The dreaded light came on for the past couple of years and consequently we replaced the pump and later both pump and valve. Still there. Could hear the pump come on, noisily, and the light also. After chasing a lot of things I bought both the solenoid valve and the pump relay. We replaced the valve and have since been free of the light. The solenoid valve obviously was not working and the pump was having to work hard pushing aid against a closed system.

My suggestion as far as diagnostics goes: if you hear the pump and it is noisy, change the solenoid valve first. Could have saved me a lot of time and money.

dick