Where do you live and how cold does it get over winter? I’ve had some woes with the water pump IF i do not completely purge the system for winter. If the pump cycles on at intervals on standby it’s apparent that there is a bleed down somewhere, whether it’s an outflow or a backwash under pressure where the diaphragm is failing. I always have to bleed the air out of the hot water tank by cycling the pump on at 15 second intervals. Sometimes even with a full water tank it takes a while to completely purge the air. Opening the sink’s hot water tap when purging helps bleed the air. The air will be pressed out until a solid pressurized water stream emerges. I had a similar experience as yours and just replaced the pump which solved the problem. If you are good enough, you can tell by the sound of the pump whether it’s running at 100% or not. My original pump went through a cold winter with a trace of water left in it. That was enough to debilitate the pumps effectiveness.
2020 Ford F-350 XLT FX4 4WD SRW SB SC 7.3L Godzilla Gas TorqShift 10R140 397 amps dual Alt dual batts Frnt Dana 60; Rr Dana M275 E-locker 4.30's 4580/4320/4066# payload 7243# curb wt. 11,300# GVWR 5-er prepped. 2020 Northstar Laredo SC, 12v compressor fridge, cassette, 320w Solar sub zero insulation.