Gas furnace does not shut off

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wphilden

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My gas furnace blower will not stay off when the t-stat reaches set temp. Here's what's happening. When I turn the t-stat to heat both the blower starts slow then half a second later it's on high. Next I can hear the flames come on. In about a minute heat comes through the vents. Once the house temp reaches the t-stat temp setting the blower shut's off for about 2-3 seconds then starts back up. After about 5 seconds the air coming out from the vents start to cool down. Once the house temp goes below t-stat set temp the blower shuts off or about a 1 second then the blower and the flames come on. Then this cycle repeats. The only way to get the blower to stop is the turn the t-stat to off.

Can any one please help me ?

Thanks,
Phil
 
Thermostats usually have the option of turning the fan on all the time, or just when the furnace is heating. On my thermostat it's labelled Fan: Auto, Fan: Cont. (continuous). (There may be a further option of hi speed when heating, low speed when not heating.) With today's digital thermostats you may have to search thru several menus to find the fan setting.

Or, the furnace may use up to 5 wires to the thermostat; if the thermostat cannot use all the wires, the furnace may consider an unconnected wire to be active. If the Fan-Continuous wire is unconnected it might cause this.

You will need to check your furnace schematic diagram or installation instructions to see what's needed, and compare it to the thermostat. Maybe something is miswired or loose.

Good luck with it.
 
Thanks for the reply. The T-stat was working fine before this started happening. I didn't change anything on the wiring but I did check and tighten all the wires to make sure they weren't loose. Still the same.
 
I traced the T-stat wires from the furnace to the T-stat. There was a splice in the line in the wall. The wires were bare and wrapped in old painters tape. The tape came apart and the wires were touching. I ran new wire and reconnected the wires and now it runs great !

Thanks for your help.
 
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