Oil Burner Won't Start?
Hydrostat lights all on? Reset button keeps tripping? Learn the causes, what you can safely try, and when it's time to call a professional.
Sound Familiar?
"Hydrostat has all lights on"
This indicates Aquastat/Primary Control Lockout. The burner attempted to fire but the flame sensor (cad cell) didn't detect a flame, triggering a safety lockout.
"Tried resetting but won't turn"
Multiple reset attempts = Safety Lockout. The system has detected repeated failures and is preventing further attempts to avoid a dangerous puffback condition.
Hydrostat/Aquastat Light Meanings
Understanding what your control panel is telling you
All Lights On
System in lockout mode due to failed ignition attempts
Press reset ONCE. If it trips again, call professional.
Red Light Blinking
Flame failure detected—cad cell didn't see flame
Could be dirty cad cell, no fuel, or ignition problem. Call for diagnosis.
Solid Red Light
Hard lockout—requires manual reset
Press reset button once. If repeats, don't keep pressing.
Green Light
Normal operation—system running properly
If no heat despite green light, check thermostat and aquastat settings.
No Lights
No power to burner
Check emergency switch, circuit breaker, and power cord.
Common Causes & Repair Costs
What might be wrong and how much it typically costs to fix
| Cause | DIY? | Description | Cost |
|---|---|---|---|
Out of Fuel Tank empty or fuel line frozen (outdoor tanks in winter) | Yes | Tank empty or fuel line frozen (outdoor tanks in winter) | $0 Pro: $3-5/gal fuel delivery |
Clogged Oil Filter Filter blocked by debris, restricting fuel flow to burner | Yes | Filter blocked by debris, restricting fuel flow to burner | $15-30 Pro: $150-250 |
Clogged Nozzle Nozzle blocked by carbon buildup or debris | Pro | Nozzle blocked by carbon buildup or debris | $150-300 |
Failed Ignition Electrodes Electrodes worn, cracked, or misaligned—no spark | Pro | Electrodes worn, cracked, or misaligned—no spark | $200-400 |
Faulty Primary Control Cad cell relay (Honeywell R7284, Beckett GenisysXT) locked out or failed | Pro | Cad cell relay (Honeywell R7284, Beckett GenisysXT) locked out or failed | $250-450 |
Failed Cad Cell Eye Flame detector dirty, cracked, or failed—can't see flame | Pro | Flame detector dirty, cracked, or failed—can't see flame | $150-300 |
Failed Oil Pump Pump not delivering fuel to nozzle | Pro | Pump not delivering fuel to nozzle | $400-700 |
Air in Fuel Line Air lock preventing fuel delivery (often after tank runs dry) | Pro | Air lock preventing fuel delivery (often after tank runs dry) | $150-250 |
Faulty Aquastat/Hydrostat Water temperature control failed or mis-set | Pro | Water temperature control failed or mis-set | $250-500 |
Not sure what's wrong?
Our $199 diagnostic identifies the exact issue. Fee is credited toward repairs. New customers get $100 off repairs.
Reset Button: What You Need to Know
The reset button is on your primary control (Honeywell R7284, Beckett GenisysXT, etc.)
The Right Way
- 1.Locate the RED reset button on top of the burner
- 2.Press it ONCE firmly
- 3.Wait 60 seconds for the burner to attempt ignition
- 4.If it trips again, STOP and call a professional
What NOT to Do
- ✗Don't press reset repeatedly
- ✗Don't hold the button down
- ✗Don't try more than once if it trips again
- ✗Don't ignore repeated lockouts—there's a real problem
Puffback Warning
Each reset floods the combustion chamber with unburned oil. Multiple attempts can cause a puffback—a delayed ignition explosion that can blow soot throughout your home, damage the boiler, and cause serious injury.
Frequently Asked Questions
Common questions about oil burners that won't start
Frequently Asked Questions
Get answers to common questions about our services
10 questions from our knowledge base
Still Won't Start? We Can Help.
Our NATE-certified technicians diagnose and repair oil burners every day. We carry common parts on our trucks for same-day repairs.
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