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Bearcamp 12-24-2008 08:32 AM

Set thermostat to 50 and still gets 75 in home
I just bought this house and noticed it's really warm in here. Furnace is oil with baseboard hot water and boiler for hot water. So the thermostats were the old mercury filled ones and I replaced them with new. (not digital) It has 2 zones along with the Taco zone valves which look new. I set the downstairs stat to 60 and still the furnace runs til it's 70-75 in the downstairs although the upstairs seems to work fine. Also noticed the Honeywell aquastat was set at 150 on the high and low so I changed it to 150 low and 180 high. Settings on both thermostats are set to 4. Even when I turn the heat all the way down to 50 it still gets 70-75 in here. Correct me if I'm wrong but the furnace would still run to make hot water even if the room stat is turned to 50. I really need help to solve this issue as it's awful warm in here. Trying a new setting,,,,,,,,,,,I'm gonna set the upstairs stat to 68 and the downstairs to 64 to see if it will even out the heat without having all the heat downstairs.

beenthere 12-24-2008 02:47 PM

Probably have a bad zone valve on teh zone that is over heating.

Bearcamp 12-24-2008 03:45 PM

I thought possible also. But the wiring just seems like too much and don't know if the 2 are wired correctly. They have wires going from the stats to each zone valve and also coming from the aquastat. Which I believe is right. But the 2 stats are also connected by 2 wires. In other words, they are wired together. I'd like to find out if this is right or see a wiring schmatic for 2 stats, aquasta and 2 zone valves.

beenthere 12-24-2008 04:26 PM

Top off Taco zone valve has a wiring diagram.

kennzz05 12-25-2008 12:27 AM

if i remember correctly power from tformer should go to r at stat than back to zone valve thru w on stat(dont remember terminal designation use beentheres advise for that) than common from tformer goes to the zone valve, again youll have to dertermine where. finally the switched terminal on the zone valve goes back to the aquastat or to whatever turns the boiler on or starts the pump depending on how its set up . some boilers are set up to start the pump and fire it up at the same time and others only start the pump and rely on the aquastat so start and stop the burner so the waters always hot just not circulating if you said the two stats are tied togeather thats wrong one is going to override the other

AllanJ 12-25-2008 12:10 PM

Maybe the old mercury thermostats were not that bad after all. For a mercury thermostat you can see the connection make and break.

At any rate, with your new thermostats, when you turn the setting down on one, do the baseboards cool down after about a half hour? Then if you turn the setting back up do the baseboards heat up within 10 minutes?

Try each zone.

Measure the voltage across the terminals at the zone valve. When the thermostat is calling for heat a non-zero voltage should be measured, otherwise zero.

While you are at it you might see if both thermostats have to be turned down to get zero voltage across the zone valve. This could be either incorrect or intentional.

If there are more than two terminals with individual wires it's a bit tricky but in most cases one combination of two will have voltage only when the thermostat is calling for heat.

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