I have a 1999 rexhall 32 ft rexaire. While camping last weekend, a secutity person informed me I had a water leak ( california drought). At night couldn't find source, turned off water till morning. It seems there's no check valve where the fresh water goes into the holding tank.In checking around , talking to a M/H mechanic familiar with rexhall. They never installed a check valve at that point. Never got an answer to why this would start now. Have had M/H almost two years, no problems of this sort before. IE: The leak occurs when the fresh water tank is full, and leaks out the overflow valve.Sorry I'm so long winded and I will appreciate all your help. THANK YOU.

Many MHs have that same leak. Turn off the RV park water for a day or so and use the tank water. I never fill my on board fresh water tank until I am ready to leave. Are you sure it was your fresh water overflow? My A/C in the rear of the MH leaves a puddle in about the same area.

No check valve on the fresh water fill for the supply tank?Ok, first a question.. On most RV's that have a hose connection you can fill the fresh tank from the hose connection is the standard city water connection and that is checked.. The other connection is a gravity feed meaning it is ABOVE the top of the tank and it is not checked, it is also like 1.25 inches diamater (swimming pool vacuum hose size). Does your RV have a SEPERATE fill fitting? Or are you talking about the flush fitting for the black tanks?That one should have a vacuum breaker, well above the tank (often in the bathroom) and fresh water (only) will leak back when you disconnect. However only what is in the line up to the vacuum breaker.. From there on it's checked.If you have like a Tornado.. then there is a spring check in the tornado, but the supply line may leak back and due to the design of the line this may be slower.I have the tornado, but fed by the original vaccum broke line so,, Well, it's complex. (I like complex sometimes,, And the hose I feed it with has a second spring check and a second vacuum breaker,, Belt and suspenders yes. Effective yes. I'm not paranoid, Germs are out to get me... And you.. And everyone else.

If you are talking about the Gravity fill and then the small hose vent for that. The odds are you are siphoning the water out of the tank. some tanks do not have an adequate air intake and with no air in the tank you will gravity siphon the water out. Doug

Reduce the level in the tank. Once it starts, it's like a siphon.

Let's see if I've got this right. You are hooked up to city water and your water tank has filled itself and is now overflowing. Is this correct?If this is what is happening the most like cause is the check valve in the water pump. Lot's of things can cause this to happen - incoming water pressure is high and is forcing water past the valve, a bit of dirt has caused the valve to stick open, or maybe the valve has just worn out. Fixes are relatively simple - add a check valve between the tank and the pump inlet, rebuild the pump, or replace the pump.

check valve!! | Good Sam Community

RayChez
Explorer
Aug 07, 2015
imgoin4it wrote:
If that valve that switches from "tank fill" to "city pressure" pressurizing the" coach it will also continue to fill/ overfill the fresh water tank.

This is not correct. Most coaches including mine has a ball valve that you can switch from filling tank or direct from the Resort park water. If the valve is working like it should when in park city water, no water should be going into that water tank. It is direct to the faucets inside the coach.

This ball valve is located on the manifold where there are around twenty other valves located for individual line selection.

But IF you do overfill your water tank and lets say that your coach is not leveled correct, it could cause water to leak through the over flow.
Dutch_12078
Explorer II
Aug 07, 2015
To perhaps make things a bit clearer, here's the previous drawing with the city water fill valve added:
10forty2
Explorer
Aug 07, 2015
Raist11 wrote:
This one confuses me. Perhaps I'm stating the obvious. Is my 1990 Triple E the only one with a valve to switch from Tank Fill to City Water? If I leave it on Tank Fill, then the fresh water tank will overflow eventually and dump out the overflow spout on the passenger side. If I have it on City Water it won't, since it's diverted straight to the lines rather than the fresh water tank.

That's the way mine is plumbed too. I have a manual quarter-turn valve that either allows me to fill the tank or to put city water to the lines. Unless the water gets past the manual valve when it's on city water setting, (in which case the valve itself would be bad), then there's no way it can fill the fresh tank. I assume the OP's plumbing is different.

**EDIT** Nevermind, I just saw the logic of the backflow valve in the water pump..... :S
BigSkyBob
Explorer
Aug 07, 2015
Old-Biscuit wrote:
luvlabs wrote:
Let's see if I've got this right. You are hooked up to city water and your water tank has filled itself and is now overflowing. Is this correct?

If this is what is happening the most like cause is the check valve in the water pump. Lot's of things can cause this to happen - incoming water pressure is high and is forcing water past the valve, a bit of dirt has caused the valve to stick open, or maybe the valve has just worn out. Fixes are relatively simple - add a check valve between the tank and the pump inlet, rebuild the pump, or replace the pump.

