Rheem Furnace Won’t Start – What Could Be Wrong?

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A furnace helps keep your home as comfortable as possible, especially during winter when indoor temperatures fall below 60 °F, since it provides an efficient heating system for the home. But like any other appliance, the furnace may malfunction from time to time. What could be wrong when your Rheem furnace will not start? We talked to the technical experts, and this is what they have to say.

Identifying why your Rheem furnace is not starting will enable you to troubleshoot and restore the unit's functionality. Your Rheem furnace may not start due to any of the following:

  • The circuit breaker has tripped.
  • The thermostat is faulty.
  • The furnace is not getting sufficient airflow.
  • The pilot light of a gas furnace has gone out.
  • The blower motor is faulty.
  • The ignition switch is defective.

A Rheem furnace is composed of different components that may cause the appliance not to start if they malfunction. Dive in as we will discuss at length reasons why your Rheem furnace won't start. We will also discuss ways to troubleshoot and reset the furnace.

technician repairing Gas Furnace using digital tablet. Rheem Furnace Won't Start - What Could Be Wrong

Why won't your Rheem furnace start?

A Rheem furnace re-heats your home very quickly, speedily providing comfort to your home. However, the furnace may fail to start making the cold winter air unbearable. When this happens, investigate for the following.

house electrical circuit breaker close up photo

Tripped circuit breaker

The circuit breaker protects the wires that supply power to the furnace from an overload such as shorted heating element or motor. A flipped circuit breaker is a warning sign that something is wrong with your home's electrical system.

Rather than resetting the circuit breaker each time it trips, it is advisable to investigate why it keeps tripping. The breaker may trip due to the following:

  • A clogged air filter may cause insufficient airflow in the furnace. The inadequate draft strains the blower, thus triggering a tripped circuit breaker.
  • Blocked air vents may cause a high air pressure inside the ventilation system. Congested air vents add more pressure on the blower, overloading the electrical circuit.
  • The motor is faulty. Dilapidated wiring in the motor can lead to short-circuiting and arcing, triggering the breaker to trip.
  • Ventilation leaks cause the furnace to overwork to compensate for the heat lost through cracks. The furnace's circuit breaker may trip due to being overloaded.
  • The electrical board or the circuit breaker is faulty.

Woman regulating heating temperature with a modern wireless thermostat installed on the white wall at home. Cropped view focused on hand

Faulty thermostat

The thermostat communicates your home's heating and cooling needs to the furnace. It determines when and how much heat is distributed.

The thermostat may malfunction due to the following:

  • The thermostat is not receiving power either because the power switch is off or the batteries are drained.
  • Loose wiring or corroded wires in the thermostat result in poor communication in the furnace. Consequently, the furnace does not respond appropriately to temperature changes.
  • It accumulated dirt and debris that inhibited the thermostat's sensitivity.
  • A thermostat with a mercury bulb is not mounted level to the wall. The thermostat must be level to the wall to function efficiently.
  • The thermostat's capabilities are not compatible with the furnace's requirements. The mismatch may cause the thermostat to fail.

A Rheem furnace may also fail to start if the thermostat is set to low temperatures even though it may be in good working condition. It is advisable to check whether the thermostat settings are appropriate for your home.

Insufficient airflow

Combustion requires oxygen. In the absence of adequate circulation, the furnace will not start.

Restricted airflow may result from:

  • Loose insulation or other loose objects that obstruct the ducts.
  • The ductwork can collapse due to pressure imbalances, heavy impact, or natural wear and tear, inhibiting airflow.
  • Dirt in the air handler and filters.
  • Corroded ducts that result in the air not reaching the vents where it can be useful.

When airflow is restricted, the furnace is insufficient. Depending on the type of motor installed, the blower motor compensates by either slowing down or using more electricity to keep up. Moreover, the furnace may break down frequently as it overworks to compensate for the heating deficiencies.

The pilot light is off

The pilot light is found on gas-fuelled furnaces. It ignites the gas to switch on the furnace and provides heat. Therefore, your Rheem furnace will not start if the pilot light is off.

The pilot light may go out due to poor ventilation. However, it may also go off due to a faulty thermocouple. The thermocouple keeps gas from leaking into your home when the pilot light is off. If the thermocouple is defective, it will shut down the gas valve in the furnace. Consequently, the furnace will not start.

