Spa Airlock After a Refill: How to Clear It

Last updated: October 2026

Here's a pattern every spa tech recognizes: the tub worked fine on Saturday. On Sunday the owner drained it, cleaned it, refilled it — and by Sunday night it's showing flow codes, the pump sounds like it's gargling gravel, and the heater refuses to run. Coincidences that perfect are rarely hardware. They're air.

Why refills trap air

Draining a spa empties more than the shell. The pump volute and the heater loop drain too, and they sit at the plumbing's high points. When you refill by running a hose over the side, water rises in the shell while air stays pocketed in the pump and heater — the two places that most need water. The pump then spins against air instead of water (weak, surging, or no flow), and the heater sees little or no water moving through it.

Each control system reports that in its own accent: Balboa shows FLO and the dry-heater messages dr / drY; Gecko shows FLO or trips its high limit (HL); an inflatable Bestway pump lands on E02. Different letters, same bubble.

The bleed: clearing an airlock

1. Stop the strain first. Don't let the pump run on against air while you read guides — power off at the breaker. A dry-running pump and heater are how a free problem becomes a parts invoice.
2. Find the bleed point. The highest union on the pump's discharge side — the large threaded collar where plumbing leaves the pump. Some pumps have a small dedicated bleed screw instead; it's the same idea. Exact location varies by model; your equipment bay will show you.
3. Loosen a quarter-turn (breaker still off). Trapped air hisses out. The moment water seeps steadily instead of sputtering, retighten the union.
4. Power on and pulse the jets. Run the jets on high in 20–30 second bursts, resting between bursts. Watch the codes and listen: jet pressure should steady and the gargling should fade as the last air works through.
5. Repeat once if needed. Stubborn pockets sometimes take a second bleed after the first round of bursts moves air closer to the pump.

Prevention: fill through the filter well

The airlock is mostly a filling-method problem, so fix the method and most refill dramas never start:

• Put the hose down inside the filter well (filter removed) so incoming water is pushed through the plumbing as the spa fills, instead of filling the shell around dry pipes.
• Open every jet before you start, and don't test-run pumps at half-full "just to see" — that's priming against air on purpose.
• Fill to the full operating level before powering up, then let priming mode finish (Balboa shows Pr — that's the pack priming itself, not a fault) before judging any display.
• Bleed once, proactively, right after a refill if your pump has an accessible bleed point — thirty seconds that pre-empts the whole code cycle.

Inflatables: same physics, smaller pump

A Bestway/SaluSpa pump airlocks after a refill or a pump reattachment the same way, and shows it as E02 or a pump that runs without moving water. The fixes are cousins: confirm the stopper caps are off, seat the pump couplings fully, and start filtration with the filter set out for the first minutes so air purges freely — then install the cartridges once flow is steady. Don't let the little pump grind dry either; it has the same dry-run limits as its big relatives.

If your post-refill codes outlast two bleeds and a filter-out test, the troubleshooter will route you to the right branch — air was the likely suspect, not the only one.