Water tank ballooning?

[Campwme]

Last night we heard very loud noise that literally rocked our 2000 Class A Dolphin National 37'. Took the flashlight looked all around, up and down, over and all. Nothing. During the night heard several loud popping noises, everything works fine. This morning when I got up put my feet on the floor I almost fell forward, thought I'd lost my balance,,hmmm. Went into bathroom came back into bedroom and literally walked uphill toward the bed! What the heck is going on? Woke up the hubby, went outside exploring in daylight, nothing looks unusual but then upon opening the very last basement doors on both sides and using a flashlight, voila! The water tank is literally ballooning and pushing up the floor! Shut the water off from outside, turned on faucets inside to let some out. Question is, will the tank go back to normal size?

[Campwme]

Update: Tank went back to it's normal size after turning off water and opening all faucets and letting gray tank flow out at same time. The "popping" sounds were the screws holding down the floor under the bed, minimal damage. Replaced check valve and all seems normal for now! Thanks for the info from all.

[Bill_Satellite]

While the tank will return to normal size, I would be very concerned about the loud bang. Something broke! The floor of your coach has also now been badly damaged if the plywood flexed as must as you have described. Check all pipes and connection anywhere near the tank outside and the plywood above the tank to see if you can access the damage. The vent, as mentioned, needs addressing as well.

[doxiemom11]

We also have had a selector not fully over to the city water position and our tank did slowly fill also. We also have had a stuttering pump when using water from the tank and the selector wasn't totally off from the city water position and onto tank. Only a small amount too.

[mccsix]

Had the same problem it was the selector valve not fully in the city water position. So it was very slowly filling the tank while providing city water pressure. My overflow worked so I didn't have the tank expansion but it sure flooded around the coach. My guess is if it didn't crack/split the tank it will be OK after it normalizes.
Got to ensure fill selector is firmly in the right position and don't trust the position markers alone.

[gutfelt]

Campwme wrote:
Last night we heard very loud noise that literally rocked our 2000 Class A Dolphin National 37'. Took the flashlight looked all around, up and down, over and all. Nothing. During the night heard several loud popping noises, everything works fine. This morning when I got up put my feet on the floor I almost fell forward, thought I'd lost my balance,,hmmm. Went into bathroom came back into bedroom and literally walked uphill toward the bed! What the heck is going on? Woke up the hubby, went outside exploring in daylight, nothing looks unusual but then upon opening the very last basement doors on both sides and using a flashlight, voila! The water tank is literally ballooning and pushing up the floor! Shut the water off from outside, turned on faucets inside to let some out. Question is, will the tank go back to normal size?

it should regain its form but never ever seen a water thank not have a overflow hose relief system and also never seen where city water flowed through a holding tank before tap deliver; mine is city or tank water on a lever if I leave it on tank the tank over fills and drains out on the ground so there something really screwed up here for sure

[SidecarFlip]

Bad check valve. I tend to valve off my FW tank when hooked to city water anyway. That way even if the check valve sticks, no enlarged tank.

[Bruce_Brown]

^^^ Hooked up wrong, I would suspect.

[2oldman]

Why is city water filling the tank?

[Bruce_Brown]

The tank will go back, why the vent/overflow didn't do its job is what needs to be addressed.

[DrewE]

Whether or not it will return to its original size and shape, I can't say. It can't hurt to try and see what happens. However, if it were me, I would also be considering how much a new tank is installed just in case.

It does sound like you have a plugged tank vent and a bad check valve in the pump or a leaky fill valve, allowing city water to pressurize the tank. You definitely need to get the vent line fixed, and probably ought to get the check valve working too.