Oil-fired burners still heat half the country. They are the backbone of warm air and hot water systems for millions of homeowners. Most of these setups are pressure burners. That means they spray atomized oil into a combustion chamber. A blower propels the mist. An electric spark ignites it. The mixture burns continuously.
It is a complex assembly. You might think you can fix it all. You can’t.
Maintenance is where you draw the line. Simple parts are fair game. Filters. Blowers. Motor belts. Switches. The thermostat. If these components fail, you can likely handle them. But the rest? Electrodes. The oil nozzle. Air tubes. Transformers. Pumps. These require special tools. They demand testing equipment. Leave them to a professional.
You need to know your furnace. Start by locating the burner blower. Remove the access panel. Unscrew the retaining screws around the housing rim. You might find an air blower and filter behind a metal panel on the side. It usually hangs on hooks or bolts. Lift the panel up and off the hooks. Or remove the bolts. Slide it out.
Look for switches and reset buttons. They are often on the motor or in an external switch box. Labels matter here. Look for “DISCONNECT SWITCH.” Look for “RESET.” Find the stack control sensor. It is a safety device. It monitors burner operation. It sits in the stack, held by retaining bolts.
There are few quick fixes for an oil furnace. Routine maintenance prevents disasters.
Good regular maintenance can help eliminate many problems, even if you can’t fix a broken burner yourself.
Oil Furnace Maintenance Tips
If your system is still running, keep it that way. Follow these steps during the heating season.
-
Watch the chimney smoke. If it is black, the oil is not burning completely. Fuel is being wasted. This indicates a need for professional adjustment. Do not ignore black smoke.
-
Clean the blower. Do it at the start of the heating season. Do it again midway through. Dust kills efficiency.
-
Clean the stack control. Soot builds up. Remove it about midway through the season. A dirty sensor causes false readings.
-
Lubricate the motor. Only if it has grease or oil fittings. Use cup grease or 10-weight nondetergent motor oil. Do not use all-purpose oil. Hardware stores stock the right stuff.
-
Clean the thermostat. Do this before each heating season starts. A dirty thermostat gives bad readings. It makes your furnace cycle incorrectly.
If the furnace still fails, you will need a troubleshooting chart. Or you will need a pro.
Filters are the low-hanging fruit of HVAC maintenance. Change them. It’s the fix. A clogged filter chokes the system faster than you’d expect. It starves the burner. It kills efficiency. Check the chart below. See if your specific issue matches a filter-related symptom. If it does, swap it out.
Oil Furnace Troubleshooting Chart
| Problem | Possible Cause | Solution |
|---|---|---|
| Furnace won’t run | 1. No power. | Check main panel fuses or breakers. Restore circuit. |
| 2. Switch off. | Flip the separate power switch near the furnace. | |
| 3. Motor overload. | Wait 30 minutes. Press the reset button. Repeat if needed. | |
| 4. No fuel. | Check the tank. Refill if empty. | |
| 5. Fuel line blockage. | Clean the oil filter and pump strainer. Call a pro if it persists. | |
| Burner won’t fire | 1. No fuel. | Check tank. Refill if necessary. |
| 2. No ignition spark. | Press the stack control reset button. Clean the stack control if needed. Call a pro. Clean the electric-eye safety if equipped. Call a pro if no spark. | |
| Not enough heat | 1. Thermostat too low. | Raise setting by 5°. |
| 2. Air filter dirty. | Clean or replace. | |
| 3. Blower clogged. | Clean the blower assembly. | |
| 4. Registers closed/blocked. | Open all registers. Clear rugs, drapes, furniture. | |
| 5. System out of balance. | Balance the ductwork/system. | |
| 6. Blower belt loose/broken. | Adjust or replace the belt. | |
| 7. Burner dirty. | Call a professional. | |
| Furnace cycles on/off | 1. Air filter dirty. | Clean/replace. |
| 2. Oil filter dirty. | Clean/replace. | |
| 3. Motor/blower needs lube. | Oil ports? Lubricate. | |
| 4. Blower clogged. | Clean assembly. | |
| 5. Stack control faulty. | Call a professional. | |
| Blower won’t stop | 1. Control on ON. | Reset to AUTO. |
| 2. Limit switch wrong. | Reset limit switch. | |
| Furnace noisy | 1. Loose panels. | Fasten access panels. |
| 2. Stuck/worn belts. | Spray with belt dressing. Replace if damaged. | |
| 3. Belt tension wrong. | Adjust belt. | |
| 4. Motor/blower needs lube. | Lubricate if oil ports exist. | |
| 5. Burner dirty. | Call a professional. |
Filters aren’t just for air. Your oil system breathes fuel. If that fuel is dirty, the engine chokes. Clean or replace these filters twice a year. Once at the start of the heating season. Once midway through. Here is the process.
