Greeting:
I am a newbie here. Good site here too.
I replaced my daughter's hot tub pump for a Chriistmas present but the heater burner wont fire up now. I'll find that problem as soon as the temp and wind chill factor gets more favorable.
The Jandy web site says -do not operate the water heater if the outside temp is below 20 degress.
I would like to know - why not?

Post the link that says this...

http://www.jandy.com/html/productsupport/#manuals
LG manual page 24

Sounds like what I like to call a design quirk. My guess would be that at 20 degrees, operating the heater causes condensation to form on the outside of the heat exchanger. Condensation is VERY acidic and would corrode not only the heat exchanger, but also the burner tray if dripped onto it.

Some years ago (it's been a while since we used this brand of heater), they use to say you couldn't use the heater if the water was below 60 degrees.... same condensation problem.....

LG water heater.
I said this is a spa but it may be called a hot tub and it’s outside on thier deck. It's used year round for ten years already and they have to heat the water a little and circulate it to keep anything from freezing up. That means at 20 degrees (outside air temperature) the heater may have to come on to keep the water above freezing.
It could be that the gas heat venting, which hits the top vent cover directly, may condense enough moisture from combustion fumes to cause that acidic fallout into the unit. Jandy doesn't say why not. The warning was to protect the Mfg. because something may happen. What may happen? I just want to know. Maybe something in there won’t work right at 20 degrees or less and can cause a more serious problem like the gas valve freezing up in the on condition. I think it is an interesting subject tho I will be likely not be exposed to other spa repairs. Someone may have had a problem with this. Come on down!