furnace runs past set temp. on the thermostat - http://www.hvacmechanic.com/ Forums
Original message
| cav
 |  "furnace runs past set temp. on the thermostat"
, posted Fri 27 Oct 08:33  
We turned on the heat for the first time about to days ago and set the thermostats to 65. The heat in the house downstairs is now 72 and upstairs is 78. We have a weil-mcclain oil fired furnace. Hot water baseboard heat. Furnace heats our water and all was fine till we turned on heat. The furnace was serviced in July and has had no problem till now when I turned on the heat. Keeps running and goes off and on and off, etc. I played with the thermostats and set them above the temp. they were showing and they would click. Put them lower and they would click. Anyone have any ideas? At the price of oil I don't want to use the seasons fuel in a month. Thanks, cav
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Replies:
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| Freon
| "Re(1):furnace runs past set temp. on the ther" , posted Fri 27 Oct 13:28
Did your heat work fine last year or is this temperature overshooting a continuing problem? Have you had any work done on the electrical system. Any bad thunder storms over the summer? It could be the heat anticipator setting but if it worked fine last season and no one has played with the system, the setting should not have been affected.
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| | cav
| "Re(2):furnace runs past set temp. on the ther" , posted Fri 27 Oct 14:32
Everything was fine last year and this year until April when we turned the heat of. In July we had it cleaned and when we turned the heat on is when we started having this problem.
Thanks, cav
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| | Freon
| "Re(3):furnace runs past set temp. on the ther" , posted Fri 27 Oct 14:36
When you want to heat the house, you say the boiler comes on and then shuts off, then on etc.. Approximately how long are the run times and off times? Do the circulator pumps continue to run while the boiler is in a Off cycle? What type of thermostat do you have?
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| | cav
| "Re(4):furnace runs past set temp. on the ther" , posted Sat 28 Oct 09:24
The run times are anywhere from 5-10 minutes. Off times are anywhere from 1/2 hour to 1 1/2 hours. I have Rite Temp thermostat downstairs and replaced the upstairs with a honeywell. Not sure about the circulators.
thanks
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| | Freon
| "Re(5):furnace runs past set temp. on the ther" , posted Sat 28 Oct 12:14
You need to be sure when each thermostat is calling for heat that each zone valve opens and then when the thermostat is not calling for heat, each zone valve closes. Usually there will be one circulator pump and two zone valves, one for upstairs and one for downstairs, but check your system. With both thermostats set at less than the room temperature, the circulator should be off and both zone valves closed. My thought is if the zone valves are not closing then you may be having convective heating. The zone valves are important.
If it's hard to tell if the valve is closed, set the thermostats much lower than room temperature so there is no call for heat for at least an hour. Then CAREFULLY touch the feed water pipe about 4 feet away on the downstream side of the zone valve. If it's cool, the valve is most likely closed. If it's hot then the valve may be open.
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