Hello:

Replacing a very, very old Honeywell thermostat with one of those new
digital ones.
Have a forced hot water system (no cooling).

It is a 2 wire system.

The wires coming up to the existing thermostat (a mechanical one with the
mercury vial on a coil spring type)
are not color coded.

Also, the screws where these wires connect to the old thermostat do Not have
any molded-in labeling
that I can see. May have worn off.

My question is:

Since these wires are "probably" coming from the secondary of a transformer,
and operate a relay,
can I safely assume, probably, that there is no polarity involved, and
either can be hooked to
either connector on the new thermostat that is for a 2 wire system ?

The only reason I can think of that this wouldn't be true is if this
transformer secondary might have
one leg grounded, but I doubt (but am not sure) that this is the case.

Any thoughts on ?

Thanks,
Bob