Odd water pump behavior

DrewE - I think you have it. I've been staring at photos of the rig's plumbing compartment and (I've been) drawing diagrams. There is a single valve on the cold inlet to the tank and a check valve on the outlet. In normal mode any pressure in the hot tank will push on the cold system and any pressure lost in the tank when a tap has been opened needs to be replenished before the pump shuts off. In bypass mode, there is no air bubble in the tank to affect things.

I suppose if it really bothered me that it takes the pump a few seconds to shut off, I could add a check valve on the cold feed to the tank. It doesn't.

The hot and cold water lines are connected together through the water heater. Water normally only flows one direction, from cold through the heater to hot, but (unless you have a check valve on the water heater's inlet) it can flow in either direction if the conditions are right. Hence, the air pocket in the water heater works on both the cold and hot water sides. Usually the only time there's a check valve at the water heater is in some setups where the bypass uses one or two valves rather than the straightforward three valve bypass setup.

I suspect that if you start with the water in the heater cold, and turn on the heater and let it warm up, and then open a cold water tap, the initial burst would be at a higher pressure than usual due to the expansion of the water in the heater when heating it.

joebedford wrote:
Pump takes 3-4 seconds to shut off after closing the tap. That's pretty much normal I think.

It's not normal for any coach I've owned.

You may have had some air in the lines. Maybe the air pocket resolved when you opened the tap?

Hot water tank has the AIR POCKET to allow for increase in pressure when heating water

Cold water is static line until faucet is opened..then when closed line pressure goes up quickly....hot was still static

Swapping to bypass (water heater out of loop) both hot/cold lines are now static until faucet is opened....close faucet and line pressure increases quickly