Hoping a professional who specializes in Rinnai tankless water heaters can help with this - we bought a house last year that has a 3'sh year Rinnai tankless water heater. We get continuous hot water most of the time, but a couple of times a week we get cold water in the middle of our showers that can last up to a few minutes (it's not just a quick jolt of cold water). We haven't done much about it, but the most recent experience lasted a few minutes while my 5 year old was shivering with soap on him :( Is there anyone who can explain what's going on and, more importantly, fix this? Thank you!!