On Feb 29, 5:54*am, topswage wrote:
My home is heated with a gas fired hot water boiler. *The system is
presently controlled with a 1950's style bimetal thermostat. I'd love to
replace the thermostat with an electronic set-back unit, but have
discovered that the thermostat is directly controlling the hot water
circulating pump--there's 120volt current running through the
thermostat, enough to fry most electronic ones. *I see though that there
are electronic thermostats designed to control electric baseboard
heaters, and will control 120 volt circuits--can I use such a thermostat
to control my circulating pump?

Honeywell makes ( or made) a kit with a relay, etc. for converting
line voltage systems to work with 24 V thermostats. Installed a couple
of these in a shop some years ago, so I hope they are still available.
That would solve your problem very neatly. HTH

Joe