Reznor 1 Flash

What does Reznor 1 Flash mean?

On Reznor radiant tube heaters with the UT burner controller, a single flash of the diagnostic LED means the combustion air pressure switch is reading open while the blower is running. The control expects the switch to close once the blower proves combustion airflow, so an open switch during blower operation blocks the ignition sequence and prevents the burner from firing.

Symptoms

• Diagnostic LED on the burner controller flashes once, repeatedly
• Blower runs but the main burner never ignites
• No heat output from the radiant tube heater
• Unit cycles on a call for heat without establishing flame

Common causes

• Combustion air pressure switch stuck or failed open
• Blocked, disconnected, or cracked pressure switch sensing tube
• Obstructed flue, vent terminal, or combustion air inlet
• Weak or failing combustion blower not generating enough pressure
• Loose or damaged wiring between the pressure switch and controller

Diagnostic steps

1. 01

   Confirm the flash count

   Observe the controller LED and verify it is a single repeating flash, distinguishing it from the steady-on (control OK) and other multi-flash fault states.

2. 02

   Inspect the sensing tube

   Check the silicone tube to the combustion pressure switch for kinks, cracks, blockage, or disconnection and reseat it securely.

3. 03

   Verify the blower and air path

   Confirm the combustion blower runs on a call for heat and check that the flue, vent terminal, and combustion air inlet are clear of obstruction.

4. 04

   Check the pressure switch and wiring

   Inspect the pressure switch wiring connections for damage; the IOM directs replacing the air pressure switch when it does not respond correctly.

When to call a professional

Diagnosing and replacing the combustion pressure switch, blower, or controller involves live gas and electrical components, and the manual requires turning off the gas and all electrical supplies before any repair work. If the LED still flashes once after checking the sensing tube and air path, have a qualified gas heating technician verify switch operation, blower performance, and the venting system before returning the heater to service.