I've had this happen before with pumps, what worked for me was to open it up, give the impeller a spin in water and then put it back together. Usually does the trickSwapped my tanks just over a 2 weeks ago, planned to use an extra pump I had to pump water from old display right to new display. Idiot me didn’t check the pump (it worked 2 months ago) and day of change after turning off tanks came to find pump didn’t work. Needless to say had to replan and began scooping jugs of water out