Oil furnace troubleshooting: the complete decision chart
Updated 2026-06-11 · In progress — full guide arrives before the heating season
Quick answer
Work the list in order: thermostat set and calling → both service switches on → breaker → oil in the tank → reset button pressed ONCE. If heat isn't back after those five checks, stop — the remaining causes (fuel delivery, ignition, flame sensing) need a technician's instruments.
Before anything: two smells that end the checklist
- Strong oil smell or smoke → stop, switch off, call. Suspected CO (headache, nausea, detector) → leave the house first. This section gates the whole guide.
The five-minute homeowner checklist, in order
- Thermostat: heat mode, setpoint 5°F above room; dead batteries.
- Service switches: burner switch + the red emergency switch at the top of the stairs (the one guests mistake for a light switch).
- Breaker/fuse for the burner circuit.
- Oil level — gauge AND stick check (link tank chart).
- Reset button: ONCE only; link the reset-button guide for the full rule.
Decision chart: match your symptom
- Runs but no heat in the rooms / runs then stops / won’t start at all / starts then locks out / short-cycles — one row each linking to the symptom guides; presented as a scannable table (the chart IS the page).
What the symptom tells the tech (and why you stop here)
- Lockout = no flame proven: fuel, spark, or sensing. Describe the tech’s checks (pump pressure, electrodes, cad cell, filter) — never as how-to.
Costs: what the likely fixes run
- Service call + common-part price bands; link the tune-up and cost guides.
Prevent the 6 a.m. no-heat call
- Annual tune-up timing; don’t run the tank below an eighth; additive note.
Sources
- R.W. Beckett AFG burner manual
- Honeywell/Resideo R7184 primary control documentation
- NFPA 31: Standard for the Installation of Oil-Burning Equipment