and checked the old contactor I replaced and it had a transformer on it as well so now I'm even more confused how it even ever worked

 

Two transformers connected together or to the same controller tend to run hot and usually end up frying one or both.

You need one powered contactor and one non power contactor. One transformer needs to control both contactors.

 

Interesting! Somehow that setup still was able to last 40 years but I guess I will have to look into replacing that whole setup. In the mean time, do you have any idea what would be causing my original problem (Both circuits stuck on when circuit B is turned on) ?

Thanks

 

You may have a fried relay coil holding the heat on. You may need to look into the relay to check its condition.