I can only assume that something else happened when the surge damper was fitted, perhaps a pipe was rerouted that prevented it from vibrating against a wooden panel, or something like that. https://www.truma.com/uk/en/camping-guides/guide-water-pumps-for-motor-homes-and-caravans#to-502f261c-696d-4dea-8200-77d5300c745f Antifouling, Paints, Varnishes & Tools Antifouling Topside Paints Primers & Undercoat Varnishes & Wood Treatment Thinners & Cleaners Paint & Varnishing Tools More Antifouling, Paints, Varnishes & Tools Inflatable Kayaks Stand Up Paddle Board (SUP) Oars & Paddles Kayak Paddles & Accessories All Boats & Kayaks

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DC to AC Inverters Pure Sinewave Power Inverter Waeco Modified Sinewave Inverters Horns Compact Electric Horns Electric Trumpet Horns All Electrical My immediate thought was that I must have a leak somewhere caused by a frozen pipe over the winter. But I took particular care to drain the system of water using a Floe draindown attachment and also driving the vehicle around with the drain valves open for a while to release any dregs of fluid. I am pleased that fitting a surge damper has made a difference to the noise, but from what I know of the way they work, by its self it will not change the noise the pump makes but it will affect how often and for how long the pump works. If there’s no water leakage preventing the water system from pressurising properly, the prime suspect for the ‘surging’ must be the Whale Pressure Switch. So if the problem does not spontaneously cure itself, beginning by swapping the Pressure Switch would make sense. And, if there are no leaks and fitting a replacement Pressure Switch and pump is ineffective, that would just leave the Whale surge damper. Installation instructions for the damper are here Does anyone have any other suggestions of likely cause or steps I could follow to diagnose the problem more accurately.

Thanks Derek. Have saved a copy of that exploded view for future reference. Suspect this might not be the last issue I have with the pressure switch. Well I had a probe at the non-return valve with a blunt instrument a couple of times this afternoon, as Whale suggest (nothing too strong) and it made no difference. Electronic Charts Garmin BlueChart G3 Vision - Small Area Chart Garmin BlueChart G3 - Regular Area Chart Garmin BlueChart G3 Vision - Regular Area Chart Garmin BlueChart G3 Vision - Large Area Chart Garmin Navionics+ & Navionics Vision+ All Electronics I've just had another go and I've discounted a leak at the tap as it stops dripping after 30 secs or so.The non return valve fitted on the wall inlet should keep the system pressure up, even with a pin hole in the delivery hose. Fishfinders Humminbird Lowrance Garmin Fishfinders Garmin Transducers Navigation AIS Receivers Transponders