York furnace 8 red flashes: Lockout on recycles, flame dropouts

Eight red flashes means flame was established and then dropped out, repeatedly, until the control locked out. The furnace can light — it cannot hold the flame.

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, stored in the error code array.

What it means

York's wording here is helpfully explicit: lockout on recycles, flame dropouts. A recycle is a restart after a flame was proved and subsequently lost, as distinct from a retry where it never lit. This is a meaningfully different fault: the igniter works, the gas valve opens, a flame forms, and then something either extinguishes it or stops the control detecting it. The most common single cause is a flame sensor whose signal is falling — the flame is still burning, and the control can no longer see it well enough to keep the valve open.

Most common causes

• A flame sensor coated with oxide, giving a signal that fades within seconds of lighting.
• The flame sensor bent or shifted so it sits only partly in the flame.
• Poor grounding, which makes flame rectification unreliable.
• Low or unstable gas pressure, so the flame lights and cannot be sustained.
• Restricted combustion air, producing a flame that lifts or destabilises.
• A partly blocked flue disturbing the flame once combustion is established.
• A cracked ceramic insulator on the flame sensor.

How to diagnose it

1. Confirm this is eight and not seven flashes, since the two point at different failures.
2. Watch a start attempt if the furnace has a sight glass. Burners lighting and going out after a few seconds is the signature.
3. Note how long the flame survives — a few seconds points strongly at flame sensing; longer points at gas pressure or combustion air.
4. Check when the furnace was last serviced, since an uncleaned flame sensor is the usual explanation.

How to fix it

1. Flame sensor cleaning, grounding checks, and gas pressure testing are technician work.
2. Tell the technician that the burners do light and then go out. It rules out the igniter immediately.
3. Do not reset repeatedly. Each cycle delivers gas that briefly burns and then stops.
4. If the sensor was cleaned recently and the fault has returned, ask for grounding to be checked rather than the sensor cleaned again.

Notes

A furnace that lights, burns briefly, then shuts down and eventually locks out is the classic dirty flame sensor. It is among the most common furnace faults across every manufacturer and one of the least expensive repairs.

Related

• 7 red flashes — One hour lockout after ignition retries
• Rapid amber flashing — Low flame sense current

Sources

• Johnson Controls Unitary Products technical service letter ST-045-09 — York UTEC furnace boards, fault code tables and retrieval procedure