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we have a three zone baseboard hotwater furnace. a few months ago one zone would randomly stay on, we did change the thermostat we have not noticed the problem again, but in another zone we have the same problem, we changed the thermostat & it has not helped, the heat stays on no matter what temp we set it on, we have to shut the furnace off. please help.

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You could have a mis-wired thermostat, or a bad zone valve. Have you tried it with the thermostat disconnected? – TomG Jan 2 '12 at 20:39
yes, we took the thermostat off the wall & the heat was still on. – candy Jan 3 '12 at 23:05

If you actually removed the thermostat from the wall, but the heat stayed on, more than likely the R wire is connected to the W wire somewhere in your system. Go to the furnace itself, and look at what is connected to the terminals on it. Try undoing terminals (one at a time!) until it stops, then continue troubleshooting from there.

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That's not the problem. The zone valve is not working. Zone valves stick either in the open or closed positions when they go bad. In your case bc heat won't go off its stuck in the open position. Need to replace zone valve

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That's assuming you have a valve system rather than a circulator-pump system. – keshlam Dec 17 '14 at 15:41

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