All of the sudden, my Honeywell zone valve opens all the time even with thermostat lowered.

Choose two colors of the thermostat wire, and connect them to the NO and COM and connect them to the zone control board leads for the zone intended. Almost all zone valves spring return open when deenergized. So ensure the zone valve is open with the system is off. At the base of zone valve there is a set screw that needs to engage the damper valve shaft in the open position with the motor in the spring release position. Most zone valve are 90 degree moment from full open to full shut. If you have a Carrier zone valve, they go full open to full shut in 45 degrees of motion. Your open stop need to be set so the valve stops in the full stop position.
To help understand the operation of a zone system, say you have 2 zone system and zone 1 thermostat initiates a heat or cool demand. Zone 2 valves energizes and shuts and zone 1 stays open and allow air to heat/ cool zone 1. If zone 2 thermostat simultaniously initiates the same heat/cool demand, the zone 2 valve opens and both zone heat/cool. When either thermostat is satisfied the opposite zone valve closes and when both thermostat are satisfied both zone valves open.
Hope this helps you understand zone operation. The same works for higher multizone systems.

Yes, you can replace your thermostat with the Honeywell RTH6350 Model.

Have your zone Valve checked It has nothing to do with the Thermostat or zone pump.

Its hard to say where its getting power from. It should be a normally closed two wire valve, so power must be fed from the tstat only? Not real sure how it's wired. You could try a round of MUSICAL THERMOSTATS? That would answer your question as long as its played properly.

Good clues to work with--
Let's review how you wired up the Zone Valves, in relation to the Boiler Control panel...

You say the upper zone does NOT SHUT DOWN--
Does that mean it is OPEN ALL THE TIME?-- (even when the circulating pump is OFF? )
That sounds like the thermostat is not even in the circuit, then.

Have you been able to cycle each of the valves thru their cycles-- Open- and then closed?
-- It almost sounds like you have an interconnection between the two valves-- is this possible?

Each Thermostat has to control its valve only...
and most systems do this thru a control panel at the boiler--
So-- How is your control panel connected to the 2 thermostats, and how are the 2 zone valves connected to the Control board?

Are you following a wiring schematic for hooking the valves and thermostats to the control board?
There should be a schematic with the new valve you must installed, right?
did you wire it like the instructions showed?

Make a few more tests, and get back with us--

Mack B

I have only seen one Honeywell thermostat that would work with a 3-wire heating system.

I would replace it with a White-Rodgers 1F80-0471. They are about $100, but they are a good thermostat, and they work well with the 3-wire zone valves.

Most other thermostats have the "Y" terminal that you need, but do not control the zone valve correctly.

Helping Hands Services
- Fairbanks, Alaska -

Hi there, this mechanical t-stat you are using now, does it just open and close this zone valve on a call for heat to fire the burner also? What voltage is this thermostat, 24, 120, or even 220 volts? I need to no this so I can locate the stat you need to replace the old mechanical stat. Let me know exactly what all this stat controls, any fan, or just the burner and zone valve. I need to know the wiring configuration of the existing stat. This will make for a faster locating of the new stat. I can get you a stat that you can control just about any combination's of what ever and that's why I need to know voltages and amount of wires available to me to work with. This I thank you for. Contact me and I will get to you as soon as I am available today.
Sincerely,
Shastalaker7

The zone valve when there is a call for heat opens and the lever should give you no resistance. I am curious to know if other zones are heating ok. You could have a bad circulator or a frozen zone.

Hello. Each zone in you home has one thermostat controlling one zone valve. Generally, when a thermostat is calling for heat the zone valve opens and the circulating pump comes on to move the water around that loop. If your other two zones are both working as they should and you now have a new zone valve on the third loop I would suspect that the thermostat is faulty. Regards, Joe

Sound like there are running on emergency heat which is elrctric.Have the system checked out buy a local heating and cooling company. Have they checked the filter and changed them.