York TM9V080B12MP11 Error Code 13 Red Flashes: High-Fire Pressure Switch Open
What Does Code 13 Red Flashes Mean?
This two-stage York furnace uses a separate high-fire pressure switch to prove venting is adequate when the furnace steps up to its higher firing rate. Because high fire moves more combustion gas, that switch has a tighter setpoint and needs more inducer draft to close than the low-fire switch. When the board commands high fire but the high-fire switch stays open, it sets this code; the furnace may still run at low fire but cannot deliver full heat.
The manual is specific about the order of checks: look for a partially blocked vent pipe or a loose or disconnected wire before replacing the pressure switch. A partial restriction is the classic cause here — it may pass enough draft for low fire and its switch, yet fall short of what the high-fire switch demands. On a condensing furnace, a condensate-holding sag or a partly obstructed termination can create exactly that kind of load-dependent shortfall.
This is distinct from the 3 Red Flashes code, which is the main pressure switch failing to close so the furnace will not ignite at all. Thirteen flashes is narrower: ignition and low-fire operation can be fine, but the high-fire stage specifically cannot be proven safe to run.
What You'll Notice
- The furnace heats but seems stuck on low fire, never stepping up on cold days.
- The home under-heats or takes much longer than usual to reach the setpoint in cold weather.
- The code tends to appear after the furnace has run a while or when high demand calls for high fire.
- Low-fire cycles may complete normally while high-fire attempts fault out.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Partially blocked vent pipe | Most common | ✗ Call a pro → |
| Loose or disconnected wire to pressure switch | Common | ✗ Call a pro → |
| Faulty high-fire pressure switch | Common | ✗ Call a pro → |
How This Is Diagnosed
Following the manual's order, a technician first checks the vent and intake for a partial restriction — including a condensate-filled sag on this condensing furnace — since that is the most common cause and can be load-dependent. Next they check the high-fire pressure-switch wiring for a loose or disconnected lead, and verify inducer draft when the furnace is commanded to high fire. Only after those pass is the switch itself metered and replaced. A homeowner can safely check the outdoor termination for snow, ice, or debris, but confirming high-fire draft and testing the switch is technician work, which is why this is not a do-it-yourself repair.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The furnace only runs on low heat and will not step up to high fire even on very cold days.
- The outdoor vent and intake look clear but the 13-flash code keeps returning.
- The inducer sounds weak or strained when the furnace tries to reach high fire.
- You see loose wiring near the pressure switches or water pooled in the vent piping.
Frequently Asked Questions
Why does my two-stage York furnace only run on low heat now?
The high-fire pressure switch is not closing, so the board will not let the furnace run at its higher firing rate. It can still operate on low fire, but it cannot prove venting is adequate for high fire.
What should be checked first for a 13 red flash code?
Per York, check for a partially blocked vent pipe and a loose or disconnected pressure-switch wire before assuming the switch itself is bad. A partial vent restriction is the most common cause.
How is this different from a 3 red flash code?
A 3 red flash is the main pressure switch failing to close, so the furnace won't ignite at all. A 13 red flash is specifically the high-fire switch, so the furnace can still run on low fire but not high fire.
✓ Verified against manufacturer service manual — March 2026