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Check out the conversation between me an a home owner with a Taco zone valve problem.

Home Owner: We have a question regarding our system. We have 2 zones, upstairs and downstairs. Upstairs thermostat was at 58, downstairs at 63. We turned upstairs up to 65 and since then have had no heat to the downstairs zone. This is what I have done to troubleshoot. We swapped both thermostats and the downstairs zone doesn't change, upstairs does work. We also disconnected the wires at the thermostat and crossed them, downstairs still does not work. I went down to the boiler and crossed the thermostats at the zone valve and still could not get the lower valve to work. I've opened the zone valve to the lower level and it works. It shuts down when it reaches the temp that the thermostat is set at for that zone. The only way to get the zone to work downstairs is to leave the zone valve open. The more I read it sounds like the system is air locked but that wouldn't explain how it works when the zone valve is open? Any suggestions would be great. Thanks, Justin.

I Forgot to mention, the system is BRAND new. It was installed 6 months before we moved in. Wiring, plumbing, thermostat and boiler are brand new. Thanks, Justin

Tom: Hi Justin, if the zone was air bound, you would not have any heat when you opened the zone valve.
So we can assume the zone is not air bound.

It sounds like the zone valve is not opening when the thermostat is calling for heat. If this is a Honeywell zone valve, try this. turn the thermostat up as far as it will go. then check the lever on the Honeywell zone valve, tell me if it moves very freely across, if it does the zone valve is opening when the thermostat is calling, but if there is any resistance on the lever, the zone valve is not opening, let me know the results of this test and I will give you more instructions. Thank you 

Peerless oil boiler Taco zone valve control Taco Zone Valve Close Taco Zone Valve

Home Owner: The zone valve is not a Honeywell; here are the model types of everything in case that helps. The zone valve control is Taco ZVC403, the two zone valves are Taco 571-2 and the thermostats are Honeywell PRO 1000 non-programmable. The levers for the zone valves don't move for either. The lever for the zone that's operating properly, zone 1, stays on auto whether or not it's running. The lever for the zone that's having problems, zone 2, stays on open (the only setting we can get heat) whether or not it's running. When the boiler kicks on for zone 1, both the lights for t-stat call and valve open light comes on. When it kicks on for zone 2, only the light for valve open comes on. Is there a test we can try for this model of zone valve? Or another suggestion you have to try? I'll attach a few pictures in case that also helps.

Tom: OK Do the same test on the Taco zone valve if the lever comes down easy the zone valve is open. only difference is a Taco zone valve takes 2 minutes to open. So turn thermostat all the way up as far as it goes wait 2 minutes ant pull the lever down, then let me know what happens.

 Home Owner: I went downstairs and closed the valve. When I came back up I turned the thermostat all the way up and waited for the thermostat to call for heat (heat on) I Went downstairs and the boiler was off. I manually turned the zone valve to the open position from the auto position and the heat works in the zone. (this is how we've had it for 3 days)  Is it harmful to leave the zone valve manually open?

Tom: Did the lever go down easy or did it have resistance?

Home Owner: It had resistance; the pressure was even throughout the motion of the lever.

Tom: Ok this means the thermostat is not opening the zone valve. Use a voltage meter to see if you have 24 volts at the number 1 and 2 terminals on the Taco zone valve. be sure the thermostat is turned all the way up when testing, let me know what you have.

Home Owner: I tested both zones and both came back at 26.5 amps using AC on the multi meter. That is with the thermostat all the way up, "heat on" in the display. Could it be something in the zone valve control? As my wife said the thermostat light does NOT come on when calling for heat at the zone. Also, there is a third zone on the control... Is it easy to switch over if that is the issue?

Tom: If you have voltage to the 1 and 2 terminals and the lever is hard to pull down, the head is bad, Just replace the head please see for instructions on replacing the head. The light on the control will not come on if the head does not open.

Home Owner: Do you happen to have the correct part? I Would like to purchase it from you considering all the help. It's the Taco 571-2 zone valve, all I see on the site is Honeywell. Do these happen to go bad often? Like I said the entire house was redone in April, this is the first year it's been used.

Tom: Sorry I do not have the part, but most plumbing supply have them and even some Home Depot have them

Home Owner: Thanks for all the help. I was able to change the part out and now everything is working. Should I grab another one of these and keep them on hand? I am Just surprised that something less than a year old could be junk, especially at the $80.00 price tag.

Tom: They are always readily available, but it's up to you. I have seen them burn up in a day, and I have seen them 20 years old, you can never tell with electronic parts.

Thank you for using the 24/4 Help Line

Thomas Petito Reardon