"john" wrote in message
Quite frequently the furnace will go off immediately after firing up
with an accompanying odor of gas. My HVAC professional said that this
was due to the fact that it was a "flash" start with virtually no burn
time and that a small amount gas remained in the air but was harmless.
Nevertheless, I don't like it. I will be looking at the 9400 and
asking questions on how it functions before I purchase.

Are you sure it is the thermostat? Could be the differential on the heater
is not set right. In a hot water system, the thermostat tells the heater
that the room needs heat. That starts the circulator pump moving the
already heated water through the system.

OK, the water is circulating but it is cooling off as it gives its heat up
to the room. So, the sensor in the heater tells the burner to start. It
will burn until the water is heated up enough and then shut off. Then the
cycle is repeated as the water temperature goes down. This can happen a few
times during a heating cycle. If this is not adjusted properly the burner
will cycle too often or not often enough. You may have problems other than
the T stat.
Ed