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I noticed tonight my furnace was firing up, but not actually blowing out heat. I turned the thermostat down so it was no longer triggering it, let it sit for a couple of minutes, and then turned it back up: it ran fine and started blowing warm air. This lasted for an hour, maybe two, then it happened again.

Is the igniter going bad?

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Could be. Could also be the flame sensor not working (if the control system can't tell that the furnace is lit, it will assume it's not and turn the fuel off.) Could be a nozzle clog (since you didn't specify your fuel - that's more of an oil than a gas problem.) Could be an issue with a power vent, or a power vent sensor (again, since no details provided, may or may not apply to your furnace.)

Unless you really know your way around them (and quite often even then) it's often a good idea to have a pro in to deal with fuel heating appliances - they have knowledge of the systems, and esoteric tools that don't make sense for a homeowner to purchase, such as the exhaust gas analyzer that allows adjusting the fuel/air mixture for best efficiency.

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Probably not, but it depends entirely on the make and model furnace.

In most furnaces the blower will only come on, if a flame has been sensed. Once a flame has been detected, either a timer, or another sensor tells the blower when to turn on. If the blower is on when there is not flame (other than a bit after the flame has gone off), there may be a problem with the high limit switch, or the furnace may be overheated.

Contacting a local, reputable HVAC technician is likely the best course of action.

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