Oil-fired burners are still a primary heat source in many regions. They feed warm air and hot water systems across the country. Most homes use pressure burners. Oil sprays into the combustion chamber at high pressure. A blower pushes it. An electric spark ignites it. The mist keeps burning.
This is a complex machine. You can’t just fix anything.
Maintenance is limited. You can handle filters. You can check the blower. Motor belts are accessible. Switches and thermostats are yours to tweak. But leave the electrodes alone. Don’t touch the oil nozzle. Air tubes, transformers, and pumps require special tools. Testing equipment is necessary. Leave those components to a professional.
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Accessing the Burner and Controls
Start by getting familiar with the unit. Remove the access panel. It covers the burner blower. Unscrew the retaining screws around the housing rim.
A metal panel on the side gives access to the air blower and filter. It’s held by hooks or retaining bolts.
Slide the panel up to clear the hooks. Or remove the bolts. Lift the panel off.
Most furnaces have switches and reset buttons. They sit on the motor. Or in a switch box outside the housing. Look for stampings. Labels say “DISCONNECT SWITCH” or “RESET.”
The stack control sensor is a safety device. It monitors burner operation. It sits in the stack. Retaining bolts hold it in place.
There’s not much you can fix. But routine maintenance stops problems before they start.
Essential Maintenance Steps
Good care eliminates many issues. Follow these steps to keep your furnace running smoothly.
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Check the chimney smoke. During the heating season, look at the exhaust. Black smoke means incomplete combustion. Fuel is wasted. Call a professional for adjustments.
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Clean the blower. Do this at the start of the heating season. Clean it again midway through.
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Clean the stack control. Remove soot about halfway through the season.
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Lubricate the motor. If the blower motor has grease or oil fittings, lubricate them midway through the season. Use cup grease or 10-weight nondetergent motor oil. Not all-purpose oil. You can find this at any hardware store.
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Clean the thermostat. Do this before each heating season.
If the furnace still fails, use a troubleshooting chart.
Routine maintenance is the only real defense against major breakdowns in oil furnaces.
For more home repair guides, check out these resources:
- Furnace Maintenance : Learn the steps to keep your furnace in prime condition.
- Major Appliance Repair : If other machines are failing, learn how to fix them here.
- Small Appliance Repair : Once you’ve handled the furnace, fixing a toaster seems easy. Find out how.
- Thermostat Maintenance : Check if the problem is actually the thermostat. Learn how to calibrate it.
The same links appear again because they’re useful.
If your furnace still isn’t working, use the handy troubleshooting chart on the next page to find a solution.
For more articles on home repair, check out the following links.
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Furnace Maintenance: Save yourself time and money by learning the steps to keep youor furnace in prime condition.
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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.
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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.
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Thermostat Maintenance: To make sure there’s actually a problem with the heating system, you may want to check the thermostat, too. Learn how to calibrate a thermostat.
Fixing a Dead Oil Furnace: Power and Fuel Checks
If your furnace is dead silent, don’t panic. Start with the basics. Oil furnace troubleshooting often starts with electricity or fuel, not complex mechanical failures.
First, check the power. Look at your main electrical panel. Did a breaker trip? Are there blown fuses? Reset them. If your furnace has a separate power switch nearby, make sure it’s turned on.
Sometimes the motor overheats and shuts off to protect itself. Wait 30 minutes for it to cool down. Then press the reset button. If it trips again immediately, stop. You have a bigger problem.
Is there fuel in the tank? Refill if needed. But if the tank is full and the furnace still won’t run, the fuel line might be blocked. This is where your next task comes in: the oil filter.
How to Clean and Replace Oil Furnace Filters
Cleaning or replacing filters is a job anyone can do. It’s often the single biggest reason an oil furnace isn’t performing at peak levels. You should change or clean the oil filter twice a year: once at the start of the heating season and again midway through.
Here is the step-by-step process for the main oil filter.
Step 1: Shut off the fuel.
Close the oil shutoff valve located between your fuel tank and the filter. This prevents a messy spill.
Step 2: Remove the filter.
Unscrew the bottom cup of the filter housing. Pull the old filter out.
Step 3: Install new or clean.
If you have a disposable filter, insert a new one of the exact same size and type. If you have a permanent filter, clean it according to the manufacturer’s instructions. Usually, this means washing it with solvent and letting it dry completely.
Step 4: Replace gaskets.
Do not reuse old gaskets. They are prone to leaking. Use new ones.
Step 5: Reassemble.
Screw the bottom of the housing back on. Open the shutoff valve slowly. Check for leaks.
If your furnace has a pump strainer, clean that too. It’s located on the pump attached to the burner/blower unit.
