I used the thermo II one man for many years would hit the start of the hose at about 28c I never had problems with any thing breaking
I think 2011 was coldest down here about -9 through days still no issue that year although fan jets didn't like it much,
I used hot to keep working, to be honest I find the additives as effective as hot, ( although they don't stop it freezing ) the hotter temp has a tendancy to eat through the extreme brushes and equipment
Missed hot today but the heater seemed to work for an hour or so
Now I've got rid of it, probably means be a cold winter, haven't needed it last few years