I just setup an Autopilot CO2 burner powered by liquid propane. When the room reaches desired CO2 levels, the burner turns off, as it should. However, for 1-2 minutes after turning off there is a gassy smell coming from the burner. The smell dissipates within a couple minutes. Is this just the propane that was in the line before the solenoid valve shutoff the flow? Or should I be more concerned? All connections have been double checked for leaks with a soapy water spray.

Any input would be appreciated.