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Rheem classic 90 plus troubleshooting - PartsAPS

rheem classic 90 plus troubleshooting

Rheem Classic 90 Plus gas furnaces are designed for utility rooms, closets, alcoves, or crawl spaces. These are the high-efficiency line of downflow or horizontal gas furnaces. Rheem classic 90 plus has many features including low profile 34 inches, molded permanent filters, optional indoor or outdoor combustion air, condensate drain, and more. It's not a matter that your furnace has a lot of features, sometimes, it stops working. So, here is the Rheem Classic 90 Plus troubleshooting guide when it stops working.

Rheem Classic 90 Plus Troubleshooting

This Rheem C90 plus furnace troubleshooting guide is to help you detect the problem and find the best solution.

Rheem Classic 90 Plus Common Problems

  • The furnace is not producing heat. Your unit is turned on and you heat sound as it works but not produce heat out of the vents.
  • Rheem furnace is not igniting.
  • The heater is running all the time even when you set it at the lower point. It won't stop operating or shut off when it reaches the set point.
  • The furnace is running hotter than normal. When you touch the housing, you can feel it warm.
  • Your unit is heating some rooms but not others. Some rooms do not get any heat.
  • The utility bill is high compared to the average winter usage.
  • Detect a strong gas smell from your furnace.

Above are the common problems that are occurred with your Rheem Classic 90 Plus furnace. You can follow the troubleshooting tips below to fix these issues.

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How to Troubleshoot Rheem 90 Plus?

Before you start the Rheem C90 Plus troubleshooting, make sure to turn off the unit. Remove the plug from the outlet and remove the unit's control door. Turn off the gas control switch and allow the gas in the supply lines for 5 minutes. You should not smell the gas. If you get the strong smell, immediately shut off the gas control switch and leave the house. You can contact the local fire department.

Power Issues

Problems with power are common things. So, you should always first check that your furnace is getting power, plugged into the power outlet, and turned on. If your unit not receiving power, you need to reset the circuit breaker if it is tripped off. Need to be replaced the fuse if it is blown. Also, check for broken wires if they turned black.

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Check to see if the thermostat setpoint is higher than the normal temperature. If it is set at a higher point, you have to press the reset button twice. Also, inspect the thermostat batteries and replace them if necessary.


When turn on your furnace and no heat and no gas smell from the unit, you need to shut off the unit. Immediately, unplug the furnace from the power supply source and remove the control door. Now turn off the gas control switch and wait for some time. After that, you have to remove the filter from the front panel.

Check if the filter is accumulated with dirt and debris. If so, clean the filter with a few drops of dishwashing liquid and warm water. Once the cleaning has been done, rinse and air-dry thoroughly before inserting it in the Rheem furnace. Now, turn the switch to the ON position and close the control door. Finally, turn on the power to the furnace.

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If the igniter on the furnace not on, you will need to relight the pilot. Make sure to clean around the pilot light if it does not light and dry up any water.

Test the transformer by using an insulated screwdriver. And, check if the power arches when the screwdriver touches one of the contacts. Replace the transformer if the current is weak. Also, you need to replace any broken or corroded wires as well as electrodes.

You will have to check the pilot thermocouple and change it if necessary.

Combustion Chamber

If your Rheem C90 is running hot, check by placing your hand near the combustion chamber door. If you notice hot at the door of the combustion, then consider that the system has a blockage. You need to clean the duct pipe, chimney, and combustion chamber as well.

Additionally, you have to check and replace the heat exchanger and gaskets if broken.


If the unit heats up certain rooms only, check the vents in your rooms. If there is dirt, you should clean their ducts. Replace any broken exterior piping. Also, clear obstructions from interior vents if any existed.

Final Words

However, you can prevent Rheem Classic 90 Plus furnace problems with standard maintenance. You must perform regular maintenance to ensure the unit operates satisfactorily for years. Moreover, clean the furnace every time before starting it. We hope this guide helped you on Rheem C90 furnace problems. If you smell gas, immediately turn off your furnace.

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