Raypak 406A - IGN failure with no pilot light sensed.

[DavidG808]

Heater went out during winter, replaced board and igniter assembly. When I try to start the heater I can hear the spark, but pilot never lights.
End up with *No pilot sensed, Ignition failure*

Model P-R406A-EN-C

 

[ajw22]

Welcome to TFP.

Check static and dynamic gas pressures at the gas valve using a manometer.

 

[1poolman1]

Heater went out during winter, replaced board and igniter assembly. When I try to start the heater I can hear the spark, but pilot never lights.
End up with *No pilot sensed, Ignition failure*

Model P-R406A-EN-C

If the pilot never lights, be sure that all gas valves are open. Can't tell you how many service calls I've been on that the external gas valve was closed. No gas, no flame. It happens.
Are you sure the pilot doesn't light by visual inspection? They require one getting very low or using a small mirror (safest way) to verify. It could be lighting but not being sensed. The fork above the flame is the "flame sense" conductor in that heater.
First, clean any ground-wire (green wire) connections that you see in the cabinet. If that doesn't work, install a new ground (green) wire to one of the screws holding the burner tray in place after cleaning any rust/corrosion/etc. from the area and to a similar screw in the cabinet elsewhere doing the same cleaning.
If that doesn't work, verify that there is actually a lit pilot. If there is, the burner tray will have to be pulled out and the pilot assembly cleaned with a very mild abrasive, concentrating on the fork. Sometimes, on an older heater, I've seen that fork completely gone. If so, the pilot burner needs to be replaced.