Winter Plumbing Checklist: Jobs to Do Before the First Frost

Why winter is when pipes and boilers fail

Winter plumbing trouble mostly comes from two places: water freezing somewhere it was never meant to get cold, and a boiler that sat idle all summer suddenly being asked to run flat out. You can see both coming, and most of the prevention costs little and fits into an afternoon.

Ice takes up roughly a tenth more space than the water it came from. In a sealed pipe that has nowhere to go, so copper bulges and splits along its length and plastic push-fit joints get forced apart. The damage happens during the freeze, but you only find out when it thaws and the water starts running into a ceiling. That delay is why a burst in a loft or under a floor can do so much harm before anyone notices.

The boiler side is different. Radiator valves and heating-side parts that have barely been used since spring can stick, pressure that crept down over the summer shows up as a lockout on the first cold night, and the plastic condensate pipe that drains a condensing boiler can freeze solid and shut the boiler down. Work through the list below in the order given: the water checks first, because they limit the worst damage.

The water checklist: stopcock, lagging and outside taps

Start with the stopcock, because every other emergency depends on it. Find it, turn it clockwise until it stops, open the kitchen cold tap to confirm the flow dies, then turn it back on. If it will not move by hand, do not force it with a wrench. A stiff old brass stopcock can shear its spindle, and then you have a leak you cannot stop. See what to do when a stopcock will not turn, or have a stopcock repair or replacement booked before the cold arrives.

• Stopcock: find it, close it, open it again, and make sure everyone in the house knows where it is
• Loft: lag every pipe and the cold water tank if you have one, but leave the area directly under the tank uninsulated so warmth from below can reach it
• Garage, utility room, cellar and under suspended timber floors: foam lagging on any exposed pipe, taped at the joints
• Outside tap: close its indoor isolating valve, open the tap to drain it, then leave it open; fit a tap cover if it has no isolator
• Kitchen cupboards on outside walls: note which ones hold pipes so you can leave the doors open on very cold nights
• Dripping taps and a running overflow: fix them now, because a slow trickle into an outside overflow freezes and blocks it

Foam lagging is sized by pipe diameter. Most domestic cold pipes are 15mm or 22mm; lagging a size too big leaves an air gap that does very little.

The heating checklist: pressure, radiators and the condensate pipe

Run the heating for an hour in October, well before you need it. A boiler that fails on a mild afternoon is an inconvenience; the same fault on a freezing night is an emergency with a queue for engineers behind it.

For a sealed system, the pressure gauge on the front of the boiler should read about 1 to 1.5 bar when the system is cold. If it has dropped below 1, top it up using the filling loop and note the date. If it keeps falling, you have a leak or a failing expansion vessel, and a boiler that loses pressure every day explains how to narrow it down.

Then bleed any radiator that is cold at the top, and recheck the pressure afterwards, because bleeding releases pressure. A radiator that stays cold at the bottom after bleeding usually has sludge in it, which is a service job rather than an emergency.

Last, go outside and look at the condensate pipe: the white or grey plastic pipe that leaves the wall near the boiler and runs to a drain. BS 6798, the standard gas boilers are installed to, recommends that condensate pipe running outside is insulated and at least 32mm across. A standard 21.5mm pipe running a long way down an outside wall is the classic frozen-condensate setup. Weatherproof lagging on the exposed run is a cheap job you can do yourself.

Nothing inside the boiler casing is a householder check. Gas work is carried out by Gas Safe registered engineers. If you smell gas, open windows, turn off at the meter if it is safe to reach, use no switches, and call the National Gas Emergency Service on 0800 111 999 from outside.

Settings to change on cold nights and when you are away

Turning the heating fully off to save money during a cold spell is the most common cause of a winter burst. Pipes in the loft and under floors are only protected by the warmth that leaks from the heated rooms.

• Set the thermostat so the house never drops below about 12°C, even overnight and when you are out
• Use the boiler or thermostat frost setting if it has one, and leave the boiler switched on at the fused spur
• On very cold nights, open the loft hatch and the doors of cupboards that hide pipes on outside walls
• If you are going away for more than a night or two, turn the stopcock off as well as leaving the heating low
• Keep radiator valves in rooms you do not use set to the frost symbol or 1, not fully closed

What to keep ready if something goes wrong

Keep a torch, old towels, a bucket and a set of water pump pliers somewhere you can reach in the dark. Label the stopcock with a tag so a visitor or a tenant can find it. Write down which switch on the consumer unit covers the boiler and immersion heater. If you rent, keep your landlord or agent’s out-of-hours number with the stopcock; our landlord emergency plumbing page covers who should be arranging what.

If a pipe does freeze, turn the stopcock off before you start to thaw it, open the tap it feeds, and warm it gently from the tap end back. How to thaw frozen pipes walks through it and lists what never to use. If a pipe has already split, the stopcock first, then the electrics near the leak, then what to do after a burst pipe.

When the checklist turns up a job for a plumber

Some things on this list are not DIY jobs, and it is far cheaper to have them done in October than at 2am in January. A stopcock that is seized or weeps at the spindle, a pressure gauge that falls below 1 bar within a week of topping up, a radiator valve that drips, an outside tap with no isolating valve, and pipe runs in a void you cannot reach to lag are all common finds.

A plumber fixing these while the weather is mild can usually do them in one visit, with the repair price agreed on site before the work starts. If you find a live problem, such as a leak or no heating on a cold night, that is when the £60 call-out at any hour makes sense; see how the pricing works.