Pumps can be a danger area as well. The friction of the mechanical shaft seal in the pump generates heat. The motor is air cooled and will not be damaged if the pump is running dry, but consider what happens to the pump assembly.

Normally, the water circulating through the pump carries away the heat generated by the pump seal. When the water stops moving through the pump, heat builds up. Whether the cause is a loss of prime or a closed valve, the result is the same — a hot pump and hot, sometimes boiling, water. Usually, this hot water does not cause a problem when the pump is turned off and opened.

However, once in a while there is enough pressure left in the system to blow the hot water out of the pump and onto you. This scenario is most likely if there are valves in the system that prevent pressure from escaping, causing air pressure to remain in the filter, the solar collectors, or any other piping above the equipment level that can provide head pressure back to the system and cause a backflow when the pump is opened.

Your best defense is to turn the pump off and safely (keep your head clear!) open the filter air bleed before opening the pump. If no air escapes when you open the air bleed and there are no valves between the pump and filter, there should be no pressure in the pump either. In any case, placing a towel over the pump lid as you open it will help contain any blow-out should it occur. Treat this pump lid as you would your radiator cap and you’ll be on the right track.

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