Keep the furnace off. Do not reset a rollout switch. If you smell gas or a carbon-monoxide alarm sounds, leave the building and contact emergency services or the gas utility.
What does Day & Night code 4 Flash mean?
Day & Night furnace code 4 Flash means the limit or flame-rollout circuit is open on the supported control family. Confirm the model number and diagnostic chart inside the furnace door before replacing parts.
What causes Day & Night code 4 Flash?
- A blocked flue or combustion-air path
- A burner or gas-pressure problem
- A damaged or restricted heat exchanger
Can I troubleshoot Day & Night code 4 Flash?
Keep the furnace off. Do not reset a rollout switch. If you smell gas or a carbon-monoxide alarm sounds, leave the building and contact emergency services or the gas utility.
How much does Day & Night code 4 Flash cost to fix?
A heat exchanger replacement typically costs between $500 and $3,500 nationally.
When should I call a technician?
Leave the furnace off and call a licensed technician for a combustion-safety inspection.
Symptoms this code causes
Sources and model scope
Fault codes vary by model and control board. Confirm the diagnostic chart inside your furnace panel or the official manual before acting.
Scope used here: ICP control boards covered by document 44001202103 and using its 2–10 flash table.
- International Comfort Products: Furnace Control Board Diagnostic Codes
44001202103 · ICP furnace control boards covered by document 44001202103; confirm the control-board label and door chart.
Compiled by Warmlo Editorial · Reviewed August 2026
This is general information, not professional advice. Gas, electrical, and combustion repairs can be dangerous — when in doubt, call a licensed technician.