Which diagnostic system you have, Heil furnaces: Heil, Tempstar and Comfortmaker furnaces use two different code systems that contradict each other
The same flash count means different things depending on whether your furnace diagnoses through a Honeywell SmartValve gas valve or through the furnace control board. Five flashes is a draft fault on one and a gas valve fault on the other.
Applies to: International Comfort Products gas furnaces sold as Heil, Tempstar, Comfortmaker, Arcoaire and KeepRite. Read this before counting flashes on any of them.
What it means
ICP furnaces of the same model designation were built with two different diagnostic arrangements, and their code tables genuinely contradict each other. On SmartValve systems the diagnostic LED is on the gas valve — a Honeywell SV9541Q — and the codes describe what the valve's own control has observed. On other furnaces the LED is on the furnace control board, read through a view port in the blower access panel, and the codes are a different list entirely. This is not a documentation error. They are two different components reporting on two different things, and both are correct for the furnace they came with. The consequence is that counting flashes and looking up the number is not enough — you have to know which light you are counting first.
Most common causes
- Not applicable — this page is about identifying your diagnostic system, not about a fault.
How to diagnose it
- Find where the light actually is. If the flashing LED is on the gas valve itself — a rectangular block with the gas line running into it, usually with an on/off switch on top — you have a SmartValve system and the SmartValve codes apply.
- If the light is on the control board and you are reading it through a small window in the blower access panel, you have a furnace control board system and a different table applies.
- Check the wiring label inside the furnace door. Both systems print their own code legend there, and that label is authoritative for your specific furnace in a way any general reference cannot be.
- Note the model number from the rating plate before calling anyone. On ICP furnaces the prefix tells you the brand — C for Comfortmaker, H for Heil, T for Tempstar — but not which diagnostic system it shipped with.
How to fix it
- Identify the system before acting on any code. Reading a SmartValve furnace against a control board table, or the reverse, gives a confidently wrong answer.
- The clearest example: five flashes means a high pressure switch fault on one system and flame sensed out of sequence on the other. Those are a draft problem and a gas valve problem, and they are not interchangeable.
- If you cannot tell which system you have, describe the location of the light to the technician rather than only the count. Where the LED is tells them more than the number does.
- The pages on this site under Heil, Tempstar and Comfortmaker document the SmartValve system, which is stated on each one.
Notes
This site's whole premise is that codes differ between manufacturers and between models from the same manufacturer. ICP is the clearest case of it: the same brand, the same model designation, two incompatible code tables. Anywhere that publishes one ICP table without saying which system it belongs to is giving half its readers the wrong answer.
Related
- 5 flashes — Flame sensed out of sequence — flame signal still present
- Reading a furnace fault code — How to find, count, and interpret the diagnostic light before looking anything up
All codes for this manufacturer
Heil, Tempstar and Comfortmaker furnace codes — every code, with what differs between models.
What the fix costs
The cost hiding in this page is misdiagnosis. A flash count looked up in the wrong table produces a confident wrong answer, and the expensive version of a confident wrong answer is a part: boards run $400–900 installed per the control board cost guide, and a board replaced because a valve code was read against the board table fixes nothing. Before any money moves, the $75–150 diagnostic (repair guide) should begin with which LED, which control, which table — and on this brand that is a genuine three-part question.
Do it yourself or call someone?
Identifying which system you have is safe and squarely homeowner work: establish whether the diagnostic LED you are reading sits on the gas valve body (SmartValve system) or shows through a view port in the blower access panel (board system). That single observation picks the right code table and the right pages on this site. What follows from the code — diagnosis and repair — belongs to the code's own page and, for anything touching gas or line voltage, to a technician. If a technician quotes off a code, it is fair to ask which table they used; on these furnaces that is not a pedantic question.
Other brands with the same trap
Split code systems are an industry habit, not an ICP quirk: Rheem, York and Lennox each ship contradicting tables across generations or product lines, catalogued with the rest in same code, different meanings.
What this looks like
From the outside, this usually shows up as the furnace turns over but never lights — that walkthrough covers what to check in order, and when it stops being a homeowner job.