I am guessing that you leave it turned off until you want to warm the garage and when you do flip the switch to on, the pre-ignition blower starts up and after 15-30 seconds you will hear the ignitor start up to ignite the gas coming into the burner, these heaters do not have pilot lights, they use electronic ignitors. That is how mine works and though it takes that amount of time it starts up and the burners kick on and in short order I have heat coming from the blower. If it is not starting or the ignitor does not stop after ignition then you have a problem with the control board for it. I had that problem with mine last year and replaced the board and it works fine. I will agree that it takes a little longer for the gas to ignite when it is colder but it does fire up and runs fine and shuts down when it reaches the set temp.
