Winter drainage: preventing frozen, cracked and surcharging drains

Cold weather does not usually freeze a healthy, free-flowing drain. It freezes the ones that were already running slowly. That is the single most useful thing to understand about winter drainage — freeze problems are almost always blockage problems that showed up in January.

Why drains freeze

Moving water carries heat and resists freezing. A drain that flows properly empties between uses and rarely holds enough standing water to freeze. A drain with a partial blockage holds water in the pipe, and shallow or exposed sections — external gullies, condensate pipes, shallow runs under paths — freeze solid from that standing water.

Before the cold arrives

1. 1Clear any slow-running drain now — do not wait to see if it copes.
2. 2Lag exposed external pipework, especially boiler condensate pipes and small-bore waste runs.
3. 3Degrease kitchen and catering waste lines; cold weather hardens fat deposits and turns a manageable film into a full blockage.
4. 4Check manhole and chamber covers seat properly so surface water and grit are not washing straight in.
5. 5Test pump station alarms and float switches while conditions are still mild.

If a drain or condensate pipe freezes

• Apply warmth gently — a cloth soaked in hot (not boiling) water wrapped around the pipe, or a hot water bottle.
• Never use a naked flame, blowtorch or boiling water on plastic pipework; you will crack it.
• Work from the open end back towards the blockage so meltwater can escape.
• Once flowing, get the underlying blockage cleared — the freeze will simply recur.

Storms and surcharging

Winter storms push combined and surface water systems to capacity. Surcharging — where water backs up out of a manhole or gully — is a sign the system downstream cannot take the flow. Sometimes that is the public sewer under load; often it is a partially blocked private run that has no spare capacity left. Anti-flood devices and non-return valves are worth considering on low-lying properties with a history of backing up.

Pump stations in winter

Pump stations work hardest in winter, when rainfall ingress increases run cycles. A pump that was borderline in September will fail in January. Check the alarm sounds, the floats move freely, and the wet well has been emptied and cleaned within the last twelve months.