Fresh water confusion

[SteveSealey]

I don’t know the answer to this and that’s why I’m asking. When connected to city water, my fresh water tank overflows. Is there a bypass valve that I’m missing. Fresh water tank is under bed in rear of motor home.

 

[Martian]

The check valve in your pump has failed and is letting city water flow into the tank. Check the website for your pump and get a replacement check valve.

 

[Jackiemac]

The check valve in your pump has failed and is letting city water flow into the tank. Check the website for your pump and get a replacement check valve.

This happened to us and we just cleaned it and it worked for another few years.

 

[Rene T]

are you new to rv’ing and is the rv new to you?
It may not be a pump check valve.
Little differently. Some rv’s have the option to fill their tank using city water by opening one valve. If you have that option, make sure the valve is shut. It will be in your water bay and will be labeled city fill or normal. It may be labeled a little different.

 

[SteveSealey]

I’m not very familiar with it. Class C . An outlet for water on the passenger side of the vehicle and outlet for city water on the driver side.

 

[CharlesinGA]

This video describes the quick fix rather well. The check valve not seating is usually caused by running the water pump when you have city water pressure on the system. What she shows you is how to get the pump's check valve to seat properly again.

 

[Kirk]

An outlet for water on the passenger side of the vehicle and outlet for city water on the driver side.

It might help if we knew what RV you have. Also, tell us how you fill the fresh water tank. If you have a connection for city water and a different place to fill the tank that you put a hose into, then it is definitely the water pump that is the problem. But you need to tell us more if we are to help.

 

[Jackiemac]

Ou

This video describes the quick fix rather well. The check valve not seating is usually caused by running the water pump when you have city water pressure on the system. What she shows you is how to get the pump's check valve to seat properly again.

Our pump was off but still overfilled the tank...

 

[CharlesinGA]

Ou

Our pump was off but still overfilled the tank...

What usually happens is you have city water hooked up, then without thinking, you reach up and flip the pump on. A moment or a bit later, you realize you don't need the pump and turn it back off. This is the point where the check valve does not seat correctly and the city water starts pushing thru to the FW tank.

Charles

 

[SteveSealey]

I have a 2017 Thor Quantum PD31. I can fill the fresh water by inserting a hose on the passenger side of the vehicle. City water inlet is on the driver side.

 

[CharlesinGA]

I don’t know the answer to this and that’s why I’m asking. When connected to city water, my fresh water tank overflows. Is there a bypass valve that I’m missing. Fresh water tank is under bed in rear of motor home.

I have a 2017 Thor Quantum PD31. I can fill the fresh water by inserting a hose on the passenger side of the vehicle. City water inlet is on the driver side.

The backfeeding of the water is happening at the water pump. City water pressurizes right back to the pump. If the check valve in the pump is seated correctly, no water will go back thru the pump to the tank. If the check valve in the pump is leaking for any reason (trash caught under it, didn't seat squarely, worn and won't seal) then water will leak thru the pump intake pipe back to the tank. As the video above notes, remove all city water pressure, open faucets to remove all pressure from the system, then run your pump with all of the faucets open. Flow a bunch of water thru the pump and check valve. If it is "trash" from the tank (shards of plastic from cutting holes in the tank at the factory, for instance) the trash may wash out of the check valve. Close the faucets and allow the pump to build pressure in the system until it turns off. Wait. If the pump does not recycle frequently, hopefully off for 15 to 30 minutes or more. then the check valve is holding pressure in the system. Turn the pump off and you can reapply city water pressure.

If the pump persists in re cycling on and off, you have leakage somewhere. First check all faucets, outdoor shower, toilet water valve, shower, etc. If you don't find any leaks external to the system, then the check valve in the pump is suspect. Some people install and inline check valve to fix the problem, others tear the pump down and install a kit in it, others replace the pump.

If you resolve the problem by simply running the pump, when done, remove your faucet aerators and see if they have trash caught in them, again, plastic shards from the hole saws used to cut openings in the water tank are the biggest problem.

Do you have a inlet screen on the pump, or near it? This should catch trash from the tank. First pic is the first inlet screen I bought. Where it stopped turning is where it stopped, upside down or sideways, I didn't like it, so I switched to a different model with a swivel fitting on it, Second pic shows it on the left side of the pump. If you have a screen (doubtful on a Thor product) then you should not be getting contamination from the tank into the pump. It could easily be the check valve simply not seating correctly, which happens from time to time.

Your problem is not unusual, there are dozens of Youtube videos on the problem with variations of the fix I described above. Try the fixes first before condemning the pump.

Charles

 

[Jackiemac]

What usually happens is you have city water hooked up, then without thinking, you reach up and flip the pump on. A moment or a bit later, you realize you don't need the pump and turn it back off. This is the point where the check valve does not seat correctly and the city water starts pushing thru to the FW tank.

Charles

Not in our case. We had turned water off outside then back in when we got home late one evening. Next morning a knock at the door from our neighbour to tell us water was pouring out. Pump hadn't been touched...

 

[CharlesinGA]

Pump diaphgrams and check valves can be replaced. Here are three and four chamber kits for certain model Shurflo pumps. Kits are fairly cheap, $20 or so and not too difficult to replace.

 

[Kirk]

Charles has given a very good answer, so no point in my repeating what he posted.

 

[Rene T]

I have a 2017 Thor Quantum PD31. I can fill the fresh water by inserting a hose on the passenger side of the vehicle. City water inlet is on the driver side.

It’s not a very old rv. Are you sure you can’t fill the tank while hooked up to city water. Look for a valve in the wet bay that would allow you to fill the tank while hooked up to city water. If you have such a valve, it could be partially open or is leaking by. Very common for people to forget to put that valve all the way to normal position. See my post #4.
Can you give us a picture of your wet bay?