Updated December 27, 2023

The oil pump is one of the most important parts of an oil furnace. The pump works to supply oil to the oil burner motor, which then sprays out a high-pressure stream of oil and ignites it so that the furnace runs and produces heat. Depending on where your furnace is located in relation to your oil tank, the pump may also be responsible for drawing oil from the tank. However, the oil may also flow naturally to the pump due to gravity.

If the oil pump fails, your furnace won’t ever light since no oil will flow to the burner motor. There are also numerous other issues that will prevent your furnace from lighting, such as a clogged oil filter or nozzle, a worn-out burner motor, or simply because your oil tank is empty. As a result, diagnosing whether your furnace won’t light due to a bad oil pump or some other issue can be quite tricky and will usually require the help of a furnace technician. However, there are a few clues that can help you to know if your oil pump is bad. here are what steps you should take and what to look for if your oil furnace won’t light.

Read on to learn more about this common furnace repair in Gilbert, AZ.

Make Sure Your HVAC System Has Power

If your furnace won’t turn on, you’ll want to check your electrical panel to make sure the circuit breaker isn’t tripped. If the breaker is tripped, shut off your heating at the thermostat and then reset the breaker. You’ll then want to check to make sure there isn’t some other electrical issue preventing your system from running. The easiest way to do this is to switch the fan setting on the thermostat from Auto to On. The fan should then come on immediately.

If the fan doesn’t come on, there is a high chance the problem lies with your HVAC system’s electrical wiring. However, there is also a chance that the thermostat itself is the problem as it could be faulty or even simply have dead batteries.

Check That Your Oil Tank Isn’t Empty

After checking that the system has power, you’ll also want to make sure that your oil tank is empty. As long as you regularly monitor the oil level in the tank and have a rough idea of how much oil your furnace normally burns in a day, you normally shouldn’t have to worry about running out. However, extremely cold or windy weather can drastically increase the amount of oil the furnace burns in a day so there is always a chance that your oil tank could be empty.

Reset the Furnace

If an oil furnace ever turns on and fails to light for any reason, the flame failure safety switch will trigger and shut the unit down to prevent the burner motor and other components from possibly being damaged. When this happens, it essentially locks out the furnace so that it can’t run until you press the rest button. As such, the next thing you will need to do after ensuring the furnace has power is press the red button to reset the furnace, which is usually located on a metal box that sits on top of the oil pump.

The way that oil furnaces work is they use a light-sensing cad cell to ensure the burner is lit. This is similar to the cad cell that automatically turns on outdoor lights once the sun goes down.

The cad cell can fail, which will cause the unit to shut down soon after lighting and trip the flame failure safety switch. However, if your furnace doesn’t light at all, then the problem is most likely not related to the cad cell.

Check to See If the Oil Burner Motor Switch Is Tripped

Some oil furnaces have a second reset switch located on the side of the oil burner motor itself. This is the thermal overload switch that is designed to trigger if the burner motor overheats or has certain other issues. You can check to see if this switch is triggered simply by pressing it in as the switch will make an audible click when it resets. As soon as you reset the burner motor, you should hear it come on. If the motor doesn’t come on or starts making lots of loud or unusual noises, you can be fairly certain that it needs to be replaced as burner motors are generally not designed to be serviceable.

If you do hear the motor come on and the furnace doesn’t light, the flame failure safety switch will then trigger again. If the switch triggers again, you should never reset the furnace a second time and instead immediately call to schedule an inspection. A furnace that continually resets due to a bad cad cell isn’t that big of an issue, but many of the other problems that can cause it to reset can be quite serious and could do major damage if you continue trying to run the unit.

Listen to Hear If the Oil Pump Starts

When your furnace tries to turn on, you should hear both the oil pump and the burner motor start. The oil pump isn’t all that loud, but you should still be able to hear if it is running. If the oil pump doesn’t run, it is most likely bad and will need to be repaired or you’ll need a furnace replacement. Loud humming, buzzing or other unusual sounds coming from the pump can also be a sign that it is wearing out and you need to have it replaced.

If you do hear the oil pump run and your furnace doesn’t light, you’re left with only one option and that is to have a technician inspect your furnace and other HVAC components. Even if the oil pump runs, it may still be bad and no longer able to provide enough oil to the burner. The filter or screen in the oil pump could also be clogged to the point where almost no oil can flow to the burner, and this can put extra strain on the pump and cause it to fail.

The technician will also usually bleed the system as sometimes air can get inside the line and create a vacuum that prevents the oil from flowing. They will also check that the line running from your oil tank to the oil pump isn’t leaking as this can make it impossible for the pump to produce enough pressure to draw oil in and supply it to the burner. The technician may also clean or replace the oil nozzle since it often becomes clogged, and then they will need to check to make sure that the burner motor is spraying the oil out at the correct pressure.

Contact A/C Doctors Today

If you have any issues with a furnace, heat pump, air conditioner or any other HVAC unit, you can trust the team at A/C Doctors for all of your HVAC repair needs. We repair and service all makes and models of heating and cooling equipment, and we also specialize in ventilation, indoor air quality and HVAC installation. We serve both residential and commercial customers in Gilbert and throughout the Phoenix area so contact us today to get the professional service and support you need.

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