I'm attempting to replace an old thermostat with a Honeywell LinevoltPRO 800 programmable thermostat. The heat is supplied by ceiling panels and works fine. The present unit is wired in series with another thermostat in an adjacent room and when I successfully installed the unit last spring, the downstream thermostat failed to work. (heat in the controlled area worked fine) The existing thermostat has a blue and a black wire feeding it. Each wire has 2 black wires wire nutted to it. The box also contains 4 red wires which are all wire nutted together. The 2 wires attached to the black wire are hot and one one of the 2 wires connected to the blue wire is hot. The Honeywell has 2 red and 2 black wires feeding it. Hopefully the answer is obvious to someone.:o

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Originally Posted by LUDDITE2006

I'm attempting to replace an old thermostat with a Honeywell LinevoltPRO 800 programmable thermostat. The heat is supplied by ceiling panels and works fine. The present unit is wired in series with another thermostat in an adjacent room and when I successfully installed the unit last spring, the downstream thermostat failed to work. (heat in the controlled area worked fine) The existing thermostat has a blue and a black wire feeding it. Each wire has 2 black wires wire nutted to it. The box also contains 4 red wires which are all wire nutted together. The 2 wires attached to the black wire are hot and one one of the 2 wires connected to the blue wire is hot. The Honeywell has 2 red and 2 black wires feeding it. Hopefully the answer is obvious to someone.:o

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The model number is TL8130A1005