Ten years in service as of April 1. Makes our hot water, so operates year-r ound. Not one single glitch all these 10 years, but the service manual 'sug gests' a firebox cleaning every five years or so. So, I purchased the kit ( $59) and the cleaning tool ($29) and decided that this would be a good bit of PM to do while my new hip heals as I can do it sitting down.
Kroil is wonderful stuff. From reading on-line, it seems that these beast a re notorious for seizing nuts and stripping studs. Given that, starting Sat urday afternoon, I treated all the nuts and screws lightly, once again this morning. nothing seized or stripped, everything came off clean.
The old gaskets and heat-washers were pretty much done. The cover plate nee ded a bit of cleaning, I replaced the spark ignitor (included), cleaned the heat-exchanger - got about 1/3 cup of grit - and cleaned the site-glass. C hecked the inhibitor levels (acceptable) cleaned the fire-cone, and put eve rything back together. Torqued the nuts per the sequence, fired it up, and off it went. Total time invested: about 2 hours.
I promise not to let it go 10 years, again, but this unit did not seem wors e for the wear despite all that time. Note that this unit heats (well) our entire house (4,500 s.f.), so no complaints.
Peter Wieck Melrose Park, PA