What causes York Gas Furnace 3 red flashes?

The inducer (combustion air blower) motor isn't running or isn't running at full speed. A blocked vent pipe or vent terminal, for example from snow, ice, leaves, a bird or animal nest. On condensing (90%+) furnaces, a blocked combustion air pipe or intake terminal. On condensing furnaces, a blocked condensate drain, trap or drain piping (York's Y91E pressure switches monitor the condensate drain system too). A cracked, split, disconnected or water-filled pressure switch hose. Loose or disconnected wires at the pressure switch or inducer. A faulty pressure switch.

How do I fix York Gas Furnace 3 red flashes?

Confirm the code: count the red flashes through the view port before turning off power, since a power reset clears the current flash. Three flashes, a 2-second pause, then repeating is code 3. Start a heating call and listen: if you don't hear the inducer motor start at the beginning of the cycle, the inducer or its wiring is the likely problem. Go outside and check the vent and, on condensing furnaces, the intake pipe terminals. Clear snow, ice, leaves or nests from the openings. With power off, look at the rubber hose running to the pressure switch. If it's disconnected, reconnect it; if it's cracked, split or has water in it, it needs replacing. York notes the hoses should be routed so condensate can't get into the switch. On a condensing furnace, check that the condensate drain and trap aren't clogged and that water drains freely. Never jumper, bypass or adjust the pressure switch to make the furnace run. York's manuals warn that doing so lets the furnace operate under potentially hazardous conditions. Don't open the vent system or try to repair the control board; York says controls aren't field repairable and should be replaced.

When should I call a pro for York Gas Furnace 3 red flashes?

Call a technician if the code returns after the vent, intake, hose and drain checks, or if the inducer doesn't run. A technician checks inducer operation, the vent and intake piping, the pressure switch hose and wiring, and tests whether the pressure switch closes, then replaces the inducer or pressure switch with the correct parts for your model. York's boards store recent fault codes. With no thermostat call active, a technician can press the LAST ERROR (or SW) button to replay the last five codes, which helps show whether the problem keeps coming back. Because a draft problem can let combustion gases back up, any repeated pressure switch fault is worth a professional check of the venting.

Code: 3 red flashes🔥 York Gas Furnace

York Furnace 3 Red Flashes: Pressure Switch Didn't Close (Meaning, Causes, Fixes)

Q: What does York Gas Furnace 3 red flashes mean?

Three red flashes on a York furnace control board mean the pressure switch contacts are open when they should be closed: the inducer (draft) motor was turned on, but the pressure switch never proved draft, so the furnace won't go on to ignition. York's manuals point to a faulty inducer, a blocked vent pipe, a broken or disconnected pressure switch hose, loose pressure switch or inducer wires, or a faulty pressure switch. On condensing furnaces, a blocked condensate drain or blocked combustion air pipe can cause the same result. York (Johnson Controls) furnace boards show faults with an LED behind the clear view port in the blower door. Fault codes flash on and off the number of times equal to the code, with a 2-second pause between codes, so 3 red flashes is code 3. York's Y91E condensing furnace installation manual defines 3 red flashes as: the pressure switch contacts are open when they should be closed. Older York manuals (for example the PC, PS9/FC9S and GM9S series) word it as: the normally open pressure switch contact did not close after the inducer was energized. Each heat cycle, the inducer starts and pulls air through the burners, heat exchanger and vent; the pressure switch only closes when it senses that draft. If it stays open, the board won't open the gas valve. That's a safety feature, and York warns never to bypass or adjust the pressure switch to make the furnace run. It's different from 2 red flashes (the switch is closed when it should be open, at the start of the cycle) and 6 red flashes (the switch opened repeatedly while the furnace was already running, which triggers a one-hour lockout).

