Winter is coming (45° this morning 
), so I had better get this thing fixed ....The unit is on my Burnham oil boiler, which is tied into my stoker - I need this unit to work since it controls heat calls to the baseboards upstairs, while the stoker provides the heat instead of the oil burner.
Here's the problem:
The circulator for my 3 heating zones is now running non stop 24/7. I had to disconnect the thermostat wires from the TT lugs in the aquastat to get it to stop. If I even momentarily connect the wires back to the TT lugs, the TT LED will light, which commands C1 to energize, running the circ non stop. That just happened out of the blue one morning - I woke up and could hear the circ running through the convergence of pipes in the closet in my bedroom.
I figured this to be a simple upstairs thermostat that was stuck .... but none of the zone valves are open! They're the old school mercury ones, so not much to fail there. I still see the little spark in the mercury when I crank it to 80°, then immediately back to 40° shutting down the heat call. The thermostat's wiring goes directly to the zone valves, then off there to the aquastat. There's also a 24v transformer in there as well that sends juice up to the t-stats, and back during a heat call.
I put my meter on the 2 leads in the aquastat that connect to the TT lugs - no DC voltage. Continuity test across the 2 wires acts like a condenser in a points ignition engine - it starts off very high resistance (in the million ohm range), then slowly comes down a little ... and then begins to rise again to infinity (no continuity). Seems normal to me ... ?? Checked for a short between either wire to the metal housing and the boiler itself. Nothing - no continuity. I should mention that I did these tests with one wire still connected to the aquastat TT lug - I may have to remove that one and test again.
Does this sound like a faulty aquastat? I installed it in '06, so it's been in the damp basement nearly 10 years now.
