Oil heat still runs a lot of homes. It’s old school, sure. But pressure burners are efficient when they’re tuned right. The system pumps oil into a combustion chamber under high pressure. A blower pushes it in. An electric spark lights it up. The mist burns. That’s the gist.
The machine itself is complicated. Don’t try to fix the guts. The electrodes, the nozzle, the air tubes, the transformer, the pump—leave those to a pro. You need special tools for that stuff. But you can handle the rest. Filters. The blower. Motor belts. Switches. The thermostat. These are your domain.
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Know Your Furnace Parts
Before you touch anything, know what you’re looking at. Pull the access panel off the burner blower. Unscrew the retaining screws around the rim. On the side, there’s a metal panel for the air blower and filter. It’s held by hooks or bolts. Slide it up or take the bolts out. Lift it off.
Look for the switches. They’re usually on the motor or in a box outside the casing. Labels help. You’ll see DISCONNECT SWITCH. RESET. Stuff like that. Then there’s the stack control sensor. It’s a safety device. It sits in the stack. Bolts hold it in place. It watches the burner. If it sees trouble, it shuts things down.
Oil Furnace Maintenance Tips
You can’t fix much on these units. But you can keep them running. Routine care stops problems before they start.
Check the chimney smoke during the heating season. Black smoke? Bad. That means incomplete combustion. You’re wasting fuel. Call a pro to adjust the burner.
Clean the blower. Do it at the start of the season. Do it again halfway through.
Soot builds up on the stack control. Clean that off midway through the season too.
Lubricate the blower motor if it has fittings. Use cup grease or 10-weight nondetergent motor oil. Not all-purpose oil. Hardware stores carry it. Do this mid-season.
Clean the thermostat before each season starts. Dust messes with sensors.
Troubleshooting Oil Furnaces and Oil Heaters
Sometimes it just stops working. Before you call someone, check the basics. A dirty filter is the usual suspect. It kills performance fast.
Here is how to diagnose common issues.
Furnace won’t run
– No power. Check fuses or circuit breakers at the main panel. Reset them.
– Switch is off. Turn on the power switch near the furnace.
– Motor overload. Wait 30 minutes. Press the reset button. Try again if needed.
– No fuel. Check the tank. Refill it.
– Fuel line blockage. Clean the oil filter and pump strainer. If it still won’t run, call a pro.
Burner won’t fire
– No fuel. Check the tank.
– No ignition spark. Press the reset button on the stack control. Clean the control if needed. If there’s an electric-eye safety sensor, clean it. If it still won’t fire, call a pro.
Not enough heat
– Thermostat set too low. Raise it 5 degrees.
– Air filter dirty. Clean or replace it.
– Blower clogged. Clean the blower assembly.
– Registers blocked. Open them up. Move rugs and furniture away from vents.
– System out of balance. Rebalance the system.
– Blower belt loose or broken. Adjust or replace the belt.
– Burner dirty. Call a pro.
Furnace turns on and off repeatedly
– Air filter dirty. Clean or replace it.
– Oil filter dirty. Clean or replace it.
– Motor or blower needs lubrication. Oil the ports if your model has them.
– Blower clogged. Clean the assembly.
– Stack control faulty. Call a pro.
Blower won’t run
– Blower control issues. Check the wiring or controls. If you aren’t comfortable with electrical work, stop and call a technician.
Most of this is simple. The rest isn’t. Know your limits. If it involves high voltage or fuel lines, step back. The pros have the gear for that. You have the screwdriver and the filter. Use them.
Fixing a noisy oil furnace
Is your furnace rattling? Squeaking? Making sounds that shouldn’t be there?
Usually, it’s simple. Loose access panels. Just mount them back correctly. Fasten them down.
Belts can be the culprit. If they’re sticking or worn, spray them with fan belt dressing. If they’re damaged, replace them. A belt that’s too loose or too tight needs adjustment. Check the tension.
Motor and blower might need oil. Look for oil ports. Lubricate if present.
Dirty burner? That’s a pro job. Call a technician.
How to clean and replace oil furnace filters
You should change or clean the oil filter twice a year. Once at the start of the heating season. Once midway through.
Here is the process.
- Close the oil shutoff valve between the fuel tank and filter.