Reviewed 2026-10-23 · Based on 3 manufacturer & service sources

What the code means

York (Johnson Controls) furnace boards show faults with an LED behind the clear view port in the blower door. Fault codes flash on and off the number of times equal to the code, with a 2-second pause between codes, so 3 red flashes is code 3. York's Y91E condensing furnace installation manual defines 3 red flashes as: the pressure switch contacts are open when they should be closed. Older York manuals (for example the PC, PS9/FC9S and GM9S series) word it as: the normally open pressure switch contact did not close after the inducer was energized. Each heat cycle, the inducer starts and pulls air through the burners, heat exchanger and vent; the pressure switch only closes when it senses that draft. If it stays open, the board won't open the gas valve. That's a safety feature, and York warns never to bypass or adjust the pressure switch to make the furnace run. It's different from 2 red flashes (the switch is closed when it should be open, at the start of the cycle) and 6 red flashes (the switch opened repeatedly while the furnace was already running, which triggers a one-hour lockout).

Likely causes

The inducer (combustion air blower) motor isn't running or isn't running at full speed
A blocked vent pipe or vent terminal, for example from snow, ice, leaves, a bird or animal nest
On condensing (90%+) furnaces, a blocked combustion air pipe or intake terminal
On condensing furnaces, a blocked condensate drain, trap or drain piping (York's Y91E pressure switches monitor the condensate drain system too)
A cracked, split, disconnected or water-filled pressure switch hose
Loose or disconnected wires at the pressure switch or inducer
A faulty pressure switch

Safe DIY checks

⚠ Before you start

Turn off power at the furnace/HVAC service switch and the breaker before opening panels. Shut the gas valve before any work near the burners, and never disconnect or alter the gas line. If you smell gas, leave the house and call your gas utility.

Confirm the code: count the red flashes through the view port before turning off power, since a power reset clears the current flash. Three flashes, a 2-second pause, then repeating is code 3.
Start a heating call and listen: if you don't hear the inducer motor start at the beginning of the cycle, the inducer or its wiring is the likely problem.
Go outside and check the vent and, on condensing furnaces, the intake pipe terminals. Clear snow, ice, leaves or nests from the openings.
With power off, look at the rubber hose running to the pressure switch. If it's disconnected, reconnect it; if it's cracked, split or has water in it, it needs replacing. York notes the hoses should be routed so condensate can't get into the switch.
On a condensing furnace, check that the condensate drain and trap aren't clogged and that water drains freely.
Never jumper, bypass or adjust the pressure switch to make the furnace run. York's manuals warn that doing so lets the furnace operate under potentially hazardous conditions.
Don't open the vent system or try to repair the control board; York says controls aren't field repairable and should be replaced.

🛠 When to call a pro

Call a technician if the code returns after the vent, intake, hose and drain checks, or if the inducer doesn't run.
A technician checks inducer operation, the vent and intake piping, the pressure switch hose and wiring, and tests whether the pressure switch closes, then replaces the inducer or pressure switch with the correct parts for your model.
York's boards store recent fault codes. With no thermostat call active, a technician can press the LAST ERROR (or SW) button to replay the last five codes, which helps show whether the problem keeps coming back.
Because a draft problem can let combustion gases back up, any repeated pressure switch fault is worth a professional check of the venting.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Furnace pressure switch (exact OEM part for your model)

Only after testing shows the switch doesn't close with proper draft. High-altitude installs may use a different switch.

Search eBay →

⚙

Pressure switch hose / tubing

If the existing hose is cracked, brittle or split.

Search eBay →

⚙

Furnace inducer motor (exact OEM part for your model)

If the inducer doesn't run or is weak. Model-specific.

Search eBay →

⚙

Carbon monoxide alarm

Recommended in any home with a gas furnace, especially with a venting problem.

Search eBay →

Sources

Last reviewed 2026-10-23. Always confirm against the manual for your exact model number.

York Furnace 3 Red Flashes: Pressure Switch Didn't Close (Meaning, Causes, Fixes)

What the code means

Likely causes

Safe DIY checks

🛠 When to call a pro

Parts that commonly fix it

Furnace pressure switch (exact OEM part for your model)

Pressure switch hose / tubing

Furnace inducer motor (exact OEM part for your model)

Carbon monoxide alarm

Related codes

Sources