I replaced my old mercury thermostat with a ct87k and it will not turn on. I have tried several so they surely are not defective. Hooked my old one back up and the furnace works. only 2 wire supply on a floor furnace. Any ideas?

Some furnaces have power switches on the service doors. They won't work unless the doors are in place. Shorting together the R and W should start the furnace.

The two wires are hooked to the baseplate at the R terminal and the W terminal. there may be a switch somewhere on thermostat for electric or gas heat. make sure its in gas mode. make sure batteries are fresh and put in correctly in regards to polarity. make sure furnace is on when doing any settings with the thermostat. make sure themostat is set to "heat". make sure themostat is calling for heat (turn way up to be sure its doing that) . check the troubleshooting guide that came with the new thermostat.