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Richard, Technical Manager
Category: HVAC
Satisfied Customers: 1514
Experience:  27 years of Experience, NATE Certified, professional trainer
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I have a Honeywell T8775A1009 thermostat that I was installing

Resolved Question:

I have a Honeywell T8775A1009 thermostat that I was installing on a hydronic heat system- however the thermostat runs through an Amtrol 91 zone valve and has three wires to the thermostat - this thermostat only has connections for two wires - without the third the valve won't open and circulation pump will not run. Do I need a different thermostat?
Submitted: 6 years ago.
Category: HVAC
Expert:  Richard replied 6 years ago.
Hello there is a way you can use the two wire stat but you will need to add a SPDT relay I can give you a digram on how to do it. Or here are a few thermostats you can use for 3 wire zone valves. Honeywell TH611D or White Rodgers 1F80-0471. You can google for prices both around the 50 to 60 dollar range. Thank you Richard.
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Customer: replied 6 years ago.
Will a thermostat with heat/ cool settings work? I was assuming that you would use the third wire as a "fan relay" connection. Thank you
Expert:  Richard replied 6 years ago.
Expert:  Richard replied 6 years ago.
Any two wire stat will work with that diagram cool does not play into it. With a 3 wire you need the B terminal.
Customer: replied 6 years ago.

Okay - I googled Honeywell TH611D - nothing. I am not keen on White Rogers but if it is the only one that will work - I'll try it. I was thinking a Honeywell TH5110D1022 might work if the "y" connection is used for the zone valve. It is generally the lead for the fan relay if you had a forced air furnace. I am asking if this thinking is flawed? If so, I guess I will have no choice but to add the spdt relay or install a new zone valve.

White Rogers 1F80-0471

Type: Millivolt
Wiring: Rc


Honeywell TH5110D1022

Type: Conventional
Heat Pump
Wiring: Rc
Changeover: Manual
Expert:  Richard replied 6 years ago.
hello if you go to it will list all the thermostats they offer are the DIY stores. Each will list what they are good for gas oil zone valves. Or you can go to , but there you would need a model and they have all the specs. Try the yourhome site first it will give you pictures so you can see what they look like. The one I was thinking might have been a th6110D . If you have any questions on any of them let me know Richard