Tools needed:
– Wrench
– Kerosene
– Old, soft toothbrush
– Replacement pump strainer and gasket (keep a spare on hand)
Steps for the pump strainer:
1. Unbolt the cover of the pump housing where the oil line enters the burner. Lift the cover off.
2. Remove the thin gasket. Pull out the wire mesh screen (the strainer).
3. Soak the strainer in kerosene for several minutes to loosen sludge. Scrub it gently with the toothbrush.
4. Inspect it. If it’s torn or bent, replace it.
5. Place the clean strainer back. Put on a new gasket. Bolt the cover back on.
Troubleshooting Common Oil Furnace Problems
Use this guide to diagnose specific symptoms.
Furnace won’t run:
– Check power sources (breakers, switches).
– Wait 30 minutes if the motor overload tripped.
– Check for no fuel or blocked lines.
Burner won’t fire:
– Refill the tank.
– Press the reset button on the stack control. If that fails, clean the stack control.
– If your furnace has an electric-eye safety sensor, clean it. If it still doesn’t work, call a pro.
Not enough heat:
– Raise your thermostat by 5 degrees.
– Check the air filter. A dirty air filter chokes the system.
– Clean the blower assembly.
– Ensure all registers are open and not blocked by rugs or furniture.
– Check if the system is out of balance.
– Inspect the blower belt. If it’s loose or broken, adjust or replace it.
– If the burner itself is dirty, call a professional.
Furnace turns on and off repeatedly (short cycling):
– This is often a filter or lubrication issue.
– Clean or replace both the air and oil filters.
– If your motor and blower have oil ports, lubricate them.
– Clean the blower assembly again; clogs cause overheating.
– If the stack control is faulty, call a professional.
Blower won’t stop running:
– Check your thermostat setting. Switch it from “ON” to “AUTO.”
– Reset the limit switch if it’s stuck.
Furnace is noisy:
– Tighten loose access panels.
– Spray squeaking belts with fan belt dressing. Replace any worn or damaged belts.
– Adjust the blower belt tension. Too loose or too tight causes noise.
– Lubricate motor and blower ports if they have them.
– A dirty burner requires a professional to clean.
When to Call a Professional
Some issues are beyond DIY scope.
If you’ve cleaned filters, checked fuel, and reset switches but the burner is dirty, call a pro. You don’t want to tamper with the combustion chamber yourself.
If the stack control fails after you’ve cleaned it, that’s a safety component. Don’t mess with it.
If the motor overload keeps tripping after cooling down, there’s an electrical or mechanical fault inside.
Most importantly, if you smell oil or see fuel leaking after cleaning filters, shut everything down and call for help. Safety first.
How to Clean an Oil Furnace Stack Control to Restore Ignition
The stack control is a non-negotiable safety component in any oil heating system. Its job is simple but critical. It sits inside the flue pipe, or stack, and monitors the burner’s heat. If the oil ignites, the sensor stays active. If the burner fails to light, the control cuts power to the motor immediately. This prevents unburned fuel from filling your home with dangerous fumes.
Yet here is the twist. Often, the furnace shuts down not because the burner is broken, but because the stack control itself has failed. Specifically, it gets clogged.
Tools and Prep for the Job
Before you start pulling bolts, gather your supplies. You need a wrench. You need a stiff brush. Have some soapy water and a soft cloth ready. Lay down newspaper to catch the mess. Refractory cement will be necessary for resealing later.
First, verify the obvious. Check your fuel tank. If it’s empty, refill it. If fuel is present, press the reset button on the stack control. One press. Wait. Does it ignite? If yes, you got lucky. If no, the control is likely coated in soot. Clean it. Then press reset again.
If it still won’t start, stop. Call a professional. Do not keep hitting reset. You risk flooding the chamber with fuel.
The Step-by-Step Cleaning Process
Soot builds up over a heating season. It insulates the sensor. The sensor thinks the burner is cold because the soot is blocking the heat. It trips the safety. You need to remove that buildup.
1. Extract the Sensor
Use your wrench to loosen the bolts holding the control unit in the stack. The control is a cylinder with a probe inside. Pull the entire assembly out. Handle it gently. The probe is fragile.
2. Scrape and Wash
Dip your brush in soapy water. Scrub the exterior of the control housing. You are removing the carbon layer. Wipe it dry with a soft cloth. The sensor probe itself should be clean too. Ensure no soot remains on the tip. A dirty tip sends false signals.
3. Clean the Flue Pipes
This is where most people cut corners. You cannot clean the sensor and leave the pipe dirty. The pipe is the source of the soot.
Spread newspaper on the floor. Disassemble the stack sections. This means unscrewing or unbolting each pipe segment. Take each section outside or over the newspaper. Tap them firmly against the floor or a hard surface. Let the soot fall away. Remove all debris. If you leave chunks in the pipe, they will just flake off and clog the sensor again in a week.
