Sns code in modelp-m407a-en-c - Solar Rheem Gas Fired Pool & Spa Heater Model P-m266a-en-c

I think sns means sensor, perhaps the over temp sensor is defective, that would cause the shut down.

In the header... Plumbing side
And wire plugs onto heat / control assembly board.
SNS indicates that the Temperature Sensor is out of range! There are two thermistors within that sensor, and if there is a difference of 2 degrees, the board will throw a Fault Code: SNS
check for good connection at board, and ensure the sensor is all the way seated properly in its well.
otherwise, it may be bad.

temp sensor failure

SNS means the temp sensor is out of acceptable range. Could be the following:

1. Water temp is below 36 degrees F
2. The sensor contains 2 thermistors, if they are more than 2 degrees apart and SNS failure will occur
3.Loose or corroded connection at P1 on the main board
4. If the sensor has come out of the JACO fitting on the header, it may read a SNS failure.

Solution, visually inspect the connections for corrosion. If it looks ok, then replace the temp sensor.