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.

How these furnaces signal codes

Finding the light is the diagnosis's first step, because where it is tells you which table applies. On SmartValve furnaces the LED is on the gas valve itself — a Honeywell SV9541Q, the rectangular block with the gas line running into it and an on/off switch on top — and the codes describe what the valve's own control has observed. On the other arrangement the LED is on the furnace control board, read through a view port in the blower access panel, flashing a different code list entirely. The SmartValve system also uses two-part codes: six flashes, a pause, then a second count, so 6+1 and 6+4 are different faults rather than miscounts. Two further details worth knowing: the wiring label inside the furnace door prints the code legend for your specific furnace and is authoritative over any general table, and stored ICP codes clear after 72 hours — so a code from last week's failure is probably already gone, unlike on brands that hold their history indefinitely.

The codes people look up most

The 6+1 soft lockout — failed to light within four trials — is the classic no-heat morning code. Three flashes means the low pressure switch was still open 30 seconds after the inducer started, a draft and venting question. Four flashes is the open limit string, usually an airflow problem upstream of the switch. Five flashes, flame sensed out of sequence, is the one to treat most seriously on this system: the valve control is reporting flame when there should be none, which is gas valve territory and not a reset-and-retry situation. And 6+2 — flame lost during the run — carries a cause the others do not: a blocked condensate drain, common on these condensing furnaces.

Which models these pages cover

These pages document the SmartValve diagnostic codes from the International Comfort Products *9MPT and *9MPV installation instructions. ICP sells the same furnaces as Heil, Tempstar, Comfortmaker, Arcoaire and KeepRite, and the model prefix names the brand — H for Heil, T for Tempstar, C for Comfortmaker — without revealing which diagnostic system the furnace shipped with. That is why the first check is the location of the LED, not the model number. If your light is on the control board rather than the gas valve, these tables do not apply to it.

What the common fixes cost

Because this diagnostic system lives on the gas valve, its codes point at valve faults more often than other brands' do — and a failed gas valve runs $300–900 installed and is never a DIY part. The 6+1 ignition lockout usually ends cheaper: flame sensor cleaning at $80–200, or a hot surface igniter at $150–350 installed. Pressure switch codes (three and eight flashes) run $150–400 with the venting checked first, and limit-related codes (four flashes, 6+4, seven flashes) are $150–350 plus finding the airflow or overheating cause. A $75–150 diagnostic visit, often credited against the repair, is the sensible move whenever the SmartValve is implicating itself.

Heil, Tempstar and Comfortmaker

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
Heartbeat — Normal operation — standby or a call for heat
LED off — The control is not powered
Which diagnostic system you have — Heil, Tempstar and Comfortmaker furnaces use two different code systems that contradict each other

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.