Heil furnace 6 + 2 flashes: Soft lockout — flame lost during run, cycling pressure switch, or blocked condensate
Six flashes then two means the maximum recycle count was exceeded, and the last failure was flame sense lost during the run, a cycling pressure switch, or blocked condensate.
Applies to: International Comfort Products *9MPT and *9MPV gas furnaces using the Honeywell SV9541Q SmartValve, sold as Heil, Tempstar and Comfortmaker.
What it means
A recycle is different from a retry. A retry is an attempt that never lit; a recycle is a restart after the furnace was running and something interrupted it. ICP documents that any combination of five abnormal events during a single call for heat produces a soft lockout, and the trailing count says which abnormal event happened last. Two means the final failure was one of three things grouped together: flame sense lost while running, a pressure switch cycling open and closed, or blocked condensate. All three describe a furnace that was working and stopped being able to, which is a different investigation from one that never started.
Most common causes
- A flame sensor coated with oxide, giving a signal that fades within seconds of lighting.
- A condensate drain or trap that backs up during a run and clears between cycles.
- A partly restricted vent where draft is marginal, so the pressure switch cycles rather than holding.
- Ice forming progressively at the exhaust termination during a long run.
- An inducer weakening as it warms.
- Poor grounding, which makes flame rectification unreliable.
- Low or unstable gas pressure, so the flame lights and cannot be sustained.
How to diagnose it
- Note that the furnace lit successfully before faulting. That distinguishes this from the six-plus-one retry lockout entirely.
- Note how long the furnace runs before faulting. A consistent interval points at something accumulating, such as condensate.
- Check the condensate drain for slow drainage rather than complete blockage.
- Check the outside vent termination, and note the weather — ice at the termination fits the pattern.
- Count the trailing flashes carefully. Two, three and four after the six mean different last failures.
How to fix it
- Clear a partly blocked condensate drain, which is the most common cause of a run-mode fault on condensing furnaces.
- Clear the vent termination and keep it free of snow and ice.
- Flame sensor cleaning, grounding checks and gas pressure work are technician tasks.
- Tell the technician how long the furnace runs before faulting. That observation distinguishes several of the causes and only the householder can supply it.
Notes
The five-abnormal-events rule is worth knowing: the furnace tolerates a few interruptions within one call for heat before locking out, so this code means a pattern rather than a single event.
Related
- 6 + 3 flashes — Soft lockout — airflow proving circuit opened during the run
- 6 + 1 flashes — Soft lockout — failed to light within four trials for ignition
All codes for this manufacturer
Heil, Tempstar and Comfortmaker furnace codes — every code, with what differs between models.
What the fix costs
Three grouped causes, three price bands, all modest: a flame sensor that loses the flame mid-run cleans up for $80–200; a cycling pressure switch prices at $150–400, with the switch often innocent because the cycling draft is the real fault; and blocked condensate is typically a clearing job inside an ordinary service call, $75–150 diagnostic included, per the furnace repair cost guide. This is a lockout that rarely ends in an expensive part. What it does demand is an actual diagnosis, because the three causes leave different evidence and share nothing but the code.
Do it yourself or call someone?
Safe looking, no touching: water pooled around a condensing furnace or a visibly kinked drain line points at the condensate branch of this code — the site's leaking water walkthrough covers what that means — and is worth reporting when you book. Weather is worth noting too; a pressure switch that cycles in high wind or hard freezes narrows the search. The trap, the sensing hoses, and the flame sensor are all inside the cabinet and all technician work. And a furnace that keeps recycling into lockout should not be nursed along on thermostat resets — five abnormal events per heat demand is the control telling you it is losing ground.
The same accounting on another control
Allied's -02 control runs the same five-strikes bookkeeping from the other direction: its 10 flashes is specifically a pressure switch opening five times in one heat demand, where ICP pools any five abnormal events and reports the last one. Related cross-brand lists: pressure switch codes and flame sensor codes.
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.
This can also show up as the pilot light will not stay lit — that page walks through thermocouple, draft and gas causes in order.