Cold-Weather & Freeze Protection for a ZWL Pump

Here’s a detail that catches people out in cold climates: a self-priming pump keeps a charge of liquid *inside* the pump body between runs — that’s how it re-primes. In freezing weather, that stored liquid can freeze, and a block of ice can crack the casing or stop the pump from starting. A little winter care keeps a ZWL direct-coupled self-priming sewage pump reliable through the cold.

The freeze risk, and the simple fix

The pump has a drain plug (bottom drain) at the base for exactly this reason. If the pump will sit idle in sub-zero conditions, drain the pump body through that plug so there’s no liquid left to freeze. Before the next start, refill it (at least two-thirds of the body) through the filling valve, and it primes as normal.

For a pump that must stay ready to run in winter, alternatives to draining are:

• keep it running or cycling so the liquid doesn’t sit still and freeze,
• trace-heat and lag the pump body and exposed suction pipe, or
• house it (though the ZWL’s outdoor-motor option is often used precisely to avoid a building — so trace heating is the usual answer).

Also mind the suction line and medium

A frozen suction line won’t prime either — insulate or heat-trace exposed pipe. And remember the medium itself: if what you’re pumping can freeze or turn to slush in the pit, that’s a process issue to manage separately.

Cold-weather notes

• Idle in frost → drain the pump body via the bottom drain plug; refill before restart
• Must stay ready → cycle it, or trace-heat and lag the body and suction pipe
• Refill: at least two-thirds of pump body before starting
• Insulate exposed suction pipe against freezing
• Material: cast iron or stainless steel