Sticky relay and open flow check are high on my list!
(The thermostat wire is plastic coated.)




On Tue, 03 Apr 2012 19:18:03 -0400, RBM wrote:

On 4/2/2012 10:31 PM, 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 can't supply other details except that she says sometimes this
happens, sometimes it doesn't. Also she claims she can "always get the
heat to stop if she manually resets the setpoint." (Don't know quite
how to interpret that.)
The only thing I can think of is that there must be a problem
with the oil burner control module, perhaps a sticky relay. Your
thoughts?
Let me know if further information is needed.
Thank you.
Frank

From your description, it sounds like a very basic hydronic system with
a domestic hot water coil. The only parts of that system that could
cause overheating would be a faulty thermostat, which was pretty much
ruled out, possible sticking circulator relay, although doubtful, an
intermittent shunt on the thermostat cable. If it's a very old cloth
wrapped cable with cloth wrapped conductors, this is a pretty good
possibility. The last possibility would be an open flow check valve.
Crank the valve closed, then open it one turn.