Good afternoon,

My house is heated with an oil furnace providing heat to a hot water baseboard system. For the last little while, I noticed the burner kicking-in for a few second when the thermostat send the signal (close the circuit) and stop with a second or two. When it does that the water temperature is already at its maximum setting. After the water circulate and the temperature lower to the minimum setting the furnace start and run as it should be. Before, when the signal was sent by the thermostat to start, the water circulating pump would run until the water had reached a minimum value setting and only then the burner would start. Does anybody know why the burner kick in and out so early in the cycle and what I can do to stop this behavior?

Thanks

P.S. all my themostats (3) are simple two wire, mercury contact units. No fancy electronic here.

Sorry, I would need a detailed schematic of wiring to tell why this could be, there are to many ways these things are wired in the factory and in the field.

Problem solved,

I did more investigation last night and found that two of the three zones valve's switch where not making contact properly. One was just too dirty (soot from contact spark) and the other was only making contact as the actuator was activated. At the end of the actuator course the contact would terminate and the burner stop. This is why the furnace would only start for a second or so before shutting down. I cleaned the contacts and every thing is working ti-gi-di-boo.

Thanks Northern Heat for your reply

Have a nice cold winter...