Filling your spa correctly the first time — or after a drain and refill — prevents an air lock, a condition where trapped air in the plumbing keeps the pumps from circulating water properly.
Locate the filter housing and remove both filters by unscrewing them.
American Whirlpool: there's a small screen over the standpipe opening that keeps the hose from going down into it — just rest the hose on top of the standpipe. Vita Spa: the standpipe is open, so push the hose down into it as far as it'll comfortably go.
Turn on the water. Filling through the standpipe pushes water straight through the plumbing and forces trapped air out — that's what prevents an air lock. Filling from the top of the spa skips this step entirely, which is why we don't recommend it.
Fill from that standpipe for 15–20 minutes.
Move the hose to the second filter standpipe (same brand-specific placement as above) and continue filling, so both plumbing sides get purged.
Fill until the water reaches the WATERLINE mark on the face of the filter basket — both brands have this mark, and it's the most reliable way to know you've filled to the right level.
Reinstall both filters.
Restore power and begin startup.
Heating up
Expect roughly 15 minutes per degree on a 220V spa. Going from 60°F to 100°F takes about 10 hours — leave the cover on to retain heat while it climbs.
Full technical detail: Vita Spa Owner's Manual / American Whirlpool Owner's Manual