I have three zones and just turned the heat on in two zones yesterday for the first time. I have it set on a programmable thermostat for 66 degrees and at 10 pm to drop to 62. The heat came on fine and hit the desired temp. After a while I could hear the water flowing through the baseboard heaters again and it would not stop. I checked the thermostat and although it still said 66 the temp in the house had risen to 72! I turned the heat off completely yet the water kept running eventually sending the heat up to 77! Finally this morning I turned off the furnace directly and that put a stop to it. Is this a faulty thermostat? The heat in the 2nd zone worked fine, hit 66 and stopped. Thanks for the advice.

If your thermostat has backup batteries check them. This happened me a few weeks back and worked like a charm. One of the contacts had a bit of corrosion from the old battery and I cleaned it off with some sandpaper.