Priming means removing trapped air from the water circuit and helping the pump draw a continuous supply of water from the tank. A pump may need priming after the water tank has run empty, following maintenance, after a filter change or when the machine has been unused for a long period.

Fill the water tank, make sure it is seated firmly and check that any water filter has been correctly prepared. Select the machine's hot-water function and allow it to attempt to dispense water. This can help the pump draw water through the circuit and push trapped air out. Follow the specific priming procedure for your machine where one is provided.

The hot-water function can provide a more direct route through the hydraulic system than trying to brew coffee. Running it allows the pump to attempt to establish continuous water flow without the additional resistance created by the coffee brewing process. Once a steady stream of water is produced, normal operation can usually be tested again.

If the machine won't draw water, temporarily removing the filter can be a useful troubleshooting step. A new filter containing trapped air, an incorrectly fitted filter or an older restricted filter can make it harder for the pump to establish water flow. If the machine primes without the filter, check or replace the filter before refitting it.

Initially you may hear a louder pump noise or see an uneven, spluttering water flow as air leaves the circuit. Successful priming should result in a steadier stream of water and the pump returning to its normal operating sound. You can then stop the hot-water function and test normal dispensing.

Don't repeatedly run the pump dry for extended periods. Recheck the water tank connection, tank outlet and filter, and make sure there is actually a clear supply of water to the pump. If the machine still cannot establish water flow, limescale, a blockage, faulty valve, weakened pump or another hydraulic fault may require further diagnosis.