How to Clean or Replace Oil Furnace Filters
Step 1: Close the oil shutoff valve. This sits between your fuel tank and the filter housing. You need to stop the flow before you open anything up.
Step 2: Unscrew the bottom or cup of the filter housing. Remove the old filter element. It’s usually a simple twist or unbolting mechanism depending on your model.
Step 3: Check the type. If it’s disposable, toss it. Insert a new one. Must be the exact same size and type. Mismatched filters cause leaks. If your furnace has a permanent metal filter, clean it per the manufacturer’s instructions. Don’t skip this.
Step 4: Replace old gaskets. Always use new ones. Old gaskets crack. They leak. Leaks mean fire hazards and wasted fuel.
Step 5: Screw the housing back together. Tighten it. Open the shutoff valve slowly. Check for leaks immediately.
Some systems have an extra hurdle. A pump strainer. It lives on the pump attached to the burner or blower unit. You clean this when you change the oil filter. Don’t ignore it.
Tools You’ll Need for the Pump Strainer
- Wrench
- Kerosene
- Old, soft toothbrush
- Replacement pump strainer and gasket
Steps for the Pump Strainer
Step 1: Unbolt the cover of the pump housing. This is where the oil line enters the burner assembly. Lift the cover off.
Step 2: Remove the thin gasket around the rim. Locate the strainer. It’s a cylindrical or cup-shaped wire mesh screen. Pull it out.
Step 3: Soak the strainer in kerosene. Let it sit for several minutes. This loosens the sludge. Take your soft toothbrush. Scrub gently. Don’t tear the mesh.
Step 4: Inspect. If the screen is torn or badly bent, replace it. Use a new strainer of the same type. Do not try to bend it back into shape. It won’t hold.
Step 5: Set the clean (or new) strainer back into place. Put the new gasket on the rim. Bolt the cover back on. Tighten securely.
The filter is usually the culprit. But sometimes it’s the brain. The stack control. It’s a safety device. It shuts down the furnace if things go wrong. If you’ve checked filters and fuel and the unit still acts up, the stack control might be the issue. Check it next.
“Filters are the low-hanging fruit of HVAC maintenance. Change them. It’s the fix.”
For more articles on home repair, check out the following links.
- Furnace Maintenance: Save yourself time and money by learning the steps to keep your furnace in prime condition.
- Major Appliance Repair: If the furnace isn’t the only thing in the house on the fritz, you can learn how to fix other machines in this article.
- Small Appliance Repair: Once you’ve tackled the furnace, a toaster or blender seems like child’s play. Find out how to fix them here.
- Thermostat Maintenance: To make sure there’s actually a problem with your heating system, you may want to check the thermostat, too. Learn how to calibrate a thermostat.
Clearing Soot from Your Oil Furnace Stack Control
The stack control is your furnace’s watchdog. It lives inside the chimney flue, watching the burn. If the ignition fails, it cuts power to the motor. It’s a safety lock. But here’s the thing: often the furnace isn’t broken. The control is just dirty.
Before you panic or call a pro, check the fuel tank. Empty tank? Fill it. Full tank? Press the reset button on the stack control.
It won’t light? Good. You have a job to do.
Tools You’ll Actually Need
Grab these before you start. You don’t need a toolkit from hell. Just the basics.
- A wrench
- A stiff brush
- Soapy water
- A soft cloth
- Old newspaper (to catch the mess)
- Refractory cement (for sealing later)
If the burner still dies after one reset, the control is caked in soot. Clean it. Then try again. If it still fails, stop. Call a professional.
How to Clean the Stack Control
Soot builds up fast during heating season. Do this monthly. Or as soon as you see black crust forming.
Step 1: Pull the Sensor
Loosen the bolts holding the control in the stack. Pull the sensor and its housing out. Be gentle. These parts are old and brittle.
Step 2: Scrub the Soot
Dip your brush in soapy water. Scrub every inch of the control. Get into the crevices. Wipe it dry with a soft cloth. It should look clean. If it’s still black, scrub more.
Step 3: Clean the Stack Itself
Don’t just clean the control. Clean the pipe it lives in. Spread newspaper on the floor. You’re about to drop debris everywhere.
Disassemble the stack sections. Tap them firmly against the newspaper-covered floor. Soot falls out. Debris drops away. Don’t skip this. A clean control in a dirty pipe is useless.
