replacing mercury 2 wire to digital thermostat

[minime]

Hi,
i am no expert with household electronics, farthest ive gone is installing a ceiling fan... anyhow, let me get to the point.

i recently purchased a home with has radiant hot water system, with a gas furnace. It has a "white rodgers" mercury thermostat. I believe it is a very low voltage system, because i have two small black wires which attached to the thermostat.
Now i went and purchased a two wire stat, thinking it would work. But the display goes , except no controlling, for example..i cranked the heat.left it for 10 minutes, and nothing happened.

what should i be purchasing ifi want digital controls ?

thank you..

[hvac4u]

on a 2 wire heat system, connect one wire to R and the other to W. you will HAVE to get a stat that runs off batteries. others need a third wire (common)

[minime]

is it possible to tap into common somwhere else in the system.
for example , i have two zones, two thermostats... each thermostat goes to what looks like a valve (last component before the hot water travels to the baseboards) which has 4 terminals on the back.
I if there is a common their, can i use it ?

i can get photos also, if more specific info is needed. I just dont like the idea of changing batteries all the time.
typically how long should a good stat last for ??

thank you very much for your reply

mark

[Ed Imeduc]

Be sure and get the common from the same transformer that is the one for the same zone the tstat is on dont mix the common to the tstat.


ED ;)