Heater stopped heating two weeks ago and made a rattle sound near the manifold before shutting itself off. I replaced the igniter, thermal regulator and thermistor. Rattle is gone. Heater turns on, hot air blows out for 4-5 seconds and then luke warm air comes out. This process repeats itself. At times, the temp display spikes to around 115 degrees before it settles back down to the pool temp of around 76. I also replaced the hi limit switch with the same results. Wiring and connections all appear fine. After much reading, I'm thinking the mother board may need to be replaced. Thoughts?