Pump won't prime

The pump runs but no water reaches the group head. Often happens after a tank refill, a long idle period, or a descaling cycle.

Why it matters — Almost always an air lock in the supply line. The pump is running dry, which can damage it if left for long.

Good to know

• The fix is simple: open the steam or hot-water tap while the pump runs. This vents the air through the boiler and primes the line.
• On some machines, removing the shower screen and pulsing the pump in short bursts also clears the air.