Rinse water back feeding into pre-soak bin

[ACS]

When rinse is in use in bay #1, and only that bay, water is coming back into the pre-soak mix bin, not into the supply barrel.
Could it be coming back through the product solenoid and the pump motor or the hydrominder? It only does it when that one bay, which is closest to the pump room, is using the high pressure rinse.
Thanks

 

[cbchevy4x4]

Failed Check Valve at the manifold for that bay.

 

[ACS]

But why am I not having the same problem in the foam brush and tire cleaner tanks?

 

[Fatboy769]

But why am I not having the same problem in the foam brush and tire cleaner tanks?

You definitely won't have an issue with the foam brush, because it's not tied into the high pressure anywhere.

Some equipment has a separate check valve for tire cleaner and presoak at the boom. If yours is like that, that's why it's just the presoak tank.
If it's just a single check valve for both functions, the presoak is just the path of least resistance.

 

[ACS]

It’s an older car wash we bought less than a year ago with some sketchy plumbing, etc., so I can’t just compare it to the other pump stands because they’re all plumbed differently.
I think you guys have pinpointed the problem for me. Thanks!