I have a PacFab MiniMax 100 pool heater. The pilot remains on... but the burner will not ignite unless I hit/jar the heater. Any suggestions on what may need replacement or repair?

Pentair 472604 Igniter Replacement MiniMax NT STD Pool and Spa Heater

The ignitor is simple to replace, It is either a spark ignitor or a Hot surface ignitor. The above link will take you to a picture of the Hot surface ignitor, it is normal held onto the bottom of the burner tray, at right about the middle, by 1 or 2 sheet metal screws.

If a Spark style ignitor/electrode, then the bottom link is the one want to look at. Again, held in place the same way as above description.

Pentair 471090 Ignitor Electrode Replacement MiniMax 75 100 Pool and Spa...

Good Luck

Check igniter! You don't have the right spark? Lots of times it will short out & you can see the sparking elsewhere other than just at the gap at top of the igniter. The other thing to check is ensure that the orifice is completely clean at the pilot burner. A clean pilot orifice and the proper spark will ignite the heater.

Problem is an obstructed gas oriface. The burners light from the burner closest to the pilot assembly out like a dominoe effect. The explosion is because the gas has to make its way over to the pilot from a further burner thus filling the firebox full of gas before it ignites. This blockage is most commonly from a spider web inside the oriface itself. Pull the burner tray, remove the orifaces from the tray and look through each one cleaning them out with a toothpick from the backside. The orifaces should be threaded on the gas line coming off the gas valve (looks like a silver box inside the front panel)

Do you physically see the spark or are you just hearing it. You can also take the igniter wire off of the control module and disconnect the pilot gas tubing from the gas valve. Turn the heater on and wait to see if you hear and smell gas coming out of the gas valve. If there is no gas check for 24v at the PV connection on the module. If there is voltage the problem is the gas valve. If no voltage the problem is the ignition module. If there is gas I would replace the pilot and gas tubing.
Santa Clarita Pool Heater Repair

change the assembly valve

sounds like when burner kicks in it is diverting gas away from pilot. you have either too low pilot heighth or more likely an obstruction in pilot assembly

check pressure switch for proper adjustment and make sure filter is clean so system pressure is normal

Two reasons.

1. There is air in the gas line. Power down the heater and allow it to try igniting until lockout. If it locks out, repeat the process. Most lines will clear within 4-5 attempts to ignite.

2. A plugged burner orifice. Run a small pipe cleaner in the brass fittings on the burner tray. They may have small webs in them restricting gas flow.

If the unit is a Standard (STD on the plate inside) it has a flame sensor that may also be bad. That sensor is on the end of the single wire that is cloase to the ignitor wire near the burners. Also check for a losse ground wire on the heater.