Reznor 6 Flashes

What does Reznor 6 Flashes mean?

Six flashes of the UT controller diagnostic LED mean the control has locked out after losing the combustion pressure switch signal five times. The pressure switch closed to allow ignition but then dropped out repeatedly during operation. After the fifth loss the controller locks out and shuts off the burner, indicating an intermittent combustion airflow or pressure switch problem.

Symptoms

• Diagnostic LED flashes six times, repeatedly
• Burner starts but cuts out during the heat cycle
• Heater short-cycles before locking out
• Intermittent loss of heat output

Common causes

• Intermittent or failing combustion air pressure switch
• Partially blocked flue, vent terminal, or air inlet
• Loose, cracked, or condensate-filled sensing tube
• Weak or surging combustion blower
• Loose wiring at the pressure switch or controller

Diagnostic steps

1. 01

   Confirm the flash count

   Verify the controller LED is showing six repeating flashes, identifying a pressure-switch-loss lockout rather than a single open/closed fault.

2. 02

   Inspect the venting and air path

   Check the flue, vent terminal, and combustion air inlet for partial blockage or restriction that would cause the pressure to drop intermittently.

3. 03

   Check the sensing tube and switch

   Inspect the silicone sensing tube for cracks, looseness, or trapped condensate, and verify the pressure switch holds its signal during blower operation.

4. 04

   Reset and observe operation

   Clear the lockout and watch a full heat cycle; if the switch signal drops again, replace the pressure switch or service the blower per the IOM procedures.

When to call a professional

Intermittent pressure switch losses point to a combustion airflow or venting problem that affects safe operation, and the manual requires shutting off gas and electrical supplies before replacing the pressure switch or blower. If the heater locks out with six flashes after the venting and sensing-tube checks, have a qualified gas heating technician verify blower performance, the venting system, and switch operation before returning the unit to service.