Unusually cold weather in the UK is starting to play havoc with boilers, with many of us waking up to no heating or hot water. If this is you, you may find that your boiler is flashing up an error message on its screen, or making strange gurgling noises.
As annoying as this is, with temperatures below freezing, the likely culprit for your problems with modern condensing boilers is a frozen condensate pipe.
Condensing boilers produce slightly acidic condensation as a byproduct, which is expelled via a pipe to the outside of your house via a polymer pipe. When the temperature drops, this pipe can freeze, eventually creating a blockage and preventing your boiler from working.
Although boilers are supposed to show an error message that helps you track this down, sometimes it’s not that simple. For example. my Glow-worm boiler has shown error messages F1, F9 and F13, even though the problem is the same.
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Before you start, turn your boiler off at its dedicated switch. If your boiler is on the ground floor, go outside and look for a plastic pipe that comes out from the wall that your boiler is mounted on. If you can see the end of it, take a look and see if it’s frozen throughout; if you can’t see the end, then it’s worth trying the method to fix it anyway. If you can’t see a pipe coming through the wall, you may have an older type of boiler and will need to call a heating engineer.
Likewise, if your boiler is mounted higher up, it’s dangerous to