Pressure water system confusion

[T4Liberty]

What am I missing?

I am overdue installing a new hot water heater on the boat to replace the leaking one that I removed when I bought the boat several months ago.
The new heater has been sitting in its box waiting for me to get around to it.
While getting it ready for installation, I noticed something that has me puzzled.

I have the cold water supply that went to the old heater blocked off. I can follow it directly to the fresh water pump. I have the old hot water line still open. The hw heater will reconnect to it.
While looking at it and figuring out what fittings I needed, my nephew turned on the cold water in the master head...and water started pumping out from the hot water line. I can't see (at least in the engine room where the fresh water pump and hw heater is) anywhere that the hw and cw lines are connected, like through a manifold.

So, what am I missing? Is a pressurized water system supposed to pump water into and through hw lines before towards a hw heater?

I will note, there isn't a great deal of pressure coming through. It's more like squirting with each cycle of the pump.

 

[gaston]

Do you have mixer taps ?

 

[T4Liberty]

All taps have individual hot and cold, no mixers.

 

[HopCar]

I think Gaston is on the right track. I bet the hot water valve in the head is open at least a little and when you turn on the cold water some back feeds through the hot water side. If the faucet has two knobs, make sure the hot knob is closed. If it’s a lever, make sure the lever is all the way to the cold side.

 

[T4Liberty]

Gaston wins the prize. Feel like a dummy.
Thanks fellas.
Hw faucet was slightly on.

 

[tiltrider1]

There is a single handle faucet some were. Shower, kitchen, or transom are often forgotten.

 

[FF]

Water tempering or anti scald valves may have the same effect.

 

[Bacchus]

Hand held shower head w/ a shut off valve can have the same affect. Can also result in only warm water available at other locations if the main shower mixer is left on and the head valve is shut off.

 

[Larry M]

Hand held shower head w/ a shut off valve can have the same affect. Can also result in only warm water available at other locations if the main shower mixer is left on and the head valve is shut off.

I wish you had posted this a couple of weeks ago. That happened to us last week with the deck shower. We had given Holly a bath and hadn't turned the hot and cold water off at the handles (we have a garden nozzle at the end of the hose). That night when Lena was doing dishes, all we had was warm water. My first thought was the water heater had died. It took a bit to figure it out.