We bought a house with a Rinnai RUC98 tankless hot water heater already installed. We didn't notice anything about the water at first except only that when we did laundry, the dried clothes smelled fine UNTIL we wore them and sweat a little. The sweat releases this smell from our clean clothes that I don't really know how to describe. A lot of on-line description say it's a "rotten egg" or sulfur smell but I'm not sure if that's correct. It's just a damp, stinky, wet-dog odor. So clothes smell if you sweat even a little bit, towels go smelly in 2-3 showers (we're not a hotel and don't wash our towels after every shower) as they are hung up to dry, bath and kitchen hand towels start to smell in the same way. The only inconsistency was that our teenage daughter's clothes didn't "smell". After much confusion and investigation, I learned that my wife and I were doing our laundry in hot/warm water whereas she was doing her loads in cold water. So the city water coming into our house is fine and the culprit seems to be the hot water heater!
But what's causing the hot water to make our clothes smell, make our hair and skin smell after showers (to the point that we need to rinse ourselves with cold water before exiting the shower)? Washing our laundry only in cold water has solved the smelly clothes issue (before we discovered it was the hot water, we even replaced the very old washer and dryer with brand new ones). But warm showers (can't always rinse in cold water because we live in Minnesota winters half the year) still transfer the smell into our towels. By itself, hot water from the tap put into a glass does not smell (at least to my nose, I can't smell anything at all).
Has anyone had this problem with your tankless water heater? Some research on-line pointed to a lot of information on sulfate-reducing bacteria (SRB) that are common in tank water heaters with anodes but not much on tankless water heaters. Can SRB also live and grow in tankless water heaters without anodes? If so, how can I safely get rid of the bacteria? Should I just flush the system with distilled vinegar/commercial descaling chemical as part of the regular maintenance process and hope the smell goes away? Call a professional plumber? Help. Thank you.