Numerous posts about problems with the Pentair Minimax, prone to malfunction. One of the known issues is that the unit can keep busting ignitors. On my unit, every two months the ignitor element would crack apart and would have to spend another 75 bucks to get a new one.
Here is the genesis of the problem. The insulation panels that line sides of the firebox (underneath the heat exchanger) is prone to breakdown, with small particles of it breaking off and landing on the ignitor. Anything that touches the ignitor element will results in breakage. This is a bad design, but it is what it is.
Putting a small metal "cover" over the ignitor does help some (ignitor lasts 6 months instead), but the real solution would be to replace or repair the insulation panels. But they are not listed in the parts diagram for the unit, and it certainly is not worth it to purchase a new firebox. I don't know where to purchase this stuff--it is like a very tough styrofoam, about 3/4 of an inch thick.
I am thinking about painting over these panels with the heatproof paint used for barbeques. Maybe then the ignitors would not be damaged and need to be replaced.
Finally, some of you are going to say, "buy a new heater". Can't afford that right now...