Hayward H400FDN won't stay lit

make sure wiring is correct especially if wired 120 volt read instructions inside panel

Burners don't have anything to do with the problem of pilot not lighting. Is the problem that flame will not 'stay' lit? Or you can't even get a flame to ignite? If former: possible bad pilot generator or bad gas valve. If latter, possible bad gas valve or no fuel to ignite.

Your pilot head is probably clogged with spiders. Disassemble and clean it out and it should start working.

Not at all uncommon. New heaters have to glaze over the file tile in the burner chamber and will often smoke and smell during the first week or so of operation.

Using a mirror, check to see that your flames are about 4" proud of the burner tubes when running. As long as they are and the color is a nice blue with little to no yellow/orange color, the heater is fine.

Follow the troubleshooting guide on page 36 of this owners manual. It will walk you through problem solving... http://www.haywardnet.com/products/Manuals/pdfs/Manual285.pdf

I had the same issue...you don't have enough gas pressure.