"topswage" wrote in message
. ..
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?

I don't see any reason why a digital electronic electric heat thermostat
wouldn't work. You have to be certain to get one for single pole, and one
that doesn't require a neutral. They're available, I've installed them.
There is another way you can go, which is how typical systems like yours are
wired. You need a switching relay like Honeywell R845, they cost about $50.
The 120 volts that's currently feeding the circulator and being broken by
the line voltage stat, would power the relay. The cable going to the
circulator gets connected to the switched load of the relay, and you can
either run thermostat wire from the TT terminals of the relay to any series
80 (standard 24volt thermostat) that you like, or even use the existing line
voltage cable for your thermostat wire