Hello:
Have just started looking for a new heating thermostat for my gas, forced hot water system. Probably a Honeywell. Been many and many a year since I've looked at these.
Have no schematics avail. for any of them, hence my ignorance, in part.
I guess most of them are now with a backlighted digital display, and either programmable or non-programmable.
They all seem to require 3 wires, power from 24 V, BUT also a few batteries, surprisingly.
Questions:
a. Why the batteies ? Can't everything be derived from the 24 V easily ? If it's for memory backup, don't they use a memory that doesn't require constant battery power ?
The implication is that if your batteries run down, your heqting system stops. Not good. What actually do you think the batteries do ?
b. My system now is quite old. Only 2 wires going to a simple SPST mercury swith in the thermostat.
Will these new thermostats work on 2 wires ? I don't see how they can ? If so, how ?
Thanks, Bob