i have a 2 wire set up for my very old thermastat, just bought a new one at rona.... one wire is black the other white... where do i install into the new unit.... i tried what the book says but the furnace will not turn on, put the old one back on and no problems

black white wire tells me that you have a 120, or 240v thermostat requirment. Are you sure you didnt buy a 24v themostat. have to make sure the new thermostat is compatable with your system.

What type of heat do you have? electric baseboard, forced air (gas or electric) , hot water(boiler).

Post brand and exact model number of old thermostat.
Post brand and exact model of new thermostat.