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I have six zone valves that work fine and one that stays on 24/7. I have replaced the upper motor and the lower black ball, in addition to replacing the thermostat. None of that made a difference. The heat runs relentlessly.

What else could be going on?

Sadly, I do not have the kind of zone valve with a visible microswitch. Mine has two springs, on the right and left, that impede my view. I will try the suggested power test next, and report back, but I’m going to change out the power head first.

isherwood
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Susan Arth
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1 Answers1

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Some Honeywell zone valves contain a microswitch that closes (makes contact) when the valve reaches full open. It looks like this:

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(The picture shows the zone valve head without the valve body. I've placed a red dot on the part of the switch that moves from contact with the swing arm, which is the brassy-looking part attached to the spring.)

That switch can directly control the pump or the boiler. If your zone valve includes that switch, have you tested it to confirm that the switch electrically opens and closes as designed? There should be a click and the switch's continuity will change.

If the switch is stuck closed and it's wired for control, the boiler/pump will run constantly.

Photo credit

MTA
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