Heil furnace 5 flashes: Flame sensed out of sequence — flame signal still present
Five flashes means the control is still detecting a flame when there should not be one. Either gas is burning when it should not be, or the sensing circuit is reporting a flame that is not there.
Applies to: International Comfort Products *9MPT and *9MPV gas furnaces using the Honeywell SV9541Q SmartValve, sold as Heil, Tempstar and Comfortmaker. On the other ICP diagnostic system, five flashes means a high pressure switch fault instead — confirm which light you are reading.
What it means
ICP's wording is precise: flame sensed out of sequence, flame signal still present. The control watches the flame sensor continuously, not only during the burn, and detecting flame outside the expected part of the cycle produces this code. It is treated seriously because one of the two possible causes is a gas valve that is not fully closing — gas entering the combustion chamber outside a controlled sequence. The other is electrical: a short in the flame sensing circuit produces a signal the control cannot distinguish from a real flame. Since it cannot tell them apart, it assumes the dangerous one, which is correct behaviour for a control managing a gas appliance.
Most common causes
- A gas valve leaking through or not closing fully.
- A slow-closing gas valve, where flame lingers after the cycle ends.
- A short to ground in the flame sensor wiring or at the sensor.
- A chafed or damaged sensor wire touching the cabinet.
- Residual flame on a burner after the main flame is cut.
- A failed SmartValve control misreading the flame signal.
How to diagnose it
- Note any smell of gas and act on it immediately rather than continuing to diagnose.
- Do not open the burner compartment while the furnace is powered. There is no safe homeowner check for this fault.
- Confirm you are reading the gas valve LED. On the ICP control board system, five flashes means a high pressure switch fault, which is an entirely different and less urgent problem.
- Note whether the inducer runs continuously without the furnace heating, which can accompany this condition.
How to fix it
- If you smell gas: leave the building, operate no electrical switches, and call your gas utility's emergency line or the fire service from outside. Do not go back in to investigate.
- With no gas smell, turn the furnace off at its service switch and leave it off until a licensed technician has seen it.
- This fault is entirely technician work. It involves the gas valve and the flame-sensing circuit — the two parts of a furnace a homeowner should never work on.
- Do not reset repeatedly to see whether it clears. If a valve is passing gas, each reset is another opportunity for it to accumulate.
Notes
This is the code where the two ICP diagnostic systems diverge most dangerously. Five flashes on the control board system is a draft problem worth investigating at leisure. Five flashes here is a possible gas valve fault. Reading the wrong table could send someone to check their vent termination while gas is passing.
Related
- Which diagnostic system you have — Heil, Tempstar and Comfortmaker furnaces use two different code systems that contradict each other
- 6 + 2 flashes — Soft lockout — flame lost during run, cycling pressure switch, or blocked condensate
All codes for this manufacturer
Heil, Tempstar and Comfortmaker furnace codes — every code, with what differs between models.
Not sure this is your brand?
The same count means something else on other furnaces. What 5 flashes means on every brand puts them side by side.
What the fix costs
The two possible causes sit at opposite ends of the price sheet. A shorted flame-sense circuit is wiring work — findable in a normal diagnostic visit ($75–150, usually credited) and often fixed within it. A gas valve that is not closing fully is the serious end: $300–900 per the furnace repair cost guide, which marks the gas valve as never a DIY part. On this code, do not price-shop your way into delay. The control is reporting possible uncommanded gas flow, and the correct spend is whatever the prompt visit costs.
Do it yourself or call someone?
Call — this is one of the few SmartValve codes with no homeowner-checks preamble. The control cannot distinguish a wiring short from a leaking valve, so it assumes the dangerous one, and you should too: shut the furnace off at the service switch and book the visit. If there is any smell of gas, leave the building and call the gas utility from outside before anything else. What not to do is equally specific: no power-cycling to see whether the code clears, and no running the furnace one more night — a valve passing gas outside its sequence does not improve with use.
The same fault on other control families
Flame sensed when none should exist is coded almost everywhere: Carrier's code 22, Goodman's 5 flashes, the 1 red on York UTEC boards, and Lennox's alert 241 all describe the same out-of-sequence flame signal — 22 codes across 11 families, gathered on flame sensor codes. The Goodman GMEC96 table adds a valve-side variant, gas flow detected out of step with the call for heat, as 10 red.
What this looks like
From the outside, this usually shows up as the burner lights and then drops out a few seconds later — that walkthrough covers what to check in order, and when it stops being a homeowner job.