4 likely possibilities:
- you are out of water in tank (suction side)
- you have a vacuum leak (air leaking into suction side)
- water pump is not building up pressure (pressure side leak)
- pump not running long enough (pressure side, has to fill water heater if empty)
Did you open a faucet and see if any water is coming out when pump is running? If normal stream of water is coming out, that's an indication of pressure side leak. If faucet spurts, or just has air coming out, it's more likely to be a vacuum side leak.
Fred W
2019 Flagstaff T21TBHW A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time