Problem with neutralizer backwash cycle causing water overflow and spillage
I had a neutralizer and softening system professionally installed in my basement a year ago to counter the effects of my acidic well water. The system drains into my main drainage pipes, which go out to my septic tank.
Things appeared fine until about a month ago, when I noticed that during the end of the backwash cycle (last 5 minutes or so of the ~27 minutes total), water started to gush from the pipe hole that appears to be designed to deal with overflow, and did not stop until the cycle ended.
I had the installers come out last month and look at it. When they manually ran the cycle, the problem didn't happen. As near as I could tell, for a few weeks this continued to be the case, but just this last week, the last two times it's done the backwash cycle, the flooding and spillage occurred.
The timer that kicks off the backwash appears to be a Fleck 2510.
The guy who originally looked at it last month surmised there was some kind of blockage that had since cleared itself. He feels since the flooding happens at the end of the cycle, any blockage must be far along the pipe, or perhaps an issue with my septic tank. The tank was actually replaced under four years ago when we bought the house, and there's only two us living here, so I can't imagine the tank is completely gunked up. Everything's been fine for a year, so my assumption is the tank is big enough to handle the backwash cycle.
It's been quite cold here in New England lately...for all I know something is frozen outside and causing the septic tank to be prematurely filled, and that's why when the system runs at midnight, I'm seeing an issue, but when the guy tested it during the day, it was fine (but I'm really grasping at straws here, and have no evidence whatsoever to support such a hypothesis).
My concern is how to go about troubleshooting this issue. Right now the installers plan to come out on February 7 to look at it again, and suggested if the problem persists in the meantime, to unplug the unit until then.
I'm out of my league with this stuff. Any thoughts and advice would be greatly appreciated. Thanks so much,