Furnace fires then shuts off: what flame failure means on an oil burner
Updated 2026-06-11 · In progress — full guide arrives before the heating season
Quick answer
Your burner lights, runs 10–60 seconds, then stops: the control isn't 'seeing' stable flame and is shutting down on safety. You can check the obvious (dirty air intake, very low tank, one reset only). The actual causes — dirty cad cell, bad nozzle, weak spark, air in the fuel line — are technician territory. Never keep resetting.
What “fires then dies” actually is: flame proving 101
- The cad cell watches the flame; no stable signal within the trial window → safety shutdown. This is the system working, not failing.
The pattern tells the story
- Dies in 2–5 s vs 15–45 s vs minutes (limit trip) — three different fault families; simple table.
Homeowner-safe checks
- Tank level (stick it), filter-change recency, blocked combustion-air intake, one reset press while watching the cycle. Nothing with tools.
Why repeated resets turn this dangerous
- Each retry sprays unburned oil; puffback explained in one paragraph. One-reset rule restated.
What the tech is checking (described, not taught)
- Cad cell condition/placement, nozzle condition, electrode gap, pump pressure, air in line / lift problems, draft.
Typical repair costs
- Cad cell, nozzle, ignition parts price bands; when it’s tune-up-included.
Sources
- Honeywell R7184 (cad-cell primary) documentation
- R.W. Beckett nozzle and combustion-air guidance