There is no power on our Honeywell Chronotherm IV Plus thermostat. There is no battery to replace when I removed the unit from the base in the wall. Where is the problem? Would appreciate any help.

It sounds like a low voltage problem. Check the transformer output in the furnace. It should be 24 volts output. If it is then the problem might be with the wiring to the thermostat or the thermostat itself.