Heater won't light
I have a Hayward 400k btu heater that is about 4 years old. When I turn the heater on the fan starts I hear a click and then a quick poof sound with some small flames comin out of the top. Its night time sothe flames are noticeable. I wouldn't be ble to see them if it was during the day. Does this maybe one more time and then it lights. I notice it happens more often if I go a week or so without using the heater. This just started a few months ago. Does something need to be cleaned?