If you mean it won't stay running after the unit actually starts...meaning as soon as you release the red button it shuts off then you would need to clean the end of the thermocouple that screws into the gas valve....not the end that goes into the flame. Remove the small nut and clean the end with a small wire brush or scrape some metal off with a knife, then scrape some metal inside the valve where the end of the thermocouple seats.
But if you mean it will not start at all then you need to make sure gas in getting through the valve.
Answers & Comments
If you mean it won't stay running after the unit actually starts...meaning as soon as you release the red button it shuts off then you would need to clean the end of the thermocouple that screws into the gas valve....not the end that goes into the flame.
Remove the small nut and clean the end with a small wire brush or scrape some metal off with a knife, then scrape some metal inside the valve where the end of the thermocouple seats.
But if you mean it will not start at all then you need to make sure gas in getting through the valve.