Customer has a 6+ year old tankless unit that we installed stop working, when this occurred the unit was not giving an error code. Turned the hot water on and the unit was working perfectly, even turned the unit off and on multiple times and there were no issues. I did noticed the valve for the condensation line was closed all the way and i opened the valve a little so the condensation could exit the unit. Called Navien and had them log the concern for future reference in case the issue occurs again. No charge to the customer we were only out for a short time and no tools were involved.