Heil furnace 6 + 1 flashes: Soft lockout — failed to light within four trials for ignition
Six flashes then one is a combination code. Six means soft lockout; the one that follows says why — the maximum retry count was exceeded after four failed attempts to light.
Applies to: International Comfort Products *9MPT and *9MPV gas furnaces using the Honeywell SV9541Q SmartValve, sold as Heil, Tempstar and Comfortmaker.
What it means
This control uses a two-part pattern for lockouts, and understanding it makes several codes readable at once. Six flashes means the control is in soft lockout. The count that follows says what put it there. Six-then-one is the maximum retry count exceeded: the furnace tried four times to establish a flame and never proved one. ICP documents that after a five minute delay the SmartValve attempts a new ignition sequence if the call for heat is still present, and that resetting the thermostat initiates a new sequence immediately. So a furnace on this code produces a burst of attempts, waits five minutes, and tries again — not intermittent operation, but a documented retry cycle.
Most common causes
- No gas reaching the burners — a closed valve, an empty propane tank, or a supply interruption.
- A failed hot surface igniter.
- A flame sensor coated with oxide, so a real flame goes undetected and each attempt is counted as a failure.
- The flame sensor bent out of the flame path.
- The SmartValve's own on/off switch in the off position.
- Low gas pressure, so no stable flame is established.
- Poor grounding, which prevents the flame rectification signal being read.
How to diagnose it
- Count the pattern properly: six flashes, a pause, then one. Reading it as seven gives a completely different fault.
- Check the gas valve's own on/off switch, which is a documented cause of ignition problems on this control.
- Check whether other gas appliances work. If none do, the problem is the gas supply.
- Watch a start attempt. Whether the burners light at all is the key split — lighting then going out points at flame sensing, never lighting points at gas or the igniter.
- Note the five-minute retry rhythm, which confirms the documented behaviour.
How to fix it
- Restore the gas supply if that is the cause, and check the manual valve is open.
- Igniter replacement, flame sensor cleaning and gas pressure testing are technician work.
- Do not reset repeatedly to force a run. Each reset delivers gas to a burner that may not light it.
- Tell the technician whether the burners light at all. That single observation splits the diagnosis in half.
Notes
Combination codes are easy to misread as a single longer count. Watching two or three full cycles before deciding is worth the extra half minute, especially here where seven flashes is a different fault entirely.
Related
- 6 + 2 flashes — Soft lockout — flame lost during run, cycling pressure switch, or blocked condensate
- 7 flashes — Soft lockout — limit trips taking longer than two minutes to reset
All codes for this manufacturer
Heil, Tempstar and Comfortmaker furnace codes — every code, with what differs between models.
What the fix costs
Four failed trials usually mean one worn part, and most often it is the igniter: $150–350 installed with the part itself $20–60 universal or $40–120 OEM, per the ignitor replacement cost guide. A flame sensor too dirty to prove the flame it lit is the cheaper finding — $80–200 to clean, per the general repair guide — and gas-supply faults are the pricier tail. One soft-lockout-specific note on timing: because this code retries every five minutes while the call for heat stands, it often presents as intermittent heat rather than no heat, which tempts people to defer the visit until the failure hardens — at which point it is an after-hours call at a $100–200 premium.
Do it yourself or call someone?
ICP documents one legitimate homeowner action: resetting the thermostat starts a new ignition sequence immediately. Used once — deliberately, to watch what happens — that is a fair test, and what you see (no glow at all, glow but no flame, flame that dies) is exactly what a technician will ask about. Used repeatedly to keep the house warm, it is re-running a failing gas-ignition sequence on a loop, which is the behaviour every lockout exists to prevent. Once is diagnosis; twice is a decision to call.
The same lockout on other control families
Every brand ends failed retries the same way, differing mainly in the recovery clock: the York UTEC board's 7 red holds for a full hour, Rheem's *RC controls flash 4 blinks after five failed attempts, and Allied's 5 flashes is its Watchguard equivalent. The ICP version is the gentlest — five minutes, then it tries again on its own. More causes and codes: igniter fault codes.
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.