- Unscrew the bottom cup of the filter housing. Remove the filter.
- If it’s disposable, insert a new one of the same size and type. If it’s permanent, clean it per the manufacturer’s instructions.
- Replace old filter gaskets with new ones.
- Screw the housing bottom back in. Open the oil shutoff valve.
Some units have a pump strainer. It’s on the pump attached to the burner/blower unit. Clean this when you handle the filter.
You’ll need:
– Wrench
– Kerosene
– Old soft toothbrush
– Replacement pump strainer and gasket
Unbolt the pump housing cover where the oil line enters. Lift it off. Remove the thin gasket around the rim. Find the strainer. It’s a cylindrical or cup-shaped wire mesh screen.
Soak the strainer in kerosene for several minutes. This loosens built-up sludge. Carefully scrub it with the old toothbrush.
Inspect it. Torn? Badly bent? Replace it with a new strainer of the same type.
Set the strainer back on the pump. Place a new gasket on the rim. Bolt the cover back on.
How to clean the oil furnace stack control
Sometimes the issue isn’t the filter. It’s the stack control. This safety device sits in the stack. It monitors the oil burner. If the burner fails to ignite, the stack control shuts off the motor.
Often, the furnace shuts down because the stack control malfunctions, not the burner.
If the burner won’t ignite, check the fuel tank. Refill if needed. If the tank is full, press the reset button on the stack control.
If it doesn’t ignite after one press, clean the control. Then press reset again. Still no luck? Call a professional.
The stack control gets coated with soot over the season. Clean it monthly or as soon as you see soot.
You’ll need:
– Wrench
– Brush
– Soapy water
– Soft cloth
– Newspaper
– Refractory cement
Remove the bolts holding the control in the stack. Pull out the sensor and housing. Dip a brush in soapy water. Scrub all soot off the control. Wipe it dry with a soft cloth.
Before putting the control back, clean the stack. Spread newspaper on the floor. Disassemble the stack sections. Tap them firmly on the newspaper to remove soot and debris.
Reassemble the sections in reverse order. Align them properly. Connect them firmly.
Reposition the stack control in the stack. Reseal the connection to the chimney with refractory cement.
Some oil furnaces use an electric-eye safety switch instead. It does the same job. If yours has this, remove the access cover over the photocell. It’s held by hooks or retaining screws. Wipe the cover clean to remove soot. Reassemble the switch. Replace the cover. Turn the power back on.
If the burner still won’t ignite, call a professional service person.
How to adjust oil furnace limit switches and draft regulators
Safety first. If the stack control or electric-eye switch is caked in soot, your furnace might not burn fuel completely. That’s a professional job. Do not touch these controls yourself.
You can check the master switches. They need to be ON for the system to work.
Locate the master switches
Some oil furnaces have two. One sits near the burner unit. The other might be on the furnace housing or further away. Flip both to ON.
How to fix a constantly running furnace blower
The limit switch lives just below the plenum. It’s a safety device. If the plenum overheats, it kills the burner. It also shuts off the blower once the heat drops after the burner stops.
Is your blower running non-stop?
Check the thermostat first. Is the fan setting on ON? Switch it to AUTO. If it’s already on AUTO, the limit switch needs adjustment.
Adjusting the limit switch
1. Remove the control cover.
2. Find the toothed dial underneath.
3. Ignore the side marked LIMIT.
4. Look at the side marked FAN.
There are two pointers here. The blower starts at the upper pointer and stops at the lower one. They need to be about 25 degrees apart. Set the upper pointer to roughly 115 degrees Fahrenheit. Set the lower one to 90 degrees Fahrenheit.
Why your chimney might be wasting heat
The draft regulator is 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.
Hear rattling? See soot buildup? The regulator needs tweaking.
Too much air wastes heat. Too little air wastes fuel because it doesn’t burn completely.
Adjusting airflow
* To increase airflow: Screw the counterweight inward.
* To decrease airflow: Turn the counterweight outward.
This should be part of annual maintenance by a pro.
Burner adjustment?
Leave it alone. Call a service person. Do not try to adjust the burner of an oil furnace yourself.
You can’t fix major issues. But you can handle the small stuff. That’s the goal.
