[JandS]

Fired it up today hand tool on and starts spraying and pressure drops off...release trigger for a couple of secs and press again sprays then pressure drops off again...did this a couple more times so turned it off and on again and it did it once more then it was fine and not a problem rest of day.
This is about the 3rd occurrence so presume the pump will be wanting servicing/replacing, any ideas?

[AJB]

Sounds like air leaking into the system to me.
Try bleeding it before starting. or check the feed pipes to the pump.