Hi y’all, as mentioned I have a Honeywell rth9585 that’s replacing a 10yr old thx9421. They look identical and the wiring seems pretty darn close. But after replacing the old Thermo the new one will not activate the furnace. A few notes
- old Thermo had an R and C connected.
- There is a third wire unused on both ends of the cable.
- the furnace was having intermittent issues that we thought was attributed to the thermostat and figured that’s a good place to start so we replaced it. Hence this post.
Only thing I can think of is there’s a missing third wire that this one requires and the old system did not. Or that there’s something wrong with the furnace, or wall mounted board.
Thoughts, ideas? I’d love to get this one working so I don’t have to hook the old one back up. Photo one: old vs new (box). 2 wires rc at the board, same two wires attached at the Thermo.
Gas furnace, 2 heat stages, one cooling. High efficiency and about 10 years old.
Thanks for the assist.
- old Thermo had an R and C connected.
- There is a third wire unused on both ends of the cable.
- the furnace was having intermittent issues that we thought was attributed to the thermostat and figured that’s a good place to start so we replaced it. Hence this post.
Only thing I can think of is there’s a missing third wire that this one requires and the old system did not. Or that there’s something wrong with the furnace, or wall mounted board.
Thoughts, ideas? I’d love to get this one working so I don’t have to hook the old one back up. Photo one: old vs new (box). 2 wires rc at the board, same two wires attached at the Thermo.
Gas furnace, 2 heat stages, one cooling. High efficiency and about 10 years old.
Thanks for the assist.
