Display shows F04 and heater will not fire; fan may not start.

Safety first: Turn off power and gas. Do not operate the heater with a blocked vent; risk of carbon monoxide buildup.

• Check venting: Inspect the Nirvana heater exhaust vent for obstructions such as nests, leaves, or ice. Ensure vent termination meets clearance requirements and is not blocked by landscaping or structures.
• Inspect air intake: For models with a dedicated combustion air intake, verify the intake screen is clean and unobstructed.
• Test combustion blower: With power restored (gas still off), call for heat and listen for the Nirvana combustion blower fan. If it does not start, check the blower wiring harness and connector at the control board. If the blower hums or is seized, it may need replacement.
• Check air pressure switch tubing: Power off again. Inspect the silicone tubing from the blower housing to the Nirvana air pressure switch for cracks, kinks, or water. Clear any moisture and ensure tight connections.
• Pressure switch test: With a multimeter, verify the pressure switch closes when the blower runs. If it does not close under proper airflow, replace the switch.
• Restart and test: Restore gas and power, then call for heat. If F04 persists, have a professional evaluate vent sizing and blower performance.