Reversed line-voltage polarity, a grounding problem, or reversed low-voltage transformer wires. Heating and cooling are both affected. The furnace will not start the ignition sequence until this is corrected.
York TG9S 9 red flashes is reversed line polarity, a grounding problem, or reversed low-voltage transformer wires. Heating and cooling both stop starting the ignition sequence until it is fixed. The manual also says to check that the flame probe is not shorted to the chassis. There is no filter step and no vent-pipe step on this code.
Likely causes
- Reversed line voltage polarity
- A grounding problem
- Reversed low-voltage transformer wires
- Flame probe shorted to the chassis
Safe checks for 9 red flashes
- Leave the furnace off if it will not light. Do not swap wires on the furnace
- Techniciancheck polarity at the furnace and the branch circuit, check furnace grounding, and check that the flame probe is not shorted to the chassis
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Call a licensed HVAC technician. Nine red flashes is an electrical fault, not a filter or vent problem.
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Parts & tools for this fix
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Multimeter for appliance and HVAC diagnosis: guide
In this code: Reversed line voltage polarity
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