Thats a normal display, not a code, after installing heaters brand new thats what they say. Service heater is an issue, like pool guy said, youll remove the door on the side of the control, turn the heater on, and the second it shuts off and the service heater light comes on, look at the pc board on the flip side of the control panel.

Let's get more info!
Take off the front panel of the heater... If you have space to kneel down and look under the display to the back of the circuit board then front panel us all you need to remove for now, if it's too difficult to see or if you have no space then the top panel would need to be loosened by removing the wing nuts on each corner. If you do loosen the top panek be careful when lifting it as the wires are still connected!

Turn heater on and tgen check the back of the board to see which tiny red lights are on , take note of which are on and what abbreviation is next to the illuminated light.
this will tell you which area of the heater the issue is then repost with that info