No hot water when water pump is on.

Sounds like your water heater bypass valves may not be set correctly. If you have 3 valves, the 2 in the pipes into the heater should be on, the one between the hot and cold water pipes should be off.

Did you relief the pressure at the top of the water heater? Sometimes that may be a problem ? MAKE sure it is cold, life the releif valve at the top with your water pump going , you may get some bubbles and finnaly water.
Good luck
Chuck

RV water heaters by design have an 'air pocket' in top of water heater tank. The air pocket allows for expansion of water when heater without a big increase in pressure. Air can be compressed/water won't.



Getting cold water from hot side of faucet.........water heater 'bypass' valve is still open.

3 valve system......bypass is one on red/blue line


2 valve system......bypass position shown (valve handles pointing in direction of flow)


Different 2 valve system.....bypass is one on red/blue line


1 valve system......bypass would be if valve handle was pointing up



Check the backside of YOUR water heater.
Cold water should go in bottom and hot water out top.
No flow between cold/hot on connecting line (bypass line)

OPEN Cold inlet and Hot outlet (if you have a hot outlet valve and not just a check valve)
CLOSE bypass

Nice simple and clear explanation Old-Biscuit.

:)

Using logical thinking,....if the water in the tank is hot, then it is impossible for anything but hot water to come out of the hot water faucet, un less the cold water pipe is connected to the hot water pipe somewhere.
And I don't see where having the pump on or off would have anything to do w/ that.

Try draining the water heater then refilling to rest abolish the air pocket in top of tank...

Thanks for the responses, I did try lifting the valve pressure, but it was with the pump off. I will try all the above starting with the bypass valve next weekend when I return to the camper. Kind of annoying having to have people stand next to the pump switch while you take a hot shower. Especially if they wander off right in the middle of the shower.

ken white wrote:
Nice simple and clear explanation Old-Biscuit.

:)

Agreed!

If you have an outside shower ("dog wash"), make sure both valves are turned off, not just the control on the shower head. As with an incorrect bypass setting, the open faucets can allow cold water to run into the hot line when the higher cold pressure with the pump on over powers the hot pressure. With the pump off, the lower pressure may allow the system to work near normally.

Water pump ON...cold water flows thru water heater bypass closing the check valve in hot outlet nipple on tank.
Turn water pump OFF.hot water flows out of water heater tank due to higher pressure in water heater from heating the water

Close the WH bypass.

Outside shower being turned off at handle vs closing cold/hot knobs will mix the water...but typically you end up with warm water which gets colder vs hot or cold.