Pressure Pulsing or Surging

Symptoms

• Pressure repeatedly surges and drops in a rhythmic pattern
• The machine sound fluctuates between high and low revs
• Jet alternates between strong and weak every few seconds
• Pulsing occurs from the moment the machine is switched on

Likely Causes

1. Air trapped in the pump or hose (common on first use or after storage)
2. Water supply flow rate is too low to keep the pump fed
3. Inlet hose is kinked or partially blocked
4. Non-return valve is partially obstructed
5. Nozzle orifice is partially blocked, causing back-pressure

Step-by-step Fix

1. Confirm the inlet tap is fully open. Partially open taps restrict flow and cause the pump to cavitate, producing the pulsing symptom.
2. With the machine switched off, disconnect the high-pressure hose from the trigger gun. Switch on the machine briefly to flush air from the system — water should flow steadily from the outlet. Switch off and reconnect the hose.
3. Straighten the inlet garden hose along its full length. A single kink 3–4 metres back is enough to starve the pump.
4. Remove and inspect the nozzle. A partially blocked orifice creates enough back-pressure to cause pulsing. Clean the orifice with a needle or clearing pin.
5. If using a long extension garden hose (over 15 m), the supply flow rate may be insufficient. Use a shorter hose or connect to a tap with higher flow.
6. Reconnect everything and retest.