Temp switched from F to C reading?

i would get the OBD codes read as should give code for sensor/switch at fault , i would guess a temp seder switch but OBD will be more accurate

Celsius IS a temperature measured in degrees, as is Fahrenheit.
I don't know about your rig, but my guess is that you can hold down the menu button or go to "set up". Get the temp to flash, push the up/down button until the change. If you are needing to make a manual calculation, Celsius is changed to Fahrenheit by multiplying the reading X9, dividing that by 5, and adding 32 to that number.
Ex== 30 degrees C to F is 30X9/5+32= 86 degrees.

Your "knock sensor" kicks in??? That means there must be a knock detected and the engine is doing what it is supposed to do. How do you know your timing is 4-6 degrees at 60 mph?

Balboa switched to using two temp sensors a few years ago. So you won't find a flow or pressure switch. One of your temp sensors may be bad. With out knowing which pack you have I can't do much else for you.
I had a few issues with retro fitting these packs in older hot tubs. If the sensors read more than 2 degrees in diffrence the pack will either give you a flow or overheat message. Depending on witch one reads higher. Try swithing them by swapping them where they plug in at the board. If your still getting the same error you may have a flow issue. If this proves to be the case you can plumb in a by-pass allowing some of the water past the heater. It's not recommended by balboa but has solved their temp sensor errors for me in the past.
Also try putting it in test mode. You'll have to look up how to do it for your model. This is done with a dip switch on the board. Then read what the temp reading on temp sensor one and two is. If the reading are more than 2 degrees apart and your absolutly sure the sensors are good create a by-pass. This will solve the issue. Also be sure to put a ball valve on your by-pass to allow for ajustment so that you can get the maximum flow thru the heater w/ out getting the HL error.

The Warm is the actual temp of the roast. The roast will need to exceed X amount of degrees before it reads out for you. Some are 100 some are 120. I would refur to your manual or their web site for the actual threshold when it will actually start to read.
Thanks,
Shawn

Double check to make sure he put the sensor on the inlet side of the heater. Sounds like you are reading temp of water leaving the heater.

on electronic stats check that the temp is in sync with the room temp on touch pad push the menu button the two temps should be the same if not touch temp till reads correct

change the assembly valve

Turn the temp set knobs on the front of the heater all the way up do both pool & spa temp.
If that doesn't help flip the selector switch on the front of the heater the pool temp. This switch doesn't control what heats up Pool or spa it just selects the heater on and which thermistat to use