Hayward Universal H-Series Pool Heater won't start up and stay running

i noticed that this pool heater almost worked correctly but would shut off in the middle of
the start up cycle. in order to get the igniter heating up and glowing, a number of sensors and switches have to be operating correctly. the igniter would glow for 15 seconds and then the gas
would come on a second or two and then the unit would shut off.

i found out that if i engaged the gas value with an external power source only after the igniter was glowing for a 10 seconds, the burners would run as long as the power source was enabled. this provided me confidence that the heater was almost working. Warning, don't try to do this unless you feel extremely safe with this step! You can't keep the gas value going if it's not burning the gas. The value should be shut off quickly (few seconds) if the burners don't light.

i also noticed that an error code was tripped "FL". This code indicated that a flame was present even when the internal controller was telling the heater to stay off (keep the gas value off). This error code shows me that the flame detector circuit was working fine and that is one less issue for me to be concerned with.