Pilot lights but main burner won't

There seems to be a problem with the inflow of gas into the burner..Check the connection for any blocks, loose contacts etc.,

sometime if the heater has been sitting for days spiders get into the burner area or the area between the tank and the burner and make a web blocking the flow. I have taken a compressed air in a can like the ones you use for computers laptops and blow air up the shaft and around the burner wait 2 minutes then try again. Sometimes it takes 2 or 3 blowouts to work.

brand new unit doing same thing out of the box. I believe its the thermcouple safety sensor is bad. Left message for the company. bought at costco may just have to haul it back to them let them deal with it. Good luck all - seems to be a common problem - the h/w store guys knew what it was right away.