Fixing RV Fresh Water Tank Overflow Valve Problems (Leaking)

Boondocking is a lot of fun but you must have a supply of fresh water on hand to enhance that fun. However, things do not always work out the way you want and sometimes your freshwater tank loses more water than it keeps.

One of the reasons why you may be getting some water leaking out of the overflow valve is that there is a continuous flow of water into the freshwater tank. The source for this is that the change-over valve may be damaged and needs to be replaced.

To learn more about fixing your RV fresh water tank when it overflows through the overflow valve, just continue to read our article. We explore the issue to help you find the sources and the solutions to this growing problem.

RV Fresh Water Tank Overflow Valve Problems


There are several sources for this problem. The first one could be that there is something wrong with the system when you use the outdoor shower. If the handles are slightly open and the showerhead is not fully depressed then there can be a little bleed between the two systems.

Double-check to make sure the outdoor shower accessories are all in their right place and that there is no bleeding taking place. If there is something out of place, then just put them back where they belong and see if that solves the problem.

A second source is having the water pump and the city water on at the same time. A third source would be not having a water pressure regulator in place when you are using city water that comes with high pressure. The final source could be that the water pump failed.

One fix for these issues is to simply cycle between the water pump and the city water option. This needs to be done a couple of times to get that problem solved. To do this cycling you have to :

- turn of the campsite water

- turn on the water pump

- run faucet for about 10 to 15 seconds

- turn off the water pump

- turn on campsite water

- turn on the faucet for about 10 to 15 seconds

- then repeat 2 to 3 times

What this process does is re-set the check valve inside your water pump. If this procedure doe not work and the problem continues there are a few things you can do:

1. Buy a rebuild kit for the water pump and make sure the check valve is user-serviceable. Not all are.

2. Add your own 1-way check valve to the water line on the inlet side of the pump

3. Replace the pump

If you are not that mechanically inclined, hire someone who is. You want the repair to be professional and good. Sometimes the RV makers may have designed the freshwater tank incorrectly and placed the overflow valve too low. When this happens you cannot fill your fresh water tank all the way.

To find the right level of water may take some trial and error before you get it right.

Why Is My Freshwater Tank Overflowing?


On top of the issues, we just mentioned there are a few other reasons why you may see a trail of water coming from underneath your RV. One owner found that his freshwater tank would overflow when his rig was not level.

He found this out just by backing into a campsite and saw the water trail from the road back to the water tank. To solve this source of leaking water, he had to re-position his RV until he was level and the water stopped flowing.

Another good reason why your water tank’s overflow valve is leaking is a manufacturer’s error. In their construction of the water tank, they simply placed the overflow valve’s opening too low on the side of the tank.

When this happens there is little you can do outside of not filling the tank to capacity or replacing the freshwater tank with a properly located overflow valve. To check to see if this is the problem, you can get a small water meter and install it on your waterline.

The digital meter will let you know at what level the water starts flowing. For example, if you have a 50-gallon freshwater tank and you start seeing a trickle of water, check the meter. If it is reading 46 then you know that you can only fill the freshwater tank to just below the 46-gallon mark.

Another source may be the O rings. That is if you own an RV with a ‘Anderson Kantleak’ valve. If you switch water sources while under pressure, the water pressure will displace or break those O-rings.

The repair is either replacing the entire unit or just the valve behind the switch. It's your choice which repair you make.

RV Fresh Water Tank Overflow Leaking


As we have said many times in previous articles on repairs, it is always best to check the simple and easy-to-reach possible sources first. Doing this can save you a little money and time as well as some embarrassment when the repairman finds an easy source for your problem.

Also, if the source is something simple and easy, then generally the repair will also be simple and easy to do. It shouldn’t cost you a lot of money to repair the problem. Plus, If these sources are not the problem, then you have eliminated them from your search and you can move on to other possible sources that are a bit more complicated and expensive to fix.

What you can do for different areas of your RV or travel trailer, etc., is create a checklist of parts that could break down or where potential problems can occur. Then use that checklist to help you find the source of the problem.

