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Check the error code on the control board at the furnace. It could be a number of things. If the furnace is not lighting, it could be the ignitor If the furnace lights then goes out right away, it could be the flame sensor If the furnace lights then goes out after several minutes, it is a limit switch. Turn the tstat fan switch to on and see if the fan comes on, if it does not you have no power to the furnace, check the breakers or cutoff switch.

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Q: Why won't your Goodman heater model GMT090-3B start when the thermostate is turned up?
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