On Mon, 02 Apr 2012 22:31:04 -0400, frank1492
wrote:

I am back with a different themostat question.
I am trying to figure out why sometimes the temperature at the
thermostat (and thus in the house- single zone system) gets too high.
I just got a new digital thermostat and the condition persists.
Diagnosis is made more difficult because the condition exists in my
GF's house and I am only there periodically.
The house has an oil burner, hydronic heat and a 24VAC control
system (2-wire). The other night she claims to have come home and
found the setpoint at 65 when the actual temp was 70, and she claims
there was heat in the radiators. She also says the oil burner was
running at the time, but I told her that might be misleading since
heat emission is largely controlled by the circulators and the burner
might simply be needing to raise the temperature of the hot tap water.
(Note: This is in the NE where the temperature all day has been in the
40's.)

I suspect the circulator circuit may have a problem. The relay that
turns them on and off may be sticking in the "on" position.

There is also a valve in the system that will allow gravity to
circulate the water if it is opened. It should be up near the ceiling
and probably has a thumb screw on top of it.