Eric, I'm properly reading this wrong but a R 25 SC regardless of hours should have had several major services done to the engine in the last 5 years assuming it is a 2016 which I believe is the last year of production. Hour are for cruisers that put 100 + hours on their boats a year. Seasons are for those that put low hours on their boats. Regardless of hours fuel filters, oil and filter changes and anti freeze changes, belt inspections, water pump impeller and the many other preventative items should have been inspected to preserve the integrity of the equipment.
There are many gremlins that can cause the alarm. I would first rule out the obvious. Remove the filter and inspect it for contamination. That alarm is for a reason. It alerts the captain that there may be water in the fuel system and if not checked that water can do severe damage to the fuel system injector pump and injectors. The ok button tells the ECU that you know of the issue and will check it out.
Fuel systems in a diesel powered boat are easy to maintain but must be maintained. Diesel fuel over a period of time can go bad and moisture can easily be present in a tank that has minimal use. Fuel filter regardless of hour need to be inspected. I believe inspected more with less use.
Hours and years for maintenance get confused by many boaters. I enjoy reading post from Tony Athens owner of Seaboard Marine. He refers to this as Marine age. Example a 20 year old marine engine that is just coming up on 1000 hrs. The boat owner has never done a 1000 hrs service because it didn't have 1000 hrs on it. Right or wrong ? Wrong !!! The manufactures state in their maintenance manual every 100 hours or once a season, 200 hours every two years , 300 hours or every three years ........ The owner of the 20 year old boat should have done the 1000 hour inspection 4 times in that 20 years.
Sorry for the rant but if an alarm goes off and the engine runs fine don't pass it off as what could be wrong. My answer is check the fuel filters Primary and secondary that should have been changed in the last 12 months. After checking the filter and determining it clean install a new filter anyway $$$, yes but that is the cost of boating. If the issue comes back replace the water sensor on the bottom secondary filter. The sensors have been known to have Kremlins. If the issue comes back fill the tank but do not add an additive. Run that tank out. Refill and start using an additive again. I would assume a 5 + year old boat with only 120 hrs has add a lot of fuel additives to maintain the integrity of the fuel. It has not had many trips to the fuel dock in 5 years.
Good luck with your troubleshooting Eric.
