York furnace 6 red flashes: Pressure switch cycle lockout
Six red flashes means the pressure switch opened and closed too many times within a cycle. York marks it a one hour soft lockout, so the furnace releases itself and tries again.
Applies to: York, Luxaire and Coleman gas furnaces using the UTEC integrated furnace control boards documented in technical service letter ST-045-09. York marks this as a one hour soft lockout.
What it means
This is not a single draft-proving failure but a pattern of them. The switch is closing, proving draft, then dropping out during the cycle — repeatedly — until the control stops. That points at something different from a switch that will not close at all: a marginal or intermittent draft, where the furnace can prove draft momentarily but cannot hold it. York marking it a one hour soft lockout produces the familiar hourly heat pattern, and that timing is itself a clue that the fault is one of the soft-lockout family rather than a hard one.
Most common causes
- A partly restricted vent or intake, where draft is marginal rather than absent.
- A condensate drain that backs up during a cycle and clears between them.
- Wind at the vent termination disturbing the draft intermittently.
- An inducer weakening and unable to hold its output steadily.
- A pressure switch operating at the edge of its setpoint.
- A sensing hose partly obstructed, so pressure fluctuates.
- Ice forming progressively at the exhaust termination during a long run.
How to diagnose it
- Note that this is a repeated fault rather than a single one, pointing at an intermittent condition.
- Note the hourly pattern if present, which matches the documented soft lockout.
- Check the outside vent termination for partial restriction and note the weather.
- Check the condensate drain for slow drainage rather than complete blockage.
- Have the stored fault history replayed, since the sequence of codes around this one is informative.
How to fix it
- Clear the vent termination and condensate drain if either is partly restricted.
- The pressure switch, hose, and inducer are technician work.
- Have the vent system assessed properly if the restriction is not obvious. Marginal draft is harder to find than absent draft and produces exactly this code.
- Record when it happens — time of day, weather, how long the furnace had run. That information is something only the householder can supply and it materially helps.
Notes
Intermittent faults are the hardest to catch because the furnace usually works when the technician arrives. On these boards the stored fault history partly solves that, which is why clearing it before the visit is a real loss.