Why is my Hayward heater h150 igniting and shutting off?

SOURCE: Problems with Hayward 100,000 Btu Heater

I am sorry to report that this is a very common problem for this heater. Here is more information than you want: http://forum.doityourself.com/pools-spas-hot-tubs/345253-hayward-h100id-ignites-but-cools-quickly.html

SOURCE: hayward heater not staying lit

possibly poor pilot adjustment or insuficient mv output from thermopile

SOURCE: hayward h250ed1 heater wont stay lit

Try cleaning your filter if dirty there will not be enough flow to llet heater fire. If filters clean you can try jumping the pressure switch.

SOURCE: H Series Pool & Spa Heater 400k Btu Propane Gas Milivolt Ignition H400p1: how do i fix the AO code on my hayward heater?...

AO will apply to your blower, blower tubing, or blower vacuum switch. You need to check these items.

SOURCE: My hayward h400ed2 heater starts for 2-3 seconds

Have you installed anything in your home that uses gas? Alot of times it due to low gas pressure.

When you checked the orfices did you actually remove them? or just stick a paperclip inside and clean them?

If the heater is firing ..even for 2-3 seconds the ignightor is fine. If it wasnt it wouldnt lite, period... bad call on hayward