I have an older Hayward H400ED1 heater it just recently started acting up. When I switch it on you can hear the electric igniter for a few seconds and then the flame fires up. About 3-5 seconds later the flame cuts off. There is a "system normal" and "heating" light the system normal light stays on the whole time while this happens and the heating light comes on and off with the flame. One thing I noticed is before when the heater worked properly when I would turn it on you can hear the igniter and once the flame kicked on the igniter would kick off, but now when the flame kicks on I can still hear the igniter for the few seconds while the flame is on then once the igniter cuts off the flame shuts off as well. Its almost like the heater thinks the flame wasn't ignited after several seconds (when it actually is) so it cuts it off.
Is there some kind of sensor that tells the heater once the flame is on that I can clean or replace. What do you guys recommend?