New Thermostat for 3-wire System

An_Fo

I'm trying to update my thermostats around the house. They currently are old mercury-powered White-Rodgers, and I'm just looking to step up to anything newer.

The problem I am having is that the new Honeywell I put on doesn't turn the boiler off.

I have three White-Rodgers zone valves, and from what I can tell, they need a longer signal to start closing than just the thermostat stopping the heat call.

The old thermostat ran off of three wires: red, white, and green.

Touching the red and white together calls for heat, and the valve opens.

Touching the green to red for more than 5 seconds closes the valve. Any amount of time shorter than that, and I can hear the valve start to close, but if I release the wires, it doesn't continue closing.

With the new thermostat hooked up ( red to R, White to W, Green to G), when I stop the heat call the valve does not close, and the boiler just runs continuously. I've tried moving the wires to various other positions to no avail.

Am I missing something obvious? Are there other thermostats that might work? Other positions that I should try for the wires?

JUGHNE

What is the model number of the new HW tstat?
Do you have a wiring diagram showing heat only, series 20, using 3 wires? Then you go to installer set up for more directions.

An_Fo

Thank you, your questions led me to the answer. I need a SPDT t-stat, which the model I have is not.

JUGHNE

Simplest I know of is HW FocusPRO 5000 series. TH5110D1022.
Non programmable....might not be in the big box stores.

ChrisJ

JUGHNE said:

Simplest I know of is HW FocusPRO 5000 series. TH5110D1022.
Non programmable....might not be in the big box stores.

The 5000 can behave as a double throw switch? Disconnecting W and connecting something else?

ratio

Some of the cheap heat pump stats have a form C contact for the reversing valve, but the internal logic might not allow it to work. Best bet would be to add a simple single pole double throw relay powered from the W terminal. That would convert the signal to what you need. Another option might be a Honeywell TrueZONE panel, if you have more than one zone. The outputs of the zones are form C.

JUGHNE

According to the paper.....tstat R goes to valve R.....tstat Y goes to valve W.......tstat W goes to valve B.
Then in programming for system type you select #2. (3 wire zone valves-series)
Then it switches with R as the common from Y to W.
Just like the mercury bulb with a contact on each.

Never did one....just now read the book.

ChrisJ

JUGHNE said:

According to the paper.....tstat R goes to valve R.....tstat Y goes to valve W.......tstat W goes to valve B.
Then in programming for system type you select #2. (3 wire zone valves-series)
Then it switches with R as the common from Y to W.
Just like the mercury bulb with a contact on each.

Never did one....just now read the book.

If that's the case, and a non-programmable stat is what's wanted.

http://www.supplyhouse.com/Honeywell-TH5110D1022-The-FocusPRO-Large-Screen-Non-Programmable-Digital-Thermostat-Premier-White-4088000-p


I assume the 6000's also do it?

http://www.supplyhouse.com/Honeywell-TH6110D1021-FocusPRO-Programmable-Thermostat-1H-1C-Large-Display-4077000-p

JUGHNE

Those papers indicate that series 20 system also.
But apparently no AC?
You are using the Y term for the third heat control wire.