I have a 21 unit builiding with a hydronic heat system with zone valves in each unit. Hot water flows slowly in the unit I am in but does not respond to thermostat. Old low voltage thermostat had three wires green red and yellow. Old thermostat was connected with green to the R terminal
Red to the G terminal,
And yellow to the W terminal on the thermostat

Have new Honewell thermostat with R W and Y terminals

Any clue as to the correlation of the wires to what terminals

I don't think the old one was even wired correctly as most things in this building

Are the Zone valves hard to install?

If you have to install the complete zone valve you usually have to drain the boiler system and separate the old valve from the pipes then install the new valve. If you can find just a power head or a complete old valve just like the one you have then all you have to do is replace the power head. It does not require draining the system or messing with the pipes.

Brand of valve?
Exact and complete model number of valve?
I will see what I can locate as far as info is concerned.

If you have to install the complete zone valve you usually have to drain the boiler system and separate the old valve from the pipes then install the new valve. If you can find just a power head or a complete old valve just like the one you have then all you have to do is replace the power head. It does not require draining the system or messing with the pipes.

Brand of valve?
Exact and complete model number of valve?
I will see what I can locate as far as info is concerned.


Much appreciated quick response. That's what I thought. Got a good local supply store here in MN. But the building is about 50 years old. Some parts hard to find. Looks like a Honeywell Synchron 8927.
It was my understanding that these systems should have the air bled on a regular basis is this true?

Any idea on the funky wiring to the thermostat?

Thanks Again

The Synchron units is actually just the motor name not the valve number.They usually can just have the motor replaced or the end switch replaced. No need to remove the valve housing and mess with the pipe/water system.

The old thermostat is probably OK but you might need to fix the valve

I need the exact valve numbers letters to find you a wiring diagram. The Sychron number does not help. I believe 8927 is a code date for manufacturer.

The Synchron units is actually just the motor name not the valve number.They usually can just have the motor replaced or the end switch replaced. No need to remove the valve housing and mess with the pipe/water system.

The old thermostat is probably ok but you might need to fix the valve

I need the exact valve numbers letters to find you a wiring diagram. The Sychron number does not help. I believe 8927 is a code date for manufacturer.


That would be good if it was just the motor. Will have to tear into it tomoorow. Gave them a space heater for the night. The reason I started with the thermostat was that it seemed there was no repsonse when it was cranked up. Normally there is a rush of water. Also it is an old mercury thermostat and there is no spark when moving it up and down. Was just going to replace it as routine maintenance. Also in each unit there is the zone valve at one end where it comes into the unit and then pipes it's way to the rear where there appears to be a bleeder valve at there other end.

I managed another building where the zone valves were in the utility room with the pump and the rest of equipment and at least once in the middle of the winter they would come out and bleed the air from there.

My skills are more carpentry related and minor plumbing repairs and such but I try to learn as I go and observe the guys I hire out to it would be nice to tell the owner what to tell the pro needs to be looked at.

Thanks again. Do you just answer questions out of the kindness of your heart?

Do you just answer questions out of the kindness of your heart?

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