Frozen outdoor pipes — how to thaw and prevent
⚠️ Never use a gas torch or heat gun on plastic pipes or on any pipe within a wall. Do not use boiling water — the sudden thermal shock can crack copper or plastic fittings.
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Most likely cause & what to check
External pipes — outdoor taps, garden supply pipes, pipes in unheated outbuildings — are the first to freeze when temperatures drop below zero. Signs of a frozen pipe: no flow from the outdoor tap, no flow in the shed or garage, or an unusual hissing when the internal stopcock is opened.
Turn off the indoor isolating valve for the affected pipe. This isolates the frozen section and prevents a burst pipe from flooding when it thaws.
To thaw, work from the tap or outlet end back towards the house — this allows the ice to melt with an exit route. Apply a hair dryer on low heat, a warm water bottle, or pour warm (not boiling) water over lagged cloths wrapped around the pipe.
Once flow is restored, open the tap fully for 30 seconds to flush any debris. Check all compression joints and push-fit fittings for leaks — freezing can crack fittings or break the olive seal inside compression joints.
Insulate the pipe immediately once thawed. Use closed-cell foam pipe lagging (£2–£4 per metre) with self-adhesive tape at all joins. For outdoor taps, a proprietary outdoor tap cover (£5–£10) adds significant frost protection.
For the future: in October, close the indoor isolating valve to the outdoor tap and open the outside tap to drain the exposed section. Leave the outside tap open slightly over winter so residual water can drain. A garden tap with a built-in drainage cap makes this simple.
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Frequently asked questions
At what temperature do outdoor pipes freeze?
Water pipes begin to freeze when the temperature drops below 0°C for a sustained period. Exposed outdoor taps and pipes in unheated outbuildings can freeze within hours during a hard frost. Pipes in lofts and under suspended floors are also at risk if insulation is inadequate.
How do I lag outdoor pipes to prevent freezing?
Use closed-cell foam pipe lagging, available from any hardware store in standard sizes (15mm, 22mm diameter). Secure at all joins with waterproof tape. For an outdoor tap, a proprietary insulated tap cover (£5–£10) over the whole tap fitting gives good frost protection. Drain the pipe section in October as an added precaution.
Can I use a heat cable on outdoor pipes?
Yes — self-regulating heating cables (frost protection cables) can be wrapped around exposed pipe runs and plugged in. They only draw power when the temperature drops near freezing, making them economical to run. They are particularly useful for long exposed pipe runs that cannot be easily lagged or drained.