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.

What does Reznor 2 Flashes mean?

Two flashes of the UT controller diagnostic LED indicate the combustion air pressure switch is reading closed while the blower is off. The control performs a safety pre-check expecting the switch to be open before the blower starts.

What does Reznor 3 Flashes mean?

Three flashes of the UT controller diagnostic LED mean the control has gone into lockout after three unsuccessful ignition trials. The burner attempted to light but flame was not established on any of the allowed trials, so the controller shuts off the gas and locks out to prevent unburned gas from accumulating.

HVAC

Reznor error codes, decoded.

Look up any Reznor fault code below. Each one is grounded in Reznor's own service documentation — the meaning, the symptoms, the causes, and the steps to clear it.

By Octavian Ghindea

Co-founder & CTO · Reviewed August 2026

Working on a Reznor unit? The complete Reznor code pack in your inbox — free.

Reznor sits in our HVAC coverage. Every page here is transcribed from the manufacturer's manuals, not scraped from forums.

What error codes does Reznor display?

Tap a code for the full breakdown — meaning, symptoms, causes, and fix steps.

1 Flash

Combustion pressure switch open with blower on

2 Flashes

Combustion pressure switch closed with blower off

3 Flashes

Lockout from three ignition trials

4 Flashes

Lockout from five flame losses

5 Flashes

Control hardware fault detected

6 Flashes

Lockout from five pressure switch losses

Get the complete Reznor error-code pack by email

Every Reznor code, meaning and first checks in one document you can save, print or forward. Free.

Common questions about Reznor equipment

Other HVAC brands we cover

AskWhiz documents error codes for these manufacturers in the same vertical:

Aermec Airquest Amana Belimo Bell & Gossett Bosch HVAC Braeburn Systems Bryant Carrier CIAT Climaveneta Comfortmaker