How to Prevent & Clear Air Locks After Refilling Your Hot Tub

You’ve just finished draining, scrubbing, and refilling your hot tub with fresh water. You flip the breaker back on, eager for a soak, but instead of a rushing torrent of warm water, you hear a faint humming, maybe some clicking, and absolutely nothing comes out of the jets. A few moments later, your control panel flashes a "FLO", "FL1", "FL2", or "DRY" error code.

What you are experiencing is an air lock.

Air locks are one of the most common issues hot tub owners face after a refill. While it can be alarming, it doesn’t mean your pump is broken. It simply means a bubble of air is trapped inside the plumbing, blocking the pump from priming and circulating water.

Here is exactly how to prevent air locks from happening in the first place, and how to quickly clear one if you’re already stuck with error codes.

What Causes a Hot Tub Air Lock?

When you drain your spa, the entire plumbing network empties and fills with air. When you refill it by simply throwing a garden hose into the footwell, the rising water level seals off the jet faces and suction grates before the internal pipes can fill.

This traps a massive pocket of air inside the pumps and heater tube. Since hot tub pumps are designed to push water, not air, the impeller just spins uselessly in the air bubble without creating the suction (prime) needed to move water.

How to Prevent an Air Lock (The Right Way to Refill)

The absolute easiest way to deal with an air lock is to prevent it from ever forming. Almost all air locks happen because of where the garden hose is placed during a refill.

The "Filter Compartment" Refill Method:

1. Remove the Filters: Take your filter cartridges entirely out of the spa.
2. Insert the Hose: Place your garden hose directly down into the open filter pipe (standpipe), rather than throwing it into the main footwell.
3. Fill Through the plumbing: By filling through the filter compartment, water enters the spa from the inside out, flooding the pumps, heater, and lowest plumbing lines first. As the water rises, it pushes the air out through the jets, naturally venting the system.
4. Reinstall and Power Up: Once the water reaches the designated fill line (usually just touching the bottom of the headrests or covering the highest jets), remove the hose, put the filters back, and turn on the breaker.

How to Clear an Air Lock: 3 Step-by-Step Methods

If you didn’t fill through the filter and your spa has no jet pressure, don’t panic. Try these troubleshooting methods to get the air out.

Method 1: The "Jet Cycle" Burping Method (Easiest)

Often, you can "burp" the air out by cycling the jets to force the pocket through.

1. Remove Filter: Take your filters out to maximize water flow.
2. Activate the Jets: Turn the jets on "High" for 10 to 15 seconds, then turn them "Off".
3. Repeat: Repeat this cycle 3 to 5 times. You may see bubbles erupting from the jets or hear a rushing sound as the air escapes.
4. Important: Do not let the pump run on high for more than 15 seconds if no water is moving, or you risk overheating the pump.

Method 2: The Bleed Valve Release

Most modern hot tub pumps have a small "bleed valve" designed specifically to vent trapped air.

1. Turn Off Power: Cut the power at the main GFCI breaker. Never work inside the equipment cabinet with the power on.
2. Access the Equipment: Open the side panel to access your pumps.
3. Locate the Bleed Valve: Look for a small thumbscrew (often black or plastic) on the front face of the pump housing (the wet end).
4. Loosen Slowly: Turn it counterclockwise by hand. You will hear air hissing out.
5. Close When Wet: As soon as a steady stream of water starts to trickle out, tighten the screw back up (hand-tight only; do not use tools, as the plastic can crack).
6. Turn Power On: Close the panel and turn the breaker back on.

Method 3: Loosening the Pump Union

If your pump doesn't have a bleed valve, you can achieve the same result by slightly loosening the main plumbing union on the pump.

1. Shut Off Power: Confirm the breaker is completely off.
2. Identify the Intake/Output Union: Locate the large, hand-tightened collar (the union) that connects the PVC plumbing to the pump.
3. Loosen Slightly: Carefully turn the collar counterclockwise (using channel locks or by hand if loose) just enough to break the seal.
4. Listen and Watch: Listen for the hiss of escaping air. A small amount of water will begin to drip.
5. Tighten Immediately: As soon as you see a steady trickle of water (and no more hissing), hand-tighten the collar back up firmly. Make sure it’s snug so it doesn't leak under pressure.
6. Test: Turn the breaker back on and run the jets.

Still Getting Error Codes? Call the Pros

If you’ve tried the "burping" and venting methods and your pump still refuses to prime, you might be dealing with a worn pump impeller, a faulty sensor, or a clogged plumbing line.

Before you risk running your pump dry and causing permanent motor or heater damage, let our expert service technicians handle it. At Main Street Pools, we don’t just resolve stubborn air locks, we can handle the entire draining, line flushing, inspection, and refilling process for you through our Hot Tub Drain, Clean & Comprehensive Health Check.

Book your service with Main Street Pools today! Or call us at 905-862-4040 for professional, on-site support.