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Old 01-16-2022, 10:43 AM   #1
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M.O.C. #30025
NEWBIE!!HELP!! Fresh Water Tank overflowing

2008 Montana 3400RL. I am attached to the city water value(see attached) and I have the button pointing towards the normal flow, however the water appears to be filling my fresh water tank and then over flowing out of the back fill cap for fresh water tank and onto the ground. I bought a regulator thinking it may help but haven't gotten it yet. Wondering if I blew out a valve somewhere causing the water to go into the fresh water tank and overflow instead of directly to my water source inside the trailer.
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Old 01-16-2022, 10:50 AM   #2
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It is probably mislabeled. Try the opposite position. if water is flowing to tank you should be able to hear it. If not it is supplying sinks showers etc.
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Old 01-16-2022, 12:11 PM   #3
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M.O.C. #13740
It could also be that the check valve on the 12vdc water pump has grit in it or has failed and this would allow city water through the pump to the water tank even with the switch working correctly. John
2012 F350 6.7 L dually, 2013 3800RE with 6 pt leveling, Sumitomo 17.5" load range h tires, Samsung 18 cu ft residential fridge, 8k Morryde I.S. with disc brakes. Full timing since 2012.
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Old 01-16-2022, 01:41 PM   #4
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when i flip valve to fill tank it really flows out the back and yes you hear it flowing.
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Old 01-16-2022, 09:25 PM   #5
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M.O.C. #20477

Replace the water pump. Easy job. This is a common failure.
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Old 01-18-2022, 07:28 PM   #6
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Check the tank fill valve, there is a rubber washer in the valve that might have worn out
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Old 01-26-2022, 04:58 PM   #7
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Another problem could be your water pump. the pump has a backflow preventer that block city water from entering the tank when you're on city water. I've seen it happen!
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Old 01-27-2022, 11:54 PM   #8
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M.O.C. #18958
I have a 2007 with the same convenience panel
And have recently had the same problem
The fill selector valve had failed
And caused water to slowly overfill the tank and overflow.
The internal valve seal of the selector balve had failed
In my case it was not the pump
But a 10 dollar valve
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Old 01-28-2022, 09:38 AM   #9
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This happens quite frequently.
Most RVs have blamed it on the Anderson valve. However as stated earlier the check valve on the water pump does get dirt or does fail, allowing water to pass through and filling the fresh water tank. A simple fix is to add a check valve prior to the water pump to prevent the fresh water from flowing backwards.
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