Air in Hot water lines

[PrairieBoy]

Hello Everyone
I have a seasonal site and when we leave the camper we always shut our external water source off. After a few days when we return and I turn the water back on we always have air in the hot water line/tank. I usually go to the outside kitchen and run the hot water to get all the air out and everything is good until the next time we leave and shut the water off. Lately I have been running the cold water first with no air just to verify that it is in fact a hot water issue. Hot water line always has air in it. There are no leaks of any kind in any of my taps or lines that I know of.

Trailer is a 2012 Surveyor SV-305 and this issue has been going on all summer long. My external water source is also back filling my fresh water tank (another reason why I can't leave the water turned on when we are away) so the tank always has some water in it. This would eliminate someone turning on the pump and pumping air into the system. Air is getting in somewhere, Anyone have any ideas.

Thanks
Todd

[youroo]

Check valve in F/W pump is bypassing to F/W tank. Youroo!!

[Twisty]

If the city water is back filling the tank, the water is getting past the 12 volt pump. Water seeping or leaking past the pump would/could lead to air in the water heater.
The pump has a check valve that may need to be cleaned or replaced.
If you choose not to work on the pump next time you are there, before you leave, open a hot water tap to relieve the pressure.

[PrairieBoy]

The water pump is 1 of 40 issues with this trailer. It will be going back to the dealership immediately after we pull out of our seasonal site. I don't believe this is the cause of my problem. I never have air in the cold water side, only the hot water side which tells me that the air is most likely coming from the hot water tank but how.

[Twisty]

There is air/gases mixed in with the water. There is air/gases mixed with all water everywhere.
Air and water need to expand when heated.
Cold, dense air/water enter the heater filling the space.
As the mix gets heated it expands and has one place to go - past the bad or fouled check valve. TaDa!

Edit
Hydronics is the science of heating with water. All hydronic systems require an expansion tank and an air separator.

[TURBS]

Is this a hydrant type water supply?
With a pull up lever or a turn knob shut off ?

[Herk7769]

Originally Posted by PrairieBoy

The water pump is 1 of 40 issues with this trailer. It will be going back to the dealership immediately after we pull out of our seasonal site. I don't believe this is the cause of my problem. I never have air in the cold water side, only the hot water side which tells me that the air is most likely coming from the hot water tank but how.

I respectfully disagree.


The first issue is air dissolved in the campground water in your lines that is released over time. It collects in the only place it can; your hot water tank just as Twisty said.

The second issue is related to the first. As water trapped in the lines is heated by solar radiation, it has to expand. There is no place for it to go except compressing the air space in the hot water tank. The pressure relief valve in the hot water tank would open "eventually" but your weak check valve inside your water pump fails "open" and bleeds that water pressure into your fresh water tank.

When it cools down at night, you will have a LOT of air in your hot water heater since it will be sucking air through every valve in your camper (nature abhors a vacuum). Valve seals are designed to keep water in the pipe; not so much air coming the other direction when being sucked on. (cup shaped and water pressure from under the cup keeps the seal. Air can easily flow around the collapsed cup.)

[Twisty]

Well put, Herk.

[PrairieBoy]

Thanks for the explanation. Wasn't sure if there was a problem or not. Our old 5th wheel didn't do this but the water pump was working properly on that trailer.

[PrairieBoy]

Originally Posted by f1100turbo

Is this a hydrant type water supply?
With a pull up lever or a turn knob shut off ?

It has a turn knob shut off.