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Solved problems · Plumbing · Crew answer

Why does my boat's fresh water pump keep cycling?

A pressure pump that starts and stops with every tap closed is losing pressure somewhere: a leak, a dripping tap or relief valve, a leaking pump check valve or a flat accumulator.

Symptom

The fresh water pump runs in short bursts every few minutes with all taps closed, or chatters on and off rapidly while a tap is open.

Likely cause

On-demand pumps start when pressure falls and stop when it reaches the switch's cut-off. Cycling with taps closed means pressure is leaking away: a dripping tap or shower, a leaking fitting or water heater relief valve, or a worn check valve inside the pump letting water flow back. Rapid on-off cycling while water runs usually means the accumulator has lost its air charge or there's no accumulator, a restriction such as a clogged strainer, or air in the system.

Stop now if

Water is collecting in the bilge or the pump runs non-stop and the tank is draining. Turn the pump off at its breaker, find the leak, and watch the bilge. A hidden leak can empty the tank and run the battery down.

The fix, in short

  1. Look for leaks. With all taps closed, check the bilge, under sinks, at the shower and at the water heater relief valve for drips. Also check for water draining to the bilge.

  2. Isolate sections. If the system has valves, close them one at a time. If cycling stops when a section is shut off, the leak is in that section.

  3. Check the pump check valve. If cycling continues with the outlet isolated right at the pump, the pump's internal check valve or switch may be leaking. Clean or rebuild it as the pump manual describes.

  4. Check the accumulator charge. Turn the pump off and open a tap to release pressure, then check the accumulator's air charge with a tire gauge. Jabsco's accumulator ships at 10 psi and can be tuned to the pump's cut-in pressure. Water from the air valve means a failed bladder.

  5. Clean the strainer and bleed air. Clean the pump's intake strainer and run each tap until water flows without spurting.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Fresh water: Pressure water pump with pressure switch, accumulator tank, strainer, taps and water heater relief valve

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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