If your pump has a low pitched hum, but no water delivery, it may be in by in by-pass mode. The first thing I would check is for back-pressure in the outside CW connection. Remove the cap and reach in with your finger and press the check valve button to release any pressure. Stand to the side though, as you may get a bath if pressure is there.
'07 K3500 Silverado LT Crew Duramax (LBZ)
2016 Salem 27RKSS
1984 CHEV SCOTTSDALE K20 2GCGK24J0E1XXXXXX (Chevrolet Legends-Class of 2019)
"...exhaust fluid? We don't need no stinkin' exhaust fluid"