An airlock occurs when air enters a section of the water circuit that would normally contain water. Instead of drawing a continuous column of water from the tank, the pump is attempting to move trapped air.

This can result in a buzzing or pumping sound with little or no water reaching the outlet. It commonly becomes apparent after the water tank has run empty, the machine has been stored without water or work has been carried out on the water supply or filter.

A common sign is a pump that can clearly be heard operating but produces no water or only an intermittent flow. The problem may appear suddenly after refilling an empty tank or replacing a water filter.

Before diagnosing an airlock, make sure the tank is full and correctly fitted and that its outlet isn't obstructed. If removing the water filter immediately restores normal flow, the filter or trapped air within it is more likely to be responsible.

Yes. When the machine attempts to draw water from an empty tank, air can enter the inlet pipework. Refilling the tank doesn't necessarily remove that air immediately.

The pump may subsequently struggle to establish a continuous water supply. This is why using the machine's water-circuit filling, priming, rinse or hot-water procedure can be necessary after the system has been allowed to run completely dry.

It can. A dry filter contains air, and if it isn't prepared correctly before installation, some of that air can enter the machine's water circuit. The filter also creates additional resistance at the pump inlet.

If water delivery stops immediately after a filter change, remove the filter and test again. If flow returns, properly saturate and activate the filter according to its instructions before reinstalling it.

Sometimes a short priming or water-delivery cycle will move the trapped air, but continuously running a pump dry isn't a good troubleshooting method.

Fill and correctly seat the tank, remove any questionable filter and use the machine's designated priming, hot-water or rinse procedure. You're trying to provide the pump with an unrestricted water supply so it can replace the trapped air with water, rather than simply making the pump run for longer.

If you've confirmed that water can leave the tank, removed a potentially restrictive filter, correctly primed the circuit and still cannot establish flow, further investigation is justified.

Possible restrictions can occur elsewhere in the hydraulic system, including scale deposits or blocked water passages. A pump that runs but cannot move water also needs to be distinguished from a pump that isn't operating at all. Internal diagnosis should be left to someone competent to work safely on the appliance.