I have a Takagi T-K1S that was installed in 2005 when our house was built. When it works reliably (less and less lately) we have been very happy with it. I haven't had much luck making it fail consistently, but it will now frequently stop heating and throw the blinking LED code of 4 flashes. According to the manual this indicates a FAN or PRESSURE SWITCH problem. (I don't have the remote control which I understand gives more specific error information).
After several discussions with the Takagi they convinced me the problem was a dirty burner/heat exchanger. They provided a detailed cleaning procedure -- which is quite involved, but I was able to complete. There was VERY little evidence of dirt/fouling on either the HX or burner upon dis-assembly. Unfortunately the cleaning procedure doesn't seem to have helped the hot water drop out problem. I got a 4 flash code again today during a shower. I will talk to Takagi again next week ... but was wondering if anyone here had other ideas.
Other facts that could be relevant. 1). The problem seems to be more frequent in colder months (colder air temps and incoming water temps) -- but it really doesn't get too cold in Florida. 2). The problem seems to be somewhat better with the outlet temp set to 122F vs 140F (although this makes the available shower temperature in the back of the house marginal due to piping temp losses). 3). I have not seen any other failure codes 4). The unit is installed in the garage, a clean environment and vented thru the side wall (total vent length ~15 inches) 5). NG supply seems correct (3/4"piping and a short run to the meter directly outside the garage wall) 6). I have a functioning water softener upstream of the heater 7). Cleaning the incoming water screen (filter) doesn't help 8). No evidence of any flame sensor or ignition difficulties
Any thoughts or suggestions appreciated.