How to troubleshoot the air lock on a boiler

Written by ian kelly
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How to troubleshoot the air lock on a boiler
If your hot water stops flowing, a simple procedure will clear the plumbing air lock. (Jupiterimages/Comstock/Getty Images)

If the flow from your hot water tap drops to a trickle or stops altogether, and you hear a hissing or sputtering noise coming from the faucet, there’s an air lock in your system. Try opening the hot water tap farthest from your hot water tank. If you’re lucky, the hissing noise will continue for a few minutes until all the trapped air in the system escapes. If that fails, a simple procedure will clear the blockage, especially if you have a washing machine connected to hot and cold water outlets.

Skill level:

Things you need

  • Bucket
  • Channel pliers
  • Short length of hose (if required)
  • Two hose clamps (if required)

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  1. 1

    Slide your washing machine away from the wall and close both the hot and cold water shut off valves situated on the wall behind the machine.

  2. 2

    Place a bucket under the hose connectors on the back of the machine to catch any escaping water. Disconnect both hose couplings from your washing machine by gripping them with a pair of channel pliers and loosening them in an anticlockwise direction.

  3. 3

    Remove the hot water hose from the red shut-off valve. Connect the cold water hose leading from the blue shut-off valve to the hot water shut-off valve and tighten the coupling.

  4. 4

    Open both shut-off valves and wait two or three minutes. Your household’s cold water pressure of between 3.5 and 7 bars is greater than the static hot water pressure leading from your hot water tank; therefore cold water pressure will blow the bubble of trapped air out into your hot water tank.

  5. 5

    Close both shut-off valves and open a hot water tap to see if the blockage has cleared. If not, open both valves and wait another four or five minutes to allow all the air to escape, and then reconnect the hoses to your washing machine.

  6. 6

    Go to Step 7 if you do not have a hot and cold water washing machine.

  7. 7

    Cut off a 24 cm length of a hose with an inside diameter large enough to fit over the spouts on your kitchen or bathroom hot and cold water taps.

  8. 8

    Slide two screw type hose clamps onto the short length of hose. Connect one end to the cold water tap and the other end to the hot water tap and tighten both hose clamps.

  9. 9

    Turn on both taps to clear the air lock in your system as described above. Turn off the taps after the blockage has cleared, remove the connecting hose and stow it away to use the next time you encounter the problem.

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