4. Reassemble with Precision
Put the stack back together in reverse order. Align the sections carefully. They must fit snugly. Gaps cause drafts. Drafts disrupt combustion. Tighten all connections securely.
5. Reseal and Reset
Before putting the stack control back in, check the seal where the stack meets the chimney. Use refractory cement to seal any cracks. This prevents air leaks that can mess with the flame.
Insert the cleaned control back into the stack. Secure it with the bolts. Turn the power back on. Press reset. Watch it work.
What If It’s an Electric-Eye Switch?
Not all furnaces use a thermal stack control. Some have an electric-eye safety switch. It functions similarly but looks different.
If your furnace has this, you will see a photocell unit. Remove the access cover. It usually snaps on or is held by small screws. Wipe the lens clean. Soot on the lens blinds the sensor. The furnace sees “darkness” and assumes no flame.
Reattach the cover. Turn the power on. If the burner still won’t ignite, call a pro.
When to Stop DIYing
If the control or the electric-eye is excessively dirty after cleaning, there is a deeper problem. Your furnace is not burning fuel completely. The mixture of air and oil is wrong. This is inefficient. It wastes money. It creates excess soot.
You cannot fix a bad air-fuel ratio with a brush. You need a professional service person to adjust the combustion.
Caution: Do not attempt to replace the stack control or electric-eye switch yourself. These are calibrated safety devices. Improper installation can lead to carbon monoxide leaks or fire hazards.
You can set the switches to ON for operation. You just need to know where they are. If the cleaning didn’t work, and the unit is not dirty, the issue is mechanical or electrical. That requires a certified technician.
Proper maintenance saves you from emergency calls. A clean sensor means a consistent flame. It means your home stays warm without the anxiety of a sudden shutdown. Keep the stack clean. Watch the reset button. Know when to step back.
Verify Master Switches First
Some oil furnaces hide two master switches. One sits near the burner unit itself. The other might be mounted on the furnace housing or even far away in the basement. If your system won’t start, check both. They need to be in the ON position. Don’t assume the one you can see is the only one that matters.
Diagnosing the Limit Switch
The limit switch is a safety device. It lives on the furnace, just below the plenum. Its job is simple. If the plenum gets too hot, this switch shuts off the burner. It also cuts power to the blower once the temperature drops to a specific level after the burner stops.
If your blower runs all the time, something is wrong. Usually, it’s one of two things. The thermostat’s blower control is set to ON. Or the limit switch needs adjustment.
Start with the thermostat. Is the fan set to ON? Switch it to AUTO. If it was already on AUTO, the limit switch is the culprit.
How to Adjust a Limit Switch
You need to adjust the limit switch to fix the continuous blower issue. Here is the process.
- Remove the control’s cover.
- Find the toothed dial underneath.
- Ignore the side marked LIMIT. Never touch this side.
- Focus on the side marked FAN.
There are two pointers on the fan side. The blower turns on at the upper pointer setting. It shuts off at the lower pointer setting. The gap between them should be about 25 degrees.
Set the upper pointer at roughly 115 degrees Fahrenheit. Set the lower one at about 90 degrees Fahrenheit. This creates the proper differential for the fan to cycle correctly.
Adjusting the Draft Regulator
The draft regulator sits on the stack. It stays closed when the burner is off. It opens automatically when the burner turns on to let air into the chimney.
Soot buildup is a red flag. Rattling sounds inside the chimney are another. These signs mean the draft regulator needs adjustment.
Too much air in the chimney wastes heat. Too little air wastes fuel by failing to burn the oil completely.
You can tweak the airflow yourself. To increase airflow, screw the counterweight inward. To decrease airflow, turn the counterweight outward.
This is not a task for a weekend warrior. Have a professional service person adjust the draft regulator during your annual maintenance. They know exactly how much air your specific furnace needs for efficient combustion.
Burner Adjustment
Do not try to adjust the burner. Leave that to a professional service person. The settings are precise. Get them wrong and you risk inefficient burning or unsafe operation.
You now have the know-how to handle most common issues. You can check switches. You can adjust fan limits. You can spot draft problems. You won’t fix major internal failures, but you won’t be blind to the symptoms either.
For more help with home repair:
- Furnace Maintenance : Learn the steps to keep your furnace in prime condition and save money.
- Major Appliance Repair : Fix other machines in the house if the furnace isn’t the only thing failing.
- Small Appliance Repair : Once you’ve handled the furnace, a toaster or blender seems easy. Check out guides for them here.
- Thermostat Maintenance : Make sure the heating system is the problem, not the thermostat. Learn how to calibrate it.
