I changed my thermostat i changed the flame sensor i changed high limit . w...

i changed my thermostat i changed the flame sensor i changed high limit . why is my furnace not lighting

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svfixer avatar
2 months ago #2
Blogs: 57
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The thermostat is nothing more than a temperature sensitive on/off switch. If the cycle starts, it's not the t-stat.

T-stat calls for heat.....if diaphragm switch is open, inducer fan blower starts......this pulls a vacuum at the diaphragm, allowing the switch to 'close' which allows power to the ignitor......ignitor heats to reddish/orange and allows power to the gas valve......gas flows to burners, which ignite......if flame sensor is satisfied with gas burn at farthest burner from ignitor, burn continues until a preset temp. in the heat exchanger closes a switch to start the main blower.....warm air circulates throughout the heated space until the set temp. on the t-stat is reached to shut down the cycle until the room temp. returns to the 'call for heat' again....this is usually a 2 degree differential.

2 months ago #3
Blogs: 3
Forum: 4,044
Votes: 63

Here is a video of a start up cycle, watch it and see if it helps you trouble shoot. http://gasfurnacestartupsequence.blogspot.com/

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