This too can save you some time and refine your search so you hit only those spots that would be the real source for the leaking. if none of those areas on your checklist is the source, you may have to go to a professional repairman and have him help you track the problem down.

Tank Overflow Design


If you are not already aware of the design, you will need to know that the overflow valve does double duty. It acts as the vent for the freshwater tank when it is not letting excess water out of the tank.

The overflow valved should also have roughly a 1 1/4 inch hose attached to it. When it is working properly, you do not want anything stored underneath this valve. Water will come out of it.

This hose should be white with a blue line on it. It should also be a little bit longer as it needs to drain out of the way of everything. One of the problems with the different hoses you find underneath your RV is that there are quite a few of them.

Along with the overflow drain hose, you will find the hot and cold low-point drain valves. The hoses attached to them are red and blue with a black colored valve at the end. Then there should be a second blue drain hose underneath your RV as well.

That extra blue hose with the white-colored valve should be the winterization hose. DO not confuse that with the overflow drain hose for your freshwater tank. On most 5th wheels, you should find the overflow drain hose on the driver’s side of the trailer.

One location is right behind the water heater. Your design may be a little different than that. But there is one design that many owners may have that cancels all this out. Some freshwater tanks do not come with an overflow drain or valve.

You should check to see if yours has one or not. There is a danger of not having one, and has been reported on at least one RV discussion forum, is that the freshwater tank could explode if overfilled.

How rare or common is this situation is not known. Some people simply get water coming back out of the intake line letting them know their tank is full. You will have to be the judge in this situation and be careful filling your freshwater tank.

How Do I Stop My Freshwater Tank From Filling Up?

Ho- D-I-Stop-My-Freshwater-Tank-From-Filling-Up

Some wise guy will probably say simply turn the water off. But that is not what is meant by this question. This situation refers to the fact that your freshwater tank fills up unexpectedly when you are hooked up to city water.

There are two sources for this problem. The first one is that someone left the quick-fill valve open and the city water is using it and filling your tank. This is not a hard problem to solve as all you have to do is close that valve.

But this valve can fail as well when in the off position. When it does, you will need to replace the valve. The second source for this problem will be the check valve that is usually an internal part of the water pump.

Its location is near the outlet side of the pump and it too can fail. This is supposed to be a rare occurrence but it does and may happen to you. Regardless of its location, it is an integral part of your water pump.

If you cannot fix the check valve, you could replace the entire water pump and solve your problem. However, you do not need to do this if the water pump is still working well. All you have to do is add an after-market check valve to the waterline.

If you cannot remove the broken check valve inside the water pump, that is okay. Just install this inline check valve to the outlet fitting of the water pump. The broken check valve should still let water flow if it is stuck in the open position.

The inline check valve will take over the duties of the broken check valve and stop water from backfilling your freshwater tank.

What To Do When The Check Valve Fails


Even though this is said to be a rare event in the life of an RV or trailer, it can and will happen from time to time. It could even happen to you and when it does you need to know your repair options.

Here are some of those options you have to choose between. Some may be expensive and not fit your traveling budget so you may want to look at the cheaper options instead.

1. Rebuild the water pump- this is something you can do and there should be kits available to make the repair a lot easier.

2. Replace the water pump- probably the simplest repair task of all. It just requires loosening and removing several bolts and taking the old pump out and putting the new one in. Don’t forget to tighten the bolts.

3. Add the check valve as explained earlier

4. Add an ordinary valve between the water pump and the tank. Another simple process that requires cutting the waterline a bit.

4. Check the city water line valve- this could have failed as well although it is rarer than the check valve. Replace it if it has.

Some Final Words

There are a lot of parts to an RV or travel trailer. Sooner or later one of them will fail. The freshwater tank and system are not immune to this fact. When it happens to you, remember to check the simple sources first.

That action may save you both time and money. Not to mention any embarrassment that may come if someone else finds the source to be simple and easy to fix.

Leave a Comment:

Add Your Reply