What is a backup valve - Polaris 380 In Ground Pool Cleaner

I would ask the manufacturer not online odd jobbers.

Do you have a Back Up Valve?
It will be about 3' away from the unit.
if you do, then backup valve has failed, needs replacement.
Or... You can just replace the internal gear assembly.
It looks like this, follow the link...
Amazon com Pentair backup valve

It is likely a coincidence but you may have a restriction of the water downstream from the device. This would cause a higher pressure and might therefore add to the stress on the backup device. Regardless of the cause you still need to new backup valve or a new part to replace the part that split. They are not hard to replace if you can get it apart.

If you have trouble getting it apart you can bring it down to Leslies Pool Supplies and they can put it back in order for just the price of parts.

I hope this helps.

I think it is a coincidence. On the other hand, there could be a restriction downstream causing the pressure to be too high. I would check for this but either way you will need to buy a new one. I hope this helps.

Either you have an air pocket in the cleaner,or your backup valve is bad.The backup valve is the baseball sized unit on the hose going to the cleaner.

The backup valve is the white plastic unit in the hose that looks like an acorn. There is no adjustment to control if or when it backs up. this is all done through predetermined timing in a set of gears. If the unit is stuck backing up, you probably just need to replace the backup valve. You can take the old one apart, but this can be very hard to sometimes, and you may damage it trying. sometimes a piece of debris can cause the gears to stick, and there is a small gear that sometimes actually comes lose. But aside from that it'll need to be replaced.

You might want to pull the drive wheels and see if their might be a small pebel stuck in the drive gears on the wheel.

The backup valve should shut off completely. All the pressure should be going to the Polaris for 3 minutes, and then all the pressure to the backup valve for 35 seconds. If water is coming out of the backup valve when it should be off, then needed pressure to the Polaris is being wasted.

If the Polaris is working fine, then no reason to fool with it. If not, you need to fix the backup unit. You can open it up and clean out debris and readjust it. (You'll really need a "strap wrench" from a hardware store to get off the outer ring. I paid $6). You can purchase the the inside mechanism if you can't fix it. You can also purchase an entire backup valve...outer case and inner mechanism. I bought one for $42 off ebay but they sell for $50-60 and my local pool store quoted $100.

This sounds like your backup valve is not closing properly, so the part of drainage water comes back into your dishwasher. You can verify this by disconnecting the drain hose from your kitchen sink drain and pouring water into it. If some of it comes into your dishwasher, the check valve (backup valve) must be replaced.