The *&^%$ takagi tk3 water heater wouldn't start again this morning in redding, ca. The outside
air temp was 41 degrees, and the infrared thermometer (auto shop tool) said the propane pipe was
at 31 degrees and the h20 pipe was at 35 degrees. No fire at all, and propane this cold probably
wont burn well at all, no matter how big the tank or pipes are. I noticed this cold propane
problem as a young marine in the snow at high altitude on maneuvers. I don't think propane
has changed much in the ensuing 40 years, so before you crush that *&^%$ tankless unit, get
or borrow an infrared thermometer and see just how cold the h20 and gas inlets really are!
I never could light really cold propane. There is probably some special fix i am clueless about.
Temps at high altitude tend to be a heluva lot colder than 31F. Frost on the propane line isn't usually a problem (but with butane it could be.) Don't blame the fuel- they use propane as heating fuel with above-ground tanks in places with design temps in the negative teens, and you BET the tank temps are well below 31F!
Careful about looking at pipes with infra-red- the emissivity of bare metals can be quite different from the IR thermometer's presumption. It'll read significantly on the low side for any shiny bare metal.