Pump start-up problem

[Poconos]

Sharkey,
Welcome to the forum.
This is puzzling. The loud buzzing and shutoff is an indication of a shorted starting capacitor. Some education....there are two windings in these motors. A running winding (RW) and a starting winding (SW). I hate typing. The SW has a capacitor in series with it, and also a centrifugal switch. Once up to speed the switch cuts out the starting winding. The SW is a low resistance winding compared to the RW. The capacitor is used to create a phase difference to start and determine the direction of rotation. If the capacitor or switch are open then the motor won't start and you'll hear a low humming sound. Eventually the thermal cutout will kick in. If the capacitor is shorted then you'll hear the loud hum/buzz and the thermal cutout will kick in quicker...like the 5 seconds you mention. Capacitors are cheap and do fail. What is puzzling is you stated it starts when you dump the water by opening the basket.
Some questions:
--I assume this is a new problem since you said the pump is < 1 year old?
--Did it start happening after the Winter? Maybe the cold caused a problem.
--Is the pump still under warranty?

I'm wondering about a series of coincidences here. Try opening the basket first time each day and see if it starts, before letting it try on its own normally. Quite possibly the thing heats up, trips the thermal cutout, then after a couple tries when you open the basket it starts. Who knows. I doubt the wiring is an issue because you said it does run eventually, the thermal cutout trips, and if the wiring gauge was too small it would at least start and run and maybe cycle between the start and run cycles.
Best I can do for now.
Al


Edit: Thinking more about this...a 2.5 HP motor is pretty big. You could be hearing just the hum of the running winding. Capacitors fail open or shorted, not intermittantly. Best guess at this time is crummy centrifugal switch contacts. Starter winding isn't in the circuit and you get no rotation. Something else to try is when it doesn't start, give the back end of the motor a couple sharp whacks with a short 2x4 (instead of a hammer) with power on....not enough to dent anything. Switch is located in the back end. Sometimes the shock will be enough to jar the contacts and start the thing. If that's the case, fix is simple. Clean the contacts. Tell you how if we get that far.
Got a model number of the pump and motor?
Al

(ajs-1)