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Do you have zone valves?
Then you could have a faulty zone valve. The zone valve may be sticking open or have a bad end switch. It's the end switch in the zone valve that pulls in the burner and circulator. Another possibility is a short in the thermostat wiring between the thermostat and the zone valve.
How can I test this?
disconnect the thermostat wires from the problem zone (valve) when the zone is running wild. If the burener shuts down
then you have a short.
If the burner and circulator continue to run then the problem is probably in the zone valve
Keep in mind there is a time delay (a minute or 2) after the disconnect before the zone valve will shut things down. Do this when no other zone is calling
How do I identify the zone valve?
You have to trace the wire from the thermostat to the zone valve. If that's not feasible you need to run the other zones one at a time to identify which is which.
What brand of zone valves do you have?
Does Taco sound correct. Kind of hard to read.
If the head is green or gold then Taco is right. When the valve is open you will feel no resistance when you push the lever down that's on the side of the head
One of the valves(marked #1, although problem is on 2nd floor) is stuck. The other 2 move down about 2/3 of the way before I feel resistance. The other valves are marked 2 & Kit - for kitchen apparantly. The one that's stuck also looks like corrosion is forming on the outside of the valve.
If this valve corresponds to the problem zone (I suspect so) then it needs to be replaced. Normally when these valves fail usually all you need to do is replace the head but if you see corrosion on the valve body (the brass part) then the entire valve needs to be replaced
any more questions?
Just 1 - how do I replace it? Any welding necessary?
You need to drain down the system, cut the old valve out and yes you would need to solder the new valve in place
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