Faulty motor

The blower motor redirects conditioned air from the furnace, through the ducts, and into the home. As previously mentioned, a strain on the blower motor can cause it to malfunction, leading to circuit breaker flipping. Thus, the furnace will not start.

The motor may malfunction due to:

  • A broken blower motor belt thus prevents the fan from spinning.
  • Poor maintenance of the blower whereby it is not lubricated. This may result in screeching noises when the fan is in use.
  • Loose motor mounts that cause banging noises during operation.

Defective ignition switch

The ignition switch communicates to the furnace when it is safe to light up. When it is faulty, it does not sense the flame, so it does not communicate that it is secure to release the gas supply.

The ignition switch may malfunction if it has cracks or becomes dirty and is therefore unable to sense the flame. Thus, the furnace will not light up.

handyman repairman conducting residential HVAC repair

How to troubleshoot a Rheem furnace

You do not have to buy a new furnace just because it will not start. Troubleshooting your Rheem furnace will help you resolve some common issues. However, it is advisable to engage a professional if the furnace does not start due to electrical or mechanical faults.

Check the circuit breaker

Typically, the circuit breakers are located with your main power panel. Manually inspect whether the breakers are in the 'ON' position. If the circuit breaker is set at 'ON,' but the furnace will not start, you will need to investigate an electrical problem.

However, if the circuit breaker has tripped, switch it back to 'ON.'

It is prudent to observe how often the circuit breaker flips as this would enable you to arrest problems with the furnace before they balloon and become too expensive to repair.

Inspect the thermostat

Observe the thermostat settings and ensure that it is set to a higher level than the ambient temperature. Further, replace the thermostat batteries and observe whether the furnace starts.

How to test the thermostat

To test whether the thermostat is sending signals to the furnace, slowly raise the thermostat heat settings and listen for a click sound in the thermostat and the furnace. If the furnace does not sound, the thermostat is faulty and should be replaced.

You can also test the thermostat by twisting the ends of the wires beneath the screws together. Ensure that the circuit breaker is on. If the furnace lights, the thermostat is faulty.

However, if the furnace does not come on, the thermostat does not need to be replaced. Instead, keep troubleshooting to identify why the furnace will not start.

It is essential to ask a professional to replace the defective thermostat, especially where electrical wiring is involved.

Increase airflow

Inspect the ductwork for leaks and wear and tear. It is recommended to use aluminum duct tape to seal the gaps in the ductwork. Additionally, clean the ductwork by removing any obstructions that hinder proper air circulation.

You can also improve the airflow by cleaning or replacing the clogged air filters. Cleaning the filters also enriches indoor air quality.

Check the pilot light

Check for a little flame in the front panel of the furnace. If you cannot spot the flame, it is probably off. Further, observe the color of the flame to determine whether the furnace is working as expected. If the flame is any color besides blue, clean the unit as the flame may indicate dirt or incomplete combustion.

Follow the manufacturer's instructions to re-light the pilot light.

Replace faulty parts

It is not advisable to replace faulty parts such as a motor and ignition switch unless you are knowledgeable about electricity. If you carry out the above and the furnace still will not come on, call the professionals and ask them to look at it for you.

How do you reset a Rheem Furnace?

Most Rheem furnaces have a reset button that shuts the furnace before the circuit breaker flips. To locate the reset button, consult the manufacturer's manual. Typically, the controller is located around the blower motor.

Reset the furnace by following these simple steps:

  1. Switch off the pilot light.
  2. Lower the thermostat temperature settings.
  3. Switch off the circuit breaker and the gas valve in successive order.
  4. Reconnect the circuit breaker then the gas valve.
  5. Push and clasp the reset button for about 30 seconds.
  6. Restore the thermostat settings to the desired temperature.

Technician Repair Gas Heater. Central Home Heating System. Rheem Furnace Won't Start - What Could Be Wrong

Final thoughts

Like any other appliance, the Rheem furnace requires regular maintenance to ensure that it serves you efficiently for a long time. In particular, cleaning the components such as the air filter and ignition switch will prevent the unit from malfunctioning due to dirt.

Identifying why the furnace will not start will help you chart an appropriate corrective measure. We hope the information in this article will help you identify the cause and ways to restore functionality in the furnace. If the issue persists, ask a furnace expert to determine the magnitude of damage and advise whether to repair or replace the furnace.

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