Reznor 2 Flashes

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. A switch that is already closed at rest signals a stuck switch or sensing fault, so the controller will not advance the ignition sequence.

Symptoms

• Diagnostic LED flashes twice, repeatedly
• Burner fails to start on a call for heat
• No heat from the radiant tube heater
• Fault is present even before the blower energizes

Common causes

• Combustion air pressure switch stuck closed
• Pressure switch contacts welded or failed
• Sensing tube routed or pinched so it holds pressure at rest
• Miswired pressure switch creating a closed signal
• Defective pressure switch

Diagnostic steps

1. 01

   Confirm the flash count

   Verify the controller LED is showing two repeating flashes rather than the single-flash or other fault patterns.

2. 02

   Check the switch state at rest

   With the blower off, confirm whether the pressure switch is reading closed when it should be open, which points to a stuck switch.

3. 03

   Inspect the sensing tube routing

   Make sure the silicone sensing tube is not pinched or trapping pressure that holds the switch closed while the blower is off.

4. 04

   Replace the pressure switch if faulty

   If the switch remains closed at rest, follow the IOM air pressure switch replacement procedure after shutting off gas and electrical supplies.

When to call a professional

Replacing the combustion air pressure switch requires disconnecting silicone sensing tubes and electrical connections inside the burner chassis, and the manual mandates turning off gas and all electrical supplies first. If the switch tests closed with the blower off and reseating the tube does not clear the fault, a qualified gas heating technician should confirm the diagnosis and complete the switch replacement to keep the heater's combustion safety interlock intact.