There is a specific January call we get more than any other, and the person making it is always confused, because on the face of it nothing is broken.
The pump is running. The breaker has not tripped. The pit is full anyway, and the floor is getting wet.
The pump is almost never the problem. The problem is that the water has nowhere to go.
How the failure works
A sump pump discharges through a pipe that leaves the house and dumps the water somewhere outside. In a Simcoe County winter that exterior pipe is sitting in air that stays below freezing for weeks. Barrie sits in the snow-belt off Georgian Bay, so the run is usually buried in snow as well, and a pipe under a drift gets no help from the afternoon sun.
Any water left in it after a pump cycle can freeze. Once a plug forms, the next cycle pushes against it, backs up, and drains straight back into the pit through the check valve. The pump sees a full pit, runs again, and does it all over.
What you get is a pump that never stops, water that never leaves, and eventually either a burned-out motor or a tripped overload — with a basement filling up the whole time.
The cruel part of the timing: this happens during a January thaw, which is exactly when the pit is getting the most water.
Why it is worse than it sounds
Two things make this failure nastier than a straightforward pump failure.
It is silent in the way that matters. A dead pump is obvious — no noise. A pump fighting an ice plug is making all the right sounds. People hear it running and assume it is coping.
Battery backup does not help. Backup pumps are sold, correctly, as insurance against power failure. They do nothing at all here — the backup pushes at the same frozen pipe. If you have spent money on a backup and think you are covered for winter, you are covered for one of the two winter failure modes.
What actually prevents it
Give the water an alternative exit. The single most effective measure is a relief point on the discharge line close to the house, so that if the main run freezes the pump can still push water out somewhere. Vented adaptors that do this are a standard fitting and they cost very little.
Keep the exterior run short and steep. Long, flat runs hold water. A short run with real pitch drains itself after every cycle, and a pipe with no standing water in it cannot form a plug. The long, flat run is the common shape on the wider lots in Springwater and Oro-Medonte, where the pipe is often taken well away from the house before it is allowed to discharge.
Get the outlet away from the foundation, and away from where snow gets piled. A discharge that dumps two feet from the wall is feeding your own backfill trench — which is the problem you installed the pump to solve. An outlet buried under a plough bank freezes first.
Check the check valve. A failed check valve lets the column of water in the vertical run fall back into the pit after each cycle. That is exactly the standing water that freezes.
If it is happening right now
Do not keep letting the pump cycle against the blockage — you will lose the pump on top of everything else. Unplug it, get the water out however you can, and find the frozen section. Frequently it is the last exposed metre before the outlet, and it is reachable.
Then fix the exit before next winter, rather than buying a bigger pump. The pump was never the weak point.