Heating, Air Conditioning, Fridge, HVAC/no heat



Hi Mike,

I am hoping I can get some info on troubleshooting zones on a boiler system.  I have 3 zones…basement, main floor and 2nd floor, but one circulator.  They're controlled by 2 taco 571 zone valves and, I believe, a transformer that initiates heat in the basement.  The basement thermostat initiates heat right away.  The zone valves have a 90 second delay, which trigger the box on the boiler.  All three thermostats seem to signal the box on the boiler, but the main floor doesn’t initiate water flow.  I’d like to know how to test voltage on the zone valves to determine if that’s where the problem is.  There’s voltage at the transformer (27 volts), but not sure which terminals to touch on the zone valves.  I attached some pictures of the set up that I felt was relevant.  I can send pics of the honeywell box on the boiler, too, but i'm limited to two pics, it seems.  Thank you in advance.

Taco wiring
Taco wiring  
Please see the attached image.

With the thermostat calling for heat, you will have the 24 volts when your meter is on terminal 1 and 2 on the zone valve head.  Most likely, if you do not have power here, the problem is with the thermostat, or wire to and from the thermostat.

If you have power at 1-2, but the boiler does not engage you have a defective valve "head" which will need to be replaced.

Heating, Air Conditioning, Fridge, HVAC

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Mike Reavis


Questions related to "Wet Heat". This is heating your home, office etc. with radiators, panels, and convector apparatus. Steam and water heat. I can answer questions about boilers, piping,and associated parts of these systems. Please do not ask for specific information about how I feel about one boiler, etc. over another--These questions should be directed to a licensed contractor that you know of, or that your neighbors and colleagues look to to provide solutions.


I have 20 plus years experience, which has lead to passing my state master HVAC license.


Completed college

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I work on the manufacturer's side of the business currently

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