Just wondering how do you insure the water in the pumps, heaters, and adjacent plumbing does not freeze in extreme cold temperatures. Do people suppliment insulation around the mechanical compartment that is typically not insulated. It seems that it is possible for this to occur if the main body of water does not require heating for a long time - such as if the water temp is high and the setting is lowered. I think 10 hours before a filtration cycle kicks in may be enough for some ice to form. But, history and real life experience seems to indicate that this does not happen much.
Also, 24hr circ pumps will not help if they do not move water thru all of the more exposed plumbing paths.