York furnace 3 double red flashes: Second stage pressure switch stuck open
Three double red flashes means the second stage pressure switch did not close when the furnace called for high fire. Low stage usually still works, so the symptom is reduced output rather than no heat.
Applies to: York, Luxaire and Coleman two-stage gas furnaces using the UTEC integrated furnace control boards documented in technical service letter ST-045-09. Single stage boards do not use this code. Stored in the error code array.
What it means
A two-stage furnace carries a separate pressure switch for high fire, because the higher firing rate moves more combustion air and needs its own proof of draft. York distinguishes this from the first-stage failure by pattern rather than count — three double flashes rather than three single. The practical consequence is easy to misread: the furnace is not dead. It runs on low fire, which in mild weather may be entirely adequate, so the fault often goes unnoticed until the weather turns and the house cannot keep up.
Most common causes
- The second stage pressure switch failed and no longer closing.
- The sensing hose to the second stage switch disconnected, kinked, or blocked.
- The inducer not reaching high stage speed.
- A partly restricted vent or intake — adequate for low fire, insufficient for high fire.
- A partly blocked condensate drain, which restricts more at the higher rate.
- The two pressure switches swapped during a previous repair.
- A wiring fault in the second stage switch circuit.
How to diagnose it
- Confirm the pattern is double flashes rather than single — that is what separates this from the first stage code.
- Note whether the house heats slowly rather than not at all, which fits this fault.
- Check the outside vent termination, since a partial restriction produces a high-stage-only failure.
- Check the condensate drain for slow drainage rather than complete blockage.
- Note whether the fault followed a service visit, since swapped switches are a real cause.
How to fix it
- Clear the vent termination and condensate drain if either is restricted.
- The pressure switches, hoses, and inducer are technician work.
- Have the technician confirm the switches are fitted the right way round if the furnace was recently serviced.
- Do not simply live with low fire. The partial restriction usually worsens and eventually affects low fire too.
Notes
A furnace stuck on low fire is easy to tolerate in mild weather and impossible in a cold snap. Acting when the code appears rather than when the house stops keeping up is typically several weeks cheaper.
Related
All codes for this manufacturer
York, Luxaire and Coleman furnace flash codes — every code, with what differs between models.