**A failed thermocouple is a likely cause, but the symptom alone doesn’t confirm it.** Holding the knob down manually opens the pilot gas valve. Once you release it, the heated thermocouple must produce enough electrical voltage to keep the safety valve open.

Two minutes usually exceeds the required warm-up time; for example, [Resideo’s lighting instructions](https://customer.resideo.com/resources/Techlit/TechLitDocuments/69-0000s/69-0668.pdf) specify about one minute. Possible causes include:

- A weak or misdirected pilot flame that doesn’t heat the thermocouple tip adequately.
- A loose thermocouple connection or a failed thermocouple.
- A faulty safety mechanism in the gas valve.

Check your furnace’s lighting instructions and, through the normal viewing opening, whether the pilot flame reaches the thermocouple tip. An HVAC technician can check the flame, connection, and thermocouple voltage to determine which part needs replacing. [Resideo’s troubleshooting guidance](https://customer.resideo.com/resources/Techlit/TechLitDocuments/69-0000s/69-0624.pdf) calls for voltage testing when the pilot keeps going out upon release.

For now, turn the control to **OFF**. Never wedge the knob down or bypass the safety device. **If you smell gas, leave immediately, avoid electrical switches and flames, and call your gas utility’s emergency line from outside.** [Gas-leak safety guidance](https://www.nwnatural.com/safety/smell-natural-gas)