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Old 09-20-2009, 10:57 AM   #1
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3 wire thermostat

I am trying to replace a broken thermostat. It is a 3 wire White Rogers, one of three zones to a hot water boiler heating system. One wire is red, one is blue, and the last is white. Every thermostat (programmable) I buy has slots for 4 wires. Can I leave a slot open? I don't have a cooling system.

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Old 09-20-2009, 03:29 PM   #2
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Location: West Michigan
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3 wire thermostat

For a three wire zone valve, the stat needs to have a contact that closes when when the call for heat is complete. The zone valves power open with a call for heat and power closed when the call for heat is satisfied. The average 4 wire digital heat and cool stat will not work for this application. There are some that will accomplish this but are usually more high end.

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Old 09-20-2009, 04:30 PM   #3
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3 wire thermostat

So what can I replace the thermostat with? One is completely shot, the others are just really old and I would like them updated.
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Old 09-20-2009, 07:37 PM   #4
An old Tradesmen
Join Date: Oct 2008
Location: PA
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3 wire thermostat

White Rodgers has stats that you can use. Don't remember the mod numbers off hand.
You may want to search their website.
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3-wire, heat, thermostat

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