Airlock in Shower Pump — How to Bleed It
If your shower pump is running but delivering only a trickle of water, you've almost certainly got an airlock. This is one of the most common issues with pumped shower systems, particularly in homes with additional storeys or those relying on gravity-fed cold water tanks. Airlocks typically develop after maintenance work, tank refilling, or if pipework has been disturbed — and the good news is that bleeding the pump is usually a straightforward five-minute job you can tackle yourself. This guide walks you through the process step by step, explains what's actually happening inside the pump, and covers what to do if the problem keeps coming back. If you're uncomfortable working with water systems or the issue persists after bleeding, it's time to bring in a qualified plumber.
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Most likely cause & what to check
An airlock occurs when air gets trapped in the pump, preventing water from flowing. You'll hear the motor running and feel vibration, but the shower will produce very little or no water.
Switch off the pump at the fused spur. Close both isolation valves on the hot and cold inlets.
Place a towel and bucket under the pump. Slowly undo the cold inlet union nut — water will flow. Let it run for 10–15 seconds to flush out the trapped air. Retighten the union nut.
Repeat on the hot water inlet union if the cold side alone didn't clear it.
Open both isolation valves fully and switch the fused spur back on. Run the shower — pressure should return within a few seconds.
If airlocks keep returning, the cold water tank level may be too low or the pump inlet pipework has a high point that regularly traps air. A plumber can reroute the inlet to fix this permanently.
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Frequently asked questions
How do I know if my shower pump has an airlock rather than another fault?
You'll hear the pump motor humming and feel vibration through the pipework, but water flow will be drastically reduced or absent. If the pump were completely broken or the electrics had failed, you'd hear nothing at all. Airlocks are the most common reason for a running pump with poor pressure.
Is it safe to bleed the pump myself, or should I call a plumber?
Bleeding an airlock is a safe DIY job — you're simply releasing trapped air through union nuts. Just switch off the pump first and have a bucket handy to catch water. If you're not confident handling water fittings or the problem returns repeatedly, that's when a professional should investigate the root cause.
Why do airlocks keep happening after I've bled the pump once?
Recurring airlocks usually mean the cold water tank level is dropping too low, or the inlet pipework has a high point where air naturally collects. A plumber can assess your pipework layout and either top up the tank provision or reroute pipework to eliminate the high point permanently.
Do I need to bleed both the hot and cold sides, or just one?
Start with the cold inlet — this clears most airlocks. If pressure is still low after retightening, move on to the hot inlet union. Both sides can trap air, but the cold side is usually the culprit since it's directly fed from the tank.
What should I do if water keeps spraying out when I undo the union nut?
That's normal and actually a good sign — it means the pump was under pressure. Place the bucket underneath, open it slowly rather than all at once, and be ready with a towel. The flow will ease once air escapes and pressure equalises.
How long should I let water run when bleeding the pump?
Ten to fifteen seconds is usually enough to flush out trapped air bubbles. You don't need to run it for ages — you'll notice the flow becomes steadier as air clears. If it's still trickling after that, close the union and try the hot inlet.