It’s the first proper frost of the winter, the house is cold, and your boiler has stopped with a fault light flashing. Before you book a repair, check one simple thing. In freezing weather, the most common culprit is a frozen condensate pipe, and you can usually sort it yourself in a few minutes.
Our engineers at B & R Heating have been fixing boilers across Plymouth since 1982, and every cold snap brings the same calls. This guide explains what the pipe does, how to thaw it safely and how to stop it freezing again.
What Is a Condensate Pipe?
Every modern gas or oil boiler is a condensing boiler. It squeezes extra heat out of its exhaust gases, and as those gases cool they turn into water, a little like steam on a cold window. That water is mildly acidic, so it can’t just drip out of the flue. Instead it runs away through a plastic pipe, usually white or grey, about the width of your thumb.
Where to find yours
Follow the pipe from the underside of your boiler. On many homes it runs through the wall and down the outside to a drain or gully. That outside section is the part that freezes. If you’re not sure your boiler is a condensing model, our guide to condensing boilers explains how they work.
Why it freezes
The water in the pipe moves slowly, a trickle rather than a flow. When temperatures stay below zero for a few hours, that trickle freezes in the coldest spot, usually at a bend, a joint or the open end over the drain. The ice blocks the pipe, the water backs up into the boiler, and the boiler shuts itself down to protect itself.
Can’t find the pipe or worried about what you’re looking at? Call us on 01752 695050 and we’ll talk you through it.
Signs Your Condensate Pipe Has Frozen
A frozen condensate pipe nearly always shows itself in the same way. Look out for:
- A gurgling or bubbling noise coming from the boiler
- A fault code on the display, often after a cold night
- Heating and hot water both stopping at once
- The boiler restarting briefly, then locking out again
Common fault codes
On Worcester Bosch boilers, a frozen pipe usually shows as an EA or D5 code, or a slow flashing blue light on some models. Other makes use their own codes, so check your boiler manual or the manufacturer’s website. If the weather is mild and you see a fault code, the problem is probably something else, and it’s best to get an engineer to look at it.
Not sure what your code means? Read the code out to us on 01752 695050 and we’ll tell you whether it’s a quick fix.
How to Thaw a Frozen Condensate Pipe
This is a safe, simple job you can do yourself, as long as the frozen section is at ground level.
What you’ll need
A kettle, a jug or watering can, and a towel or old cloth. That’s it.
Step by step
- Boil the kettle, then let it cool for a few minutes until the water is warm rather than boiling. Boiling water can crack the plastic pipe or the joints.
- Find the frozen section. Feel along the outside pipe; the coldest spot, often the bend or the open end, is usually where the ice is.
- Pour the warm water slowly over that section. Repeat until you hear water running through the pipe again.
- You can also hold a hot water bottle or a warm cloth against the pipe for a few minutes.
- Once it’s clear, reset the boiler using the reset button. It should fire up and run normally.
When not to do it yourself
Never climb a ladder in icy weather to reach a high-level pipe, and never take the boiler casing off. If the pipe is out of reach, if the boiler still won’t restart, or if you can smell gas, stop. For a gas smell, leave the property and call the National Gas Emergency Service on 0800 111 999.
Thawed the pipe but the boiler still won’t fire? Call 01752 695050 and book one of our boiler repair engineers.
How to Stop It Freezing Again
Thawing a frozen condensate pipe gets you warm again tonight. A couple of small changes can stop it happening every winter.
Insulate the outside run
Waterproof pipe lagging from any DIY shop costs a few pounds and slips straight on. Cover every exposed inch, especially the bends. Worcester Bosch recommends insulating external pipework and fitting a cover over the open end at the drain.
Upsize or reroute the pipe
Older installations often used a narrow pipe outside, which freezes far more easily. Manufacturer guidance recommends a wider 32mm pipe for any outside run, kept as short as possible. Where it’s practical, an engineer can reroute the pipe inside the house to an internal waste, so it never meets the cold at all.
Keep the heating ticking over
During a hard frost, leave the heating on at a low setting overnight rather than switching it off. Worcester Bosch also suggests turning the boiler’s heating temperature control up to maximum during freezing spells, then back down once the weather warms up.
Plymouth winters catch people out
Plymouth’s coastal weather is milder than most of the country, so many outside pipes were fitted without lagging and only cause trouble in the odd hard frost. Homes further inland, around Ivybridge and the edge of Dartmoor, see colder nights and more frozen pipes. Your annual boiler service is a good time to ask your engineer to check the condensate pipe.
Want the problem fixed for good? Call 01752 695050 and we’ll quote to insulate, upsize or reroute your condensate pipe.
Frozen Condensate Pipe FAQs
Here are quick answers to the questions we hear most during a cold snap. If yours isn’t here, give the office a call and we’ll help.
Is a frozen condensate pipe dangerous?
No. It’s an inconvenience rather than a danger. The boiler shuts down on purpose to protect itself, and no gas escapes. Once the pipe thaws and you reset the boiler, it’s safe to use.
Can I use boiling water to thaw the pipe?
No. Boiling water can crack the plastic pipe or split the joints. Use warm water from a kettle that has cooled for a few minutes.
Why does my boiler keep freezing every winter?
Usually the outside pipe is too narrow, too long or not insulated. Upsizing it to 32mm, lagging it or rerouting it indoors normally solves the problem for good.
Will thawing the pipe damage my boiler?
No. Thawing the pipe and pressing reset is exactly what manufacturers advise. If the boiler won’t restart after two or three resets, stop and call an engineer.
Do you fix frozen condensate pipes in Plymouth?
Yes. Our Gas Safe engineers cover Plymouth and the surrounding areas, and can reroute, upsize or insulate your condensate pipe. If your boiler is old and keeps letting you down, we can also price a new boiler installation.
Boiler still not working after a freeze? Call B & R Heating on 01752 695050 or send us a message and we’ll get you warm again.
