City water connection filled tank

Water tank should NOT fill up when I am connected to city water--correct? I'm thinking there should be a valve in the water pump that prevents city water from going to the tank. But of course, my tank filled up and water was actually comi g out the fill cap. Can the water pumps be rebuilt or am I missing something with my thinking here?

OkeyOkins said:

Water tank should NOT fill up when I am connected to city water--correct? I'm thinking there should be a valve in the water pump that prevents city water from going to the tank. But of course, my tank filled up and water was actually comi g out the fill cap. Can the water pumps be rebuilt or am I missing something with my thinking here?

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The city water connection on the side of the trailer has a check valve in it. As soon as that check valve gets pressure from the city water side, it SHOULD block the water pump side. If that check valve is defective, it will do just as you described.

You would be correct. Here's a copy of a schematic Bill posted awhile ago. It may just be clogged or needing replacement.

So the check valve is EXTERNAL to the pump?

I forgot....... There is also a check valve at the pump. If that one fails, you will have that issue. If the one on the fill fails, you will have water passing the other way from the 12V pump. Some RVs only have the one.

I did look in plumbing and must have missed this thread.

I looked under the sink to see I could see any back flow device connected to the pump. I could not see any valve at all. there is a filter connected to the pump.

Also, the plumbing diagram does not match my 2021 TM.

Disconnect or turn off the city water supply. Turn on the pump, and let it pump a gallon or so of water out of the tank. Start-stop the flow a few times. Be snappy about it, not gentle. If there is a bit of grit in the anti-backflow device, this may flush it out.

If no help: Find the make (almost certainly ShurFlo) and Model of the pump. Then go to the mfr's web site and look up the pump. It will tell you if the pump has an integral anti-backflow device. Most do. If it does not have one, you need to look for the problem elsewhere. If it does, then you need to consider repair or replace. SurFlo has a repair kit for the pump head on many of its pumps. This is where the anti-backflow device would be located. Not expensive, and easy installation.

Bill