Please bare with the longish explanation because I want to make sure I detail my issue properly. Brief TL;DR, at the end of the heating cycle, my pump turns on and will not shut off on its own, pulling water into the boiler, causing the steam pressure to skyrocket and water to run into the drip tray.

Long version: I recently had issues where everything else heated up normally, the pump worked as it should, but the steam pressure would rise beyond a measurable level, causing a high pitched whistling and steam to come from the safety valve. I assumed this was a temperature issue so I removed my temperature sensor probe, cleaned a thin layer of film off of it, and reinstalled it. Immediately following, the machine heated up perfectly, so I did routine maintenance with a Cafiza back flush sequence, then turned my machine off.

Due to the film, I was concerned about my water I was using. I had been using 3rd wave packets with distilled water. I bought a TDS meter and checked to find it at 150ppm. I made a new batch of water with a PPM of 70 and filled the tank... I'm not sure if it is important to note that I have the included lelit water filter attached to the intake at the base of the water tank.

The next time I turned it on (and the time after as well), the machine will heat up normally. This often includes mid-cycle the pump turning on, the brew pressure rising, and a few drops of water going into the drip tray, then heating the rest of the way, as it normally has for a year. No problem.

At about 18-20 minutes in, near the end of the heating cycle, the pump kicks on, but doesn't shut off. It will run for about 30 seconds and during this time a lot of water enters and runs into the drip tray from the safety valve. Then about 30 seconds in, the steam pressure goes from 2 bars, and skyrockets to the maximum reading. The pump continues to run, and water continues to flow into the drip tray. I immediately turn the machine off both times because I don't want to inadvertently damage the machine (any more than it might be) by letting it run at this pressure.

I am not sure if the issue is the temperature sensing probe, the water level probe, the Gicar box, my pump (hope not), or possibly my water having too low of a TDS and that triggers the refill mechanism even though the water level isn't actually low. I just don't know why that would only happen at the end of the heating cycle and not before.

Honestly, I only have a limited knowledge of these machines and am at a loss. Any and all help would be immensely appreciated. I have included a 5 second clip of what happens as well. Thank you all for the help.

[youtube]http://www.youtube.com/shorts/fkhPxcuhf-E?feature=share[/youtube]

Definite boiler over-fill issue. Interesting that it doesn't occur until the water reaches boiling temp...

Step one is clean the probe again, but then try running the machine on a batch of your 70PPM water without the resin filter on the hose. It's possible that your resin filter is actually doing enough that it is making the water too pure for the boiler-fill probe to easily sense it.
If the pump is running while it's blowing over the safety, then it's almost certainly a boiler-fill probe issue, not a temp-probe issue.