I had to hire in an electrical engineer for 5 hours yesterday to trouble-shoot my solar heat collection system in conjunction with a gas fired backup which the blower was running continiously... my brother had replaced the TOP of a Honeywell CT87A base...and have 4 wires from the system. Consequently, the top piece doesn't use the green wire (Lookup Honeywell website-thermostats-ct87A! Look at page 8 of the schematics which lists which wires work on which model...) and made the gas run ANYTIME the house called for heat, even if the solar system had the heat available- resulting in a gas bill of $492 and an electrical bill of $495 last month!