What you are describing
Originally Posted by GaryRat1616
After you use water, pump will continue to run, but very quiet. Does not shut off. We dont seem to have issue if fresh water tank is filled - only when it starts to empty.
To stop it, we generally run water some more until pressure drops enough to kick pump back on. Does a charge of the system, and then shuts off.
No visible leaks anywhere. Suggestions?
This is what happens when the water pump dry locks, or in other words, looses pump prime. This is what is happening, the cause and the fix.
Sunline put the suction port of many 2004 units maybe other years too, in the side of the fresh water tank. It is about 1" up from the bottom to the center of the hose that draws water up to the pump.
So, fill the fresh tank with water, turn on the pump and then it catches prime, builds pressure, makes lots of banging noise from vibrating pipes.... and then stops.
All is good until the tank starts getting close to the lower part of the fresh tank. When you approach the area of tank level that is close to the suction hose, the pump can suck air over the top of the water line, that air then creates a air pocket in the pump, the pump looses prime and will not get prime back again until you refill the tank far above the suction hole.
The pump when it looses prime like this will go to a very fine high pitch whine that is hard to hear and it pumps nothing. Running the pump a long duration of time like this will cause damage.
I learned this the hard way. We left the camper, went for a camp ground walk with the pump switch turned on. While we where gone, the system must of been on the verge of low pressure. The pump kicked in, sucked in a big air bubble over the water fill line and dry locked the pump. When we came back to the camper a few hours later I walked in and smelt hot electrical. Oh boy...
Then I heard a real fine whining. I kept hunting until I found the very low pitch came from the water pump that was so hot I could not touch it. That killed that pump to where it would no longer catch prime unless I poured water in the suction hose and quick turned it on. Note to self: Turn the pump "off" when ever leaving the camper for any length of time.
The pump priming ordeal got old quick and I bought a new variable speed pump and fixed the problem with the tank.
Your in-laws 2004 most likely has a tank with this side port. There are 2 ways to deal with this. When the tanks gets low, refill it. Yes there is still a lot of water in there, but the problem will not happen.
OR they can convert it to this. I moved the suction port out of the side of the tank to the bottom port. I can now draw the tank down to about the last quart of water. Before a good 3 to 5 gallons was left inside when the pump lost prime.
If you look on the far left of the tank you will see a brass plug in the old suction port, a good 1" above the bottom of the tank.
I added a Tee in the drain port and upgraded the take forever to drain... tank drain valve to a 1/2" boiler drain valve.
I have done this same upgrade to both of my 2004 campers. When boondocking I want to be able to use every once of water.
Hope this helps