Ding, ding, ding........

Pump has an internal check valve and city water connection has a check

valve. They are there so city water doesn't backflow thru pump and fill/overflow fresh water tank and so pump when running doesn't leak out city water connection.......both feed same plumbing system

Simple/basic RV plumbing system

I had the same issue so replaced the fresh water pump. Problem solved.
PastorCharlie
Explorer
Aug 07, 2015
Om my Newmar there is a manual switch valve that bypasses the pump and check valve and fills the fresh tank directly from the city connection. By moving the lever from tank to city determines the use.
Dutch_12078
Explorer II
Aug 07, 2015
lfeather wrote:
luvlabs wrote:
Let's see if I've got this right. You are hooked up to city water and your water tank has filled itself and is now overflowing. Is this correct?

If this is what is happening the most like cause is the check valve in the water pump. Lot's of things can cause this to happen - incoming water pressure is high and is forcing water past the valve, a bit of dirt has caused the valve to stick open, or maybe the valve has just worn out. Fixes are relatively simple - add a check valve between the tank and the pump inlet, rebuild the pump, or replace the pump.

Ditto the water pump. I had the same problem and replacing the water pump fixed it.

For the common Shurflo RV pumps at least, replacement isn't necessary to cure the backfeed problem. Parts kits are readily available ranging from a replacement diaphragm to the complete pump head less the motor, all for less cost than a complete pump.
lfeather
Explorer
Aug 07, 2015
luvlabs wrote:
Let's see if I've got this right. You are hooked up to city water and your water tank has filled itself and is now overflowing. Is this correct?

If this is what is happening the most like cause is the check valve in the water pump. Lot's of things can cause this to happen - incoming water pressure is high and is forcing water past the valve, a bit of dirt has caused the valve to stick open, or maybe the valve has just worn out. Fixes are relatively simple - add a check valve between the tank and the pump inlet, rebuild the pump, or replace the pump.

Ditto the water pump. I had the same problem and replacing the water pump fixed it.
Old-Biscuit
Explorer III
Aug 07, 2015
imgoin4it wrote:
If that valve that switches from "tank fill" to "city pressure" pressurizing the" coach it will also continue to fill/ overfill the fresh water tank.

Correct.......

Those RVs with a water panel with valves/switches have 2 ways of overfilling fresh water tank
Via fill valve if it leaks thru OR
VIA pumps check valve if it leaks thru

Those with only a gravity fill..........pumps check valve

Remove suction line on pump..pressurize system and check for flow back thru pump.
YES.........pump check valve. Sometimes just running pump will clear 'flapper' and let it close. Otherwise...disassemble clean or rebuild
NO........then 'fill valve' for those that have one. Rebuild/replace valve
Dutch_12078
Explorer II
Aug 07, 2015
Raist11 wrote:
Dutch_12078 wrote:
Raist11 wrote:
This one confuses me. Perhaps I'm stating the obvious. Is my 1990 Triple E the only one with a valve to switch from Tank Fill to City Water? If I leave it on Tank Fill, then the fresh water tank will overflow eventually and dump out the overflow spout on the passenger side. If I have it on City Water it won't, since it's diverted straight to the lines rather than the fresh water tank.

No, your rig is not the only one with that setup. The overfill problem arises though, when the check valve associated with the water pump fails, allowing city water to backfeed to the tank through the pump. Your "City/Fill" selector valve just bypasses the pump/check valve arrangement to fill the tank. I have the same setup.

Okay, yeah that makes sense. So set to City Water, the water can still get from the lines back to the pump. Then if the check valve fails it fills the tanks more. Obviously I didn't look at it that way. Thanks for clarifying that for me.

Yep, that's the way it works. Or doesn't sometimes... :W :B
Raist11
Explorer
Aug 06, 2015
Dutch_12078 wrote:
Raist11 wrote:
This one confuses me. Perhaps I'm stating the obvious. Is my 1990 Triple E the only one with a valve to switch from Tank Fill to City Water? If I leave it on Tank Fill, then the fresh water tank will overflow eventually and dump out the overflow spout on the passenger side. If I have it on City Water it won't, since it's diverted straight to the lines rather than the fresh water tank.

No, your rig is not the only one with that setup. The overfill problem arises though, when the check valve associated with the water pump fails, allowing city water to backfeed to the tank through the pump. Your "City/Fill" selector valve just bypasses the pump/check valve arrangement to fill the tank. I have the same setup.

Okay, yeah that makes sense. So set to City Water, the water can still get from the lines back to the pump. Then if the check valve fails it fills the tanks more. Obviously I didn't look at it that way. Thanks for clarifying that for me.

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