Step 4: Reassemble the Flue
Put the stack sections back together. Reverse order of removal. Make sure they align. Tight connections prevent exhaust leaks. Leaks are bad. Dangerous, even.
Step 5: Seal and Reset
Put the stack control back in. Use refractory cement to reseal the connection to the chimney. Let it dry. Then reset the switch.
What If You Have an Electric-Eye Switch?
Some furnaces don’t use a stack control. They use an electric-eye safety switch. Same job. Different look.
If yours has one:
- Remove the access cover. It’s held by hooks or screws.
- Wipe the photocell clean. Soot blocks the sensor.
- Replace the cover.
- Turn power back on.
Does it ignite? Good. If not, call a pro.
When to Stop and Call a Pro
If the switch is especially dirty, the furnace isn’t burning fuel completely. That’s a combustion issue. Not a cleaning issue. Adjust the burners.
Don’t touch the internal calibration yourself. You can set the switches to ON. You can clean the exterior. But do not attempt to replace these controls yourself.
Find the switches. Ensure they’re in the ON position. That’s your limit.
Beyond this, you’re in expert territory.
For more fixes:
- Furnace Maintenance: Keep the system running. Save money.
- Major Appliance Repair: If other machines are failing, tackle them here.
- Small Appliance Repair: A toaster breakdown is a breeze after fixing a furnace.
- Thermostat Maintenance: Check the brain before blaming the body. Calibrate it.
The heat should return soon. Or at least, you’ll know why it didn’t.
Check Master Switches First
Oil furnaces can be tricky because some models hide two master switches. One sits right next to the burner unit. The other might be on the furnace housing or even across the room. If your heat isn’t firing, don’t guess. Check both. Make sure they are firmly in the ON position. It sounds simple. It is. But it saves hours of panic.
Limit Switch: The Safety Valve
The limit switch is your furnace’s conscience. It lives on the unit, just below the plenum. Its job is basic safety. If the plenum gets too hot, the switch cuts power to the burner. It also kills the blower when things cool down enough.
If your blower runs non-stop, you have a specific problem to solve.
Is the thermostat set to ON? If yes, flip it to AUTO. If it’s already on AUTO, the limit switch is out of whack. It needs adjusting.
Adjusting the Limit Switch
You don’t need a degree in engineering for this. Remove the control cover. Look for a toothed dial underneath. Ignore the side marked LIMIT. Touching it messes with safety cutoffs. Look at the FAN side instead.
There are two pointers on the fan side. The upper one turns the blower on. The lower one turns it off. You want a gap. Aim for about 25 degrees between the pointers. A good rule of thumb? Set the upper pointer to 115 degrees Fahrenheit. Set the lower one to 90. This keeps your air moving when it’s warm and stops it when it’s not. No more cold blasts. No more wasted electricity.
The Draft Regulator: Why Your Stack Matters
Look at the stack. You’ll see the draft regulator. It’s supposed to stay closed when the burner is off. It opens automatically when the burner kicks on. This lets air into the chimney. It’s a delicate balance.
Soot accumulation is a red flag. Rattling noises are another. Both mean the regulator needs adjustment. Too much air in the chimney wastes heat. Too little air means incomplete combustion. That wastes fuel and creates soot. You’re losing money either way.
To increase airflow, screw the counterweight inward. To decrease it, turn the counterweight outward. But here’s the catch. Don’t guess. This part should be adjusted by a professional service person during regular annual maintenance. If you’re not comfortable with it, step back.
Burner Adjustment: Leave It to the Pros
Do not try to adjust the burner yourself. Seriously. Call a professional service person. Oil furnaces are complex machines. One wrong move can lead to poor combustion or worse. You can check switches. You can tweak limits. But the burner? That’s for experts.
What You Can Fix vs. What You Can’t
You can’t fix every major problem with an oil furnace. Some things are beyond the scope of DIY. But you now have the know-how to handle most of the issues that come your way. You’ve got the basics down. The rest is maintenance and knowing when to call in help.
For more on keeping your home running smoothly, check out these guides:
- Furnace Maintenance: Save time and money by learning the steps to keep your furnace in prime condition.
- Major Appliance Repair: If the furnace isn’t the only thing in your house on the fritz, learn how to fix other machines.
- Small Appliance Repair: Once you’ve tackled the furnace, a toaster or blender seems like child’s play. Find out how to fix them.
- Thermostat Maintenance: Make sure there’s actually a problem with your heating system. Check the thermostat. Learn how to calibrate a thermostat.
