Mystery fluid in bilge

[KWKloeber]

The above also doesn't work if you heat up the water tank.  The expansion of the hot water will also increase pressure.  As the tank cools, it will reduce the pressure and thus when the water pump is switched back on, it will run to replace the missing pressure.

Alex

As with everything boating, I'd say, "It depends."

The pressure switch is on the cold water pump not on the hot water supply side of the system.

So, if the csupply to the WH tank is X psi (same as in the cold water side) and the hot water pressure is X+temp_rise psi, the pressure pump sensor doesn't see that increase - it only knows whats on the cold water side of the equation.

So likewise if the WH tank cools down and the temp is anything above the temp of the cold water supply to it, then the pressure pump doesn't see the pressure decrease in the WH tank.  There's no reason I see that the WH would cool down below the cold side, so the WH should always be at or higher than the psi in the cold side.

At least that's my theory of how it *should* work overnight. Correct my thinking if it's flawed!

The "it depends" being that the checkvalve on the cold water supply hose to the WH tank is not leaking.

[Ron Hill]

Guys : I NEVER turn OFF the water pressure switch and I've NEVER heard the pump kick in when I turn on the battery selector switch ON!! That's over MANY years!!   

A thought

[Jim Hardesty]

Guys : I NEVER turn OFF the water pressure switch and I've NEVER heard the pump kick in when I turn on the battery selector switch!! That's over MANY years!!   

A thought

Neither do I.  Unless there's a leak.
Jim

[robbjd]

Different strokes for different boats! Our battery switch used to always stay on due to its solar wiring. Two days before we took possession of our boat the previous owner had graciously washed down the boat with its washdown system which draws from the water in which it floats.

He hadn't switched the pump off and didn't shut the cockpit shower taps off tightly enough before storing the shower head in its compartment. After driving 4 hours to move into our beautiful boat we opened the companionway to see the boards above the bilge floating, and the bilge pump almost keeping up.
The solar isn't wired that way now but I always shut off all switches, except the bilge pump three way which is always powered.