Heil, Tempstar and Comfortmaker furnace codes

ICP furnaces use two different diagnostic systems whose code tables contradict each other. Before counting flashes, find out which light you are looking at.

Also covers: Tempstar, Comfortmaker, Arcoaire, KeepRite — same manufacturer, same controls, same codes.

Heil, Tempstar and Comfortmaker are all International Comfort Products, and the model prefix tells you which brand — H for Heil, T for Tempstar, C for Comfortmaker. What it does not tell you is which diagnostic system the furnace shipped with, and that matters more. Some diagnose through a Honeywell SmartValve, where the LED is on the gas valve itself. Others diagnose through the furnace control board, read through a view port in the blower access panel. The two use different code tables for the same flash counts.

Worth knowing before you count

Five flashes means flame sensed out of sequence on a SmartValve system and a high pressure switch fault on the control board system. One is a possible gas valve problem; the other is a draft problem. Reading the wrong table could send someone to check their vent termination while gas is passing. The pages here document the SmartValve system, and each says so.

Heil, Tempstar and Comfortmaker

Which diagnostic system you have — Heil, Tempstar and Comfortmaker furnaces use two different code systems that contradict each other
Heartbeat — Normal operation — standby or a call for heat
LED off — The control is not powered
1 flash — Not used — if you are counting one flash, count again
2 flashes — Low pressure switch closed when it should be open
3 flashes — Low pressure switch still open 30 seconds after the inducer started
4 flashes — Limit switch string is open
5 flashes — Flame sensed out of sequence — flame signal still present
6 + 1 flashes — Soft lockout — failed to light within four trials for ignition
6 + 2 flashes — Soft lockout — flame lost during run, cycling pressure switch, or blocked condensate
6 + 3 flashes — Soft lockout — airflow proving circuit opened during the run
6 + 4 flashes — Soft lockout — limit circuit opened during the run
7 flashes — Soft lockout — limit trips taking longer than two minutes to reset
8 flashes — High pressure switch closed when it should be open
9 flashes — High pressure switch open when it should be closed

Other manufacturers

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.