Domakihub How to Bleed Air From a Pool Filter Safely
Release trapped air in minutes and restore full filtration pressure.
Reviewed by Domakihub pool pros · 2026-06-23 · 4 min read
Trapped air in a pool filter is one of the most common issues after a filter cartridge swap, seasonal startup, or any time the system runs dry. Left unchecked, that air pocket causes the pressure gauge to read high, reduces water flow through the returns, and forces the pump to work harder than it should. The video above shows the exact procedure on a real filter; the steps below give you everything you need to do it safely at your home, holiday rental, or hotel pool in Greece.
Why Air Gets Trapped in the Filter Tank
Every time you open a filter tank — whether to clean the cartridge, replace the media, or winterise the system — air fills the space where water was. When you reassemble and restart the pump, that air has nowhere to go on its own. It collects at the top of the tank and compresses as water is pushed in under pressure.
The result is a pressure gauge that climbs quickly past the normal operating range (typically 1–1.5 bar / 15–20 psi for most residential filters), sluggish return jets, and, in persistent cases, the pump losing prime altogether. Releasing that air takes less than two minutes once you know where the bleeder valve is.
Locating the Air Relief Valve
Almost every sand filter and cartridge filter has a small air relief valve — sometimes called a bleeder valve or pressure relief valve — mounted on the filter head or multiport valve. It usually looks like a small black or brass petcock, a thumb-screw, or a push-button fitting. On multiport sand filters it is almost always on top of the valve body; on cartridge filters it is typically on the lid or on a small port on the upper housing.
Before you touch anything, check the pump is running. You need the system under pressure to push the trapped air out. If you open the valve with the pump off, you will just let water drain rather than purging air efficiently.
Steps to Bleed Air From Your Pool Filter
- 1
Start the pump and let pressure build
Turn the pump on and allow it to run for 30 to 60 seconds. Watch the pressure gauge rise. If it stabilises at or below the normal operating range with good return flow, there may be no significant air pocket — but it is still worth a quick bleed after any reassembly. If pressure overshoots or the returns are weak, proceed immediately.
- 2
Locate the air relief valve on the filter head
Find the small bleeder valve or petcock at the top of your filter head or multiport valve. Have a rag or small bucket ready — a short burst of water will follow the air once purging is complete. Keep your face and hands clear of the valve opening; water under pressure can spray.
- 3
Open the valve slowly until air hisses out
Turn the valve counter-clockwise or press the push-button — no more than one full turn. You should hear a clear hiss as compressed air escapes. This is exactly what you want. Hold the valve open and keep the pump running throughout this step.
- 4
Wait for a steady stream of water, then close the valve
The hissing will shift to a steady stream of water once all the trapped air has been expelled. At that point, close the valve firmly — clockwise or release the button. Do not overtighten; these fittings are small and plastic threads strip easily. A snug, hand-tight close is sufficient.
- 5
Confirm pressure and return flow are normal
Check the pressure gauge immediately after closing the valve. It should drop to your filter's normal operating range. Walk to the return jets and confirm strong, even flow. If the gauge still reads high after bleeding, check for a clogged filter element, a closed valve elsewhere in the circuit, or a failing gauge — the air bleed itself is complete.
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FAQ
- How often should I bleed the air from my pool filter?
- Bleed the filter any time you open the tank — after a cartridge clean, a media change, or reconnecting pipes for the season. You should also bleed it if you notice unexpectedly high pressure or weak return flow during normal operation, as that can signal a developing air leak in the suction line.
- What if air keeps coming back after I bleed the filter?
- Persistent air usually means the system is drawing air in somewhere on the suction side — common culprits are a loose pump lid, a cracked strainer basket housing, a failing shaft seal, or a skimmer weir that drops below the water line. Fix the air entry point first; repeated bleeding is a symptom, not a solution.
- Is it safe to bleed the filter while the pump is running?
- Yes, and it is actually the correct method. The pump needs to be running so that system pressure pushes the trapped air out through the open valve. Opening the bleeder valve with the pump off will not purge air effectively — you will simply drain water from the top of the tank.