While the furnace was operating, the pressure switch opened four times during the call for heat. The furnace locks out for one hour and then restarts.
York TG9S 6 red flashes means the pressure switch opened four times during one call for heat. The furnace locks out for an hour and then tries again. Causes in the manual are a faulty inducer, a blocked vent pipe, or a faulty pressure switch. Three red flashes is the switch that never closed at the start. Six is the switch that opened again and again while the furnace was already running.
Likely causes
- Faulty inducer
- Blocked vent pipe
- Faulty pressure switch
Safe checks for 6 red flashes
- Look at the outdoor vent pipe for a blockage. The one-hour lockout is not a repair
- Techniciancheck the inducer, the vent pipe and the pressure switch
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Call a licensed HVAC technician if 6 red flashes return after the vent pipe is confirmed clear.
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Parts & tools for this fix
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Furnace pressure switch: guide
In this code: Faulty pressure switch
This one is for a technician to test or replace, so we only explain it and do not link to buy it.
Furnace inducer (draft) motor: guide
In this code: Faulty inducer
This one is for a technician to test or replace, so we only explain it and do not link to buy it.