Rinnai RUR199IN Cold Water Intermittently

Kreinhagens

I've had my Rinnai RUR199in for 6 years with this ongoing problem for the last three years. The heater would perform ok for periods then not too well for periods with the chief complaint being not as hot of water as before and intermittent cold slugs of water. The heater would fire, run for a minute or so then shut off the flame injecting cold water into the line for about 15 seconds. Then refire and work for a minute or two then off again. I do religious maintenance on the unit and was not getting any error codes. I did extensive research and couldn't get any answers except that the air filter may be clogged or the flame sensor going bad. Then I hit someone's post (I can't give credit because I didn't get the poster's name) who was experiencing the exact same thing. He had replaced the thermistors, mother board, flame sensor and was just about to purchase a new unit and keep his existing one for parts. Someone suggested that his problem was with the water by-pass valve. Since it is a $49 part he opted one last try. It worked. I, being the savvy guy I am, took the low baller's route and tried the by-pass valve fix first. IT WORKED. This thing works like a brand new unit again for $49. Hopefully if anyone else is having this issue they can read his or my post and save themselves a lot of money and headaches.

BTW, when I removed the by-pass valve, it was stuck in the partial open position allowing a cold water mix all the time. The complete removal and replacement took me less than 20 minutes. Good luck.

-BK