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Rinnai Tankless Water Heater only putting out warm water
I have a Rinnai tankless water heater (R94LSi) that has been working perfectly for 10 years. Each year I flush the system with white vinegar as instructed in the manual. After doing some unrelated plumbing, I turned the water back on and now the Rinnai is only putting out warm water. I suspected sediment might be blocking something so I flushed out the system for several hours with vinegar. It is still only putting out warm water. The water flow through the heater is very strong. It sounds like it is running normally but then slows down as if running at a slower speed. I'd be surprised if it decided to break at the exact time that I was doing my plumbing work. Could sediment fool the flow sensor? Would that cause this problem or could it be something else? There aren't any error codes being displayed.
Thank you for your help,