Thaw a frozen boiler condensate pipe

Thaw your boiler's frozen condensate pipe safely with warm water, then insulate it to stop it freezing again.

CP-01Check for a frozen condensate faultLook at the boiler display for a fault code such as EA229, F.4 or similar — most makes show a specific lockout code for a blocked or frozen condensate pipe. This usually happens overnight when outside temperatures drop below 0°C. Go outside and find the white plastic pipe running from the boiler through an outside wall down to a drain or gulley.

CP-02Switch the boiler offTurn the boiler off at its own switch, or isolate it at the fused spur or socket. This lets it sit safely while you work on the pipe outside and stops it trying to fire while blocked. Do not try the reset button yet.

CP-03Get warm water ready, not boilingFill a jug or small watering can with warm water from the tap, no hotter than you'd use for washing up. Never pour boiling water on the pipe — sudden heat can crack the plastic. Put on rubber gloves and take care outside if the ground is icy.

1 pair · Rubber gloves

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CP-04Find the frozen section of pipeFollow the pipe from where it leaves the wall down to the drain. Freezing usually happens at the lowest exposed point, often a U-bend near ground level, or wherever the pipe is thinnest and most exposed to wind. Check for ice sitting visibly in the clear end of the pipe.

CP-05Pour warm water over the frozen sectionWorking from the highest point down, pour the warm water slowly over the pipe. For a stubborn blockage, wrap a cloth soaked in warm water, or a hot water bottle, around the pipe and hold it there for a few minutes. Repeat as needed until the ice clears.

1 each · Hot water bottle

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CP-06Reset the boiler and test itOnce you're confident the ice has cleared, press and hold the reset button for around 3-5 seconds. Turn on a hot tap to trigger the boiler and listen for water gurgling away through the condensate pipe. If it fires up and stays on, the blockage has cleared.

CP-07Insulate the pipe to stop it happening againWrap the exposed outside section of pipe with foam pipe lagging, at least 13mm wall thickness, securing it every 150mm with clips or tape. If the pipe keeps freezing despite lagging, it may need rerouting to run internally or through a bigger-bore pipe — this is work on the boiler's own pipework and should be done by a Gas Safe registered engineer, not DIY.

RULES

1 each · Pipe lagging (2m length, 13mm wall)

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KNOW THE RULES

Altering pipework connected to a gas boiler falls under the Gas Safety (Installation and Use) Regulations. Only a Gas Safe registered engineer can carry out this work.

CP-08Tidy upMop up any puddles left from the thawing process near the boiler or drain. Wring out and dry any cloths used, and put the hot water bottle away. Keep an eye on the pipe during future cold spells.

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