Odd headhunter Royal flush failure

Wonder if anyone has seen this before, it was a first for me.

twice in a year now we ve had a Royalflush failing. First time someone flushed and didn’t notice the valve didn’t close until the bowl started overflowing. Leak contained, all clean water. We replaced the little electronic timer which activates the valve and shuts it down after an adjustable delay

second time was a lot more messy as the day head started flushing on its own in the middle in night. I only realized it happened the next morning when I stepped on the aft deck of my boat and heard an Isis alarm. Turned out to be empty water tank as the head flushed about 400 gallons… filled up the holding tank, overflowed. Thank fully with clean fresh water. We spent two days removing and drying ceiling panels downstairs, drying out carpet, two mattress, and more.

aoninm trying to figure out how the head decided to just start flushing on its own. Switch looks good and headed tested just fine. Needless to say for now the fuse is pulled on that one. Going to talk to HH to see if they have an idea of how it could
Happen

to make things worst, the master head and a VIP head down below back filled with black water. A bit messy but no damage. That’s nr 2 I m trying to understand since these head have a check valve and in theory nothing should back flow. I m guessing the check valves need replacing even though they flush perfectly well.

I also don’t understand why the holding just didn’t overflow overboard since we have a 1” vent on port and stbd side, no carbon filter and apparently lower than the lower decks head

any suggestion welcome, I ll call HH tomorrow or Monday.

Yes we replace all modules and switches. I was tempted to eliminate the modules in the crew and use momentary switches but since it seems to be a rare failure I kept them stock