Rheem Classic 90 Plus Troubleshooting - Common Problems and Solutions

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Last updated: 
May 31, 2024

This Rheem Classic 90 Plus troubleshooting guide is a go-to solution if your furnace stops working. The goal of this guide is to help identify the problem and find the best solution. Keep in mind that it is NOT a Do-it-Yourself guide. It is useful in case of an emergency, only when an experienced service member is not available.

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The Rheem Gas furnaces are energy efficient units, designed to work for a long time. The heat exchanger made of stainless and aluminized steel provides corrosion resistance. Moreover, the blower section is insulated to decrease noise. There is also a direct spark mechanism ignites the Rheems furnace pilot light, for quick lighting.

Rheem Classic 90 structure

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Rheem Classic 90 Plus Furnace - Common Issues

Common issues you may encounter during the Rheem Classic 90 Plus troubleshooting.

Periodically perform standard maintenance to ensure the furnace operates satisfactorily for years. Always clean your unit before starting it for the winter season.

  • The first common issue is the Furnace is not putting out heat. The furnace is turned on, and you hear it working, but there is no heat coming out of the vents.
  • The furnace is not igniting. You push on the igniter, and it will not ignite the unit.
  • The heater is running all the time even when you lower the set point. It does not seem to stop running or shut off when it reaches the setpoint.
  • The unit is running hotter than normal. When you touch the housing, you feel it is hot to the touch.
  • The unit is heating certain rooms and not others. Some rooms do not get any heat while others are comfortably warm.
  • The gas bill is running exceptionally high compared to the average winter usage. The gas company is sending you notices of your higher energy consumption.
  • You see too much Soot or detect a strong gas smell.

Tools You Will Need

Caution: before you start the troubleshooting, turn off the furnace. Unplug from the power supply and remove the control door. Allow the gas in the lines to clear by turning off the gas control switch and wait 5 minutes. Make sure you do not smell any gas. If you detect a strong gas smell, stop and leave your house. Immediately contact the local fire department and your gas company.

To effectively fix the common problem, you will need the following tools:

  • A ¼ inch or a 5/16 inch nut driver or a bit
  • a cordless drill used to service the parts
  • An insulated handle screwdriver
  • A handheld vacuum
  • A Multi-Meter used to test the Thermocouple.

Rheem furnace inside view

Rheem Classic 90 Plus Furnace Troubleshooting

Please follow this Rheem Classic 90 Plus troubleshooting guide to fix common problems.
Some of the troubleshooting tips that might save you time are as listed below.

1. Power

One of the most overlooked issues is Power. Always check that your furnace is plugged into the wall outlet and turned on. Check to see if the thermostat setpoint is higher than the indoor temperature. Press the reset button, no more than twice to reset the unit. If there is no power coming into the unit then, reset the circuit breaker if it was tripped off. Replace fuses with broken wires or if they turned black.

2. Thermostat Batteries

Check the thermostat batteries and replace them when necessary.

3. The Furnace

If you there is no heat out of the unit and no gas smell, then, turn off the furnace. Unplug from the power supply and remove the control door. Turn off the gas control switch and wait 5 minutes then remove the filter from the front panel. Replace the filter or remove the accumulated dirt and debris with a hand-held vacuum. Clean the filter with warm water and a few drops of dishwashing liquid. Rinse and air-dry thoroughly before inserting it in the furnace. Turn the switch to "On" position and close the control door. Turn on the furnace power.

4. The Igniter

If the igniter not on, then relight the pilot if it was turned off. Clean around the pilot light if it does not light and dry up any water. Use an insulated handle screwdriver to test the transformer. Check if the current arches when it touches one of the contacts. Replace the transformer if the current is weak. Replace any corroded or broken wires and electrodes.
Change the pilot thermocouple if all the previous items check.

5. The Combustion Chamber

If the unit is running hot, place your hand near the door of the combustion chamber. If it is hot, then the system has a blockage. Clean the chimney, the duct pipe, and the combustion chamber. Check and replace the heat exchanger and gaskets if broken.

6. The Vent

Check when the heat comes on if it heats up certain rooms only. If so, place your hand on each room’s vent and, if you don’t feel any airflow coming out of those vents, then clean their ducts. Replace any crushed or broken exterior piping. Clear any obstruction from interior vents.

7. Replacing the Thermostat

If your heater is running all the time even when you lower the setpoint, then replace the thermostat.

8. Efficient Appliances

If your gas bill is higher than your average, then you may have added an inefficient appliance. It may increase your energy usage.

9. Emergency Advice

If you see Soot or smell gas, immediately turn off your furnace and leave the house. Call the fire department or the local gas company. Return home when you get a clear communication that it is safe to return.

Caution Notes

Immediately turn off your furnace if you smell gas. Contact your gas company or the fire department and leave the house. Do not enter your home until you receive the clear signal.
Keep all combustible material away from the unit.
Remain clear of heat sources while performing the Rheem Classic 90 Plus troubleshooting.

Be aware of dust and allergens while cleaning your filter. Please use precautions if you have any respiratory issue.
Immediately, contact your physician if you experience a severe allergic reaction. Or go to the nearest emergency room if you have difficulty breathing or swelling of the tongue.


We hope the Rheem Classic 90 Plus troubleshooting guide shed light on problems your furnace may encounter. And the recommended fixes needed during its lifetime. If you find this information helpful, leave us a comment in the section below. We welcome your feedback and value your input.

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