It’s quite easy to use a domestic thermostat to control the furnace, when we suffered from a problem that wouldn’t allow our CCC2 to see the zone with our furnace (water in RJ11), I used a simple room thermostat with isolated contacts to turn the furnace on. The furnace is switched on by simply connecting the 2 blue wires that run from the A/C unit PCB together, this is easily accomplished at the furnace end.