What This Error Means

Error code 31 means the high-heat pressure switch or its relay did not close when required or reopened during operation. The exact response varies with the stage and furnace control.

Symptoms You May Notice

Furnace may remain in low heat; high heat may not engage; burners may shut off; inducer continues briefly; repeated heating attempts; code 31 flashes during startup, stage transition, or steady-state operation.

Common Causes

Blocked or undersized venting; intake restriction; condensate blockage; weak inducer performance; damaged or disconnected pressure tubing; water in tubing; faulty pressure switch or relay; high-altitude setup issue; miswired gas valve on applicable models.

Safe Troubleshooting Steps

1. Turn off furnace power. 2. Inspect accessible intake and exhaust terminations for snow, leaves, nests, or debris. 3. Look for visible water near the furnace and obvious kinks or disconnections in accessible tubing without removing components. 4. Confirm condensate tubing is not visibly kinked. 5. Do not bypass the pressure switch. 6. A technician should measure draft pressure, inspect vent sizing and condensate drainage, test the inducer and pressure switch, and verify model-specific high-altitude settings.

Parts Commonly Involved

High-heat pressure switch; pressure-switch relay; inducer motor; vent and combustion-air piping; condensate trap and tubing; integrated furnace control.

When to Call a Technician

Call a technician when code 31 repeats, the furnace cannot enter high heat, the inducer sounds abnormal, or no visible external blockage is found.

Safety Notice

A pressure switch is a combustion-safety device. Never jumper or bypass it, and discontinue furnace use if you suspect unsafe venting or combustion-gas leakage.

Manufacturer Documentation