I have a Rheem 3 ton H&A unit that 90% of the time will world great for a few minutes and then the gas shuts off and the fan continues to run. 10% of time it will heat properly until the thermostat shuts it off. The unit has two switches. One is a thermal type switch and the other a small button type(popper) switch. Do you have suggestions of how to check the problem?
Thanks
Gotitans

Soulds like you may have a limit problem. How is your air filter?