Hooked up to city water it does not run through pump.
Water from fresh water tank is only water through pump.
If your traveling and your heater is on you will not need to worry your tank compartments and water pump will be heated.
Look at #5 Driving in winter weather.
Was at Newmar in Jan 2010, 1* with water in tank, than traveled to FL. and had no problems even when we had to go back to Newmar in Feb. The furnace worked flawlessly even when dry camping at the Cracker Barrels overnight.