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Old 03-23-2020, 12:36 PM
Cecil McKenzie Cecil McKenzie is offline
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Join Date: Feb 2011
Location: Emporia, KS
Posts: 502
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In my experience mercury relays have always failed on. I have melted paperweights and multiple vases melted together as evidence. When i started using my small Denver unit I had a couple failures with the MDRs failing in the off position which surprised me . After I started my furnace this year it ran fine then failed in off position. I could tap the relay and it would work again but then fail again. I replaced it with a relay I bought 8 years ago. It was different from many I had used in that it had brass bars connecting the two sides of the coils top and bottom. The manufacturer said this was to make them synchronized.

i was pleased since it ran much quieter than the old one. About 5 days later i noticed the furnace was at 1972 F when it said it was holding at 1950F. I am pretty sure it had been higher and then become unstuck.

When I talked to Denver they said that they thought solid state relays always stick on. I talked to Brice recently because I knew he used solid state relays. He said he though his have failed sometimes in the on position and sometimes in the off. Denver suggested a fail safe of some type to keep furnace from over heating.

These considerations have prompted me to seek advice from this board.
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