My fresh water tank was full, 40 gal??

LEWR · 02-02-2021, 09:13 AM

I recently blew out my lines for the winter, drained the hot water htr., opened the hot & cold low point water lines. I also opened the fresh water drain. It must have been full, 40 gal. It took forever to drain. My Question is: I did not fill the tank, how did it get full? I have been towing the weight of 40 gallons of water for I don't know how long.

**LJAZ** · 02-03-2021, 07:52 AM

The only way I can think of that this could happen is that you were hooked to city water and the check valve failed. This would allow city water to backflow through the water pump and into the tank.

LEWR · 02-04-2021, 08:00 AM

Thanks, I will check that valve. Is it close to the 12 volt water pump?

JimboFunFinder · 02-05-2021, 12:06 AM

Quote:

Originally Posted by LEWR

Thanks, I will check that valve. Is it close to the 12 volt water pump?

As I understand it the primary check valve is part on the hose connection port on the side of the trailer.
Mine has failed a couple of times and also the check valves which are integral to the diaphragm water pump opened and did not stop the reverse flow through the pump which was off. My tank overflowed a couple of times.

I added a check valve in series with the water pump and it has never backflowed into the fresh water tank again.

NorthPuffin · 02-07-2021, 06:58 PM

If the check valve failed, wouldn't the tank overflow since nothing else would stop the incoming water?

JimboFunFinder · 02-07-2021, 07:59 PM

Quote:

Originally Posted by NorthPuffin

If the check valve failed, wouldn't the tank overflow since nothing else would stop the incoming water?

Yes, but it takes time as they usually do not totally blow out. When I was along the Oregon Coast comes to mind. We were connected to water and it took a couple of days for the tank to start spilling out the hose fill entry. I usually keep some water in the tank just for emergencies, so it may have taken 48 hours to fill the 15-20 gallons of water to overflow the tank. That is a reasonably small leak. My additional check valve at the pump is just belt and suspenders.
And yes, I have a pressure regulator right at the hose connection to the trailer.

**LJAZ** · 02-08-2021, 07:55 AM

Quote:

Originally Posted by LEWR

Thanks, I will check that valve. Is it close to the 12 volt water pump?

On my trailer it was right next to the pump maybe a foot or so away. Although some pumps do have the check valve integrated into the pump.

Eagle · 02-08-2021, 10:03 PM

Quote:

Originally Posted by LEWR

I recently blew out my lines for the winter, drained the hot water htr., opened the hot & cold low point water lines. I also opened the fresh water drain. It must have been full, 40 gal. It took forever to drain. My Question is: I did not fill the tank, how did it get full? I have been towing the weight of 40 gallons of water for I don't know how long.

Recently ?? And posted above on 02/02/21? Where are you located?

Here - everyone winterized in the fall .. like September/October.

Yesterday morning it was 18 degrees below zero here.