Zone Valve Stuck Closed?

Old 11-08-19, 07:02 AM
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Question Zone Valve Stuck Closed?

Hi, I'm pretty good at troubleshooting these systems, but have only worked on systems with circulators. My friend's house has a system with 3 zone valves (basement, 1st, 2nd). Controlled with a Taco ZVC403.

1st floor heat works fine. 2nd floor doesn't. Didn't know if the basement works because there is no thermostat down there at the moment. When I was down there watching how the zv works with the 1st floor, there was a 90s delay between the time thermostat asked for the heat and the zone valve opened and circulator turned on. Is this delay normal?

When I turn on the 2nd floor thermostat, the yellow light for the thermostat turns on on the ZVC, but the red light saying the zv is open never does. The power head does get hot.

I swapped the 1st and 2nd floor power heads, leaving the wires where they were (so 1st flr thermostat controls 2nd flr heat). And it worked fine. I saw a lot of things online about them failing stuck open, but not too much failing stuck closed.

For fun, I put the basement zone power head on the 2nd floor valve, and wired it accordingly. I turned on the 2nd floor thermostat and the power head got hot, then after about 3 mins, the red light started to show up on the ZVC, but it was very faint. The circulator never came on. The red light was not as bright as the 1st floor was. I guess the basement zone power head is bad too.

Obviously a new power head is needed. My real question was, is the delay normal, even for the 'working' 1st floor? Or is that one about to fail too?
Old 11-08-19, 10:22 PM
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As the zone valves get older they can open slower. I don't think 90 seconds is out of line. The head itself can get hot from just the hot water in the pipe. The valve must open fully for the circulator to work.

If you switched a working head to a valve and it didn't work properly...... the valve may be internally bad.

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