Sujet : Propane tankless water heater issues (gas line sizing, regulator, temp
I installed a new Navien tankless water heater over a year ago, replacing an old tanked water heater. I did not upgrade the propane line at the time, but I did of course change out the fitting inside the heater to work with propane instead of NG and adjusted the DIP switches correctly, and the Navien heater worked fine for a year. However, recently I've had a sporadic issue where the heater stops outputting hot water: the burner will come on only briefly, warming the water a few degrees above ambient, before it cycles off. This repeats every 10 seconds or so. The heater doesn't display an error.
After much troubleshooting (all air and water filters are clean, no exhaust issues, flow rate sensor is clean, etc), I've come to the conclusion that it might be either the undersized propane line, the regulator, and/or the outdoor temperature. The old propane line has a section of 3/8" or 1/4" rubber tubing, which is pretty small. The regulator on the (20 lb) propane tank is old and not adjustable; when the heater is doing its problematic-cycling thing, the regulator will briefly vent, and immediately the heater's burner will go off. The heater continues to run for a few seconds, then makes a click/knock sound, stops running, then the burner cycles back on, repeat.
This behavior seems correlated with cold weather, though it doesn't even freeze in my area, and the problem isn't consistent. Sometimes it's fine for days, only to suddenly act up again. Nothing specific I do seems to fix it, but often after fiddling (unplugging heater, changing propane tank, etc), it randomly works again, but again, no specific action seems to solve the issue.
Should I change out the regulator and increase the pipe size? If so, any insight into why it worked flawlessly for a year? Any advice or info would be much appreciated!
