I recently cleaned a takagi tankless tk-3 with a vinegar solution. Now the heater does not light reliably. I can hear a solenoid of some type open and close, open and close - in rapid succession every few seconds, and sometimes the flame comes on, but I do not hear the fast clicking of the ignitor like I do I my own tk-junior. I'm wondering if cleaning the unit with vinegar may have affected a sensor internally - or maybe even damaged it. Anyone have experience with Takagi units? Fault code is 111 - poor ignition. I'll do a google search for other info out there and will return to this post with updates, as I see there is not a lot of input on this site with tankless water heaters specifically.