Water heater was on and lit when I arrived. Customer said they had to relight it twice before now. I noticed Combustion air vents on door near the floor was very dirty and maybe not allowing enough air to get into unit which I cleaned. Also cycled unit several times to get burner to come on and turn off and pilot still remains lit. Roof vent appears to be in good working order and is tall enough above roof. There were no error codes on unit as well. Seems to be working fine and Connor get it to malfunction. Customer will have someone keep an eye on it to see if it happens again.