Help with baseboard heater thermostat/relay

Thread Starter

jlggomez

Joined Oct 27, 2020
7
Hello, newbie here and thank you all very much in advance.

I have two 8’ electric baseboard heaters in my living room. Both are on the same breaker and both are controlled by one old Honeywell T87F low voltage thermostat and a White-Rogers relay box in the basement. One of the heaters will not turn off even when the temp is lowered all the way on the thermostat. The other heater operates normally. Logic (?) tells me that the problem has to be the relay and not the thermostat. Am I on the right track in trouble shooting this? Any thoughts and/or suggestions would be very appreciated. Thanks a lot.
 

drc_567

Joined Dec 29, 2008
924
... The point contacts, on the problem relay, may be sticking. One diagnostic trick is to find a suitable object, such as the hand!e of a screwdriver, and tap, with reasonable vigor, on the relay casing. Another option, if the problem relay is inserted in a socket, is to remove it and examine the points for corrosion or oxidation of any sort. At one time, very thin, miniature files were sold to enable cleaning of the contact point surfaces.
 

drc_567

Joined Dec 29, 2008
924
Thank you for your reply. No, the relay is not inserted into a socket. Would spray contact cleaner be of any help?
... Are you able to remove the relay cover case? If so, then try using electric contact cleaner spray on the point contacts. Do not use ordinary silicone spray, since that would not help.
 

Thread Starter

jlggomez

Joined Oct 27, 2020
7
Thank you all for your responses.

gramps, you may well be correct. However, I did go in there and sprayed Deoxit on all of the two relays’ electrical contact points. One in particular showed some corrosion which seemed to be making the gap between two contact points very very narrow compared to the other relay. I used a thin file to scrape the corrosion off along with Deoxit. Well, what do you know?! It has been working fine for a few days. Hope it stays that way.

Thanks again.
 

sagor

Joined Mar 10, 2019
284
Using a file to scrape off the corrosion probably destroyed what remains of a "good contact". While the relay may work for a while, it will fail soon, probably with a stuck (welded) contact. The relay is finished. Time to shop around for a replacement relay.
 

Thread Starter

jlggomez

Joined Oct 27, 2020
7
Sagor, thank you for your response. I don’t at all doubt what you describe, but please clarify; always trying to learn about these things. As you probably know, so apology if I am stating the obvious, the “contact point“ I refer to is a flat metallic flange (?) that touches (or not) the end of a small upward pointing metal bolt. My reasoning was that since corrosion can cause a build up of material it may have narrowed, perhaps even closed the gap, in effect causing the very thing you describe. I was very gentle with the file and I doubt (hope?) that I scored the surface of the flange. How exactly, and for what reason, would removing corrosion destroy a good contact unless corrosion builds up again? Are you suggesting that there is some other problem besides the corrosion that keeps the relay from working properly? As I mentioned previously the gap between those two points is noticeably wider on the other relay. Can that gap narrow or widen over time for some reason?

Thanks again for your thoughts.
 

crutschow

Joined Mar 14, 2008
25,680
The "corrosion" is likely melted contact material due to normal arcing when the relay contacts open.
Depending upon the contact material, using a file to clean the contacts may or may not give you a good extended life for them.

If you just want to wait and see if they fail again, that would be okay.
If you don't, then you should replace the relay (or probably both since the other relay contacts are likely also similarly burned, although it hasn't yet failed)..

For longer life you might consider replacing them with solid-state relays of the appropriate rating.
What is the voltage and type (AC or DC) going to the thermostat and driving the relay coils?
 
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Thread Starter

jlggomez

Joined Oct 27, 2020
7
Crutschow, thank you for your comprehensive response. I am in the USA. The two 8’ electric baseboard heaters run off one double pole breaker (240V AC). The thermostat is a Honeywell low voltage type (24v).

Thanks again.
 
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