Re: Pentair minimax has Flame but no hot water, please help!
Welcome to TFP!
A working pool heater will only raise the water temperature of the water passing through it by 1 to 10 degrees, with 2 to 4 degrees being typical. So it may not be immediately obvious that the heater is working even when it is.
That said, if it really isn't working, then the bypass valve has probably gotten stuck in the bypass position. Heaters want a specific amount of water passing through the heat exchanger, so they require you to run more water than that through them and then have an internal bypass which lets any water above the ideal amount bypass the heat exchanger. If the valve that controls that gets stuck or broken you can occasionally get into a situation where all of the water is bypassing the heat exchanger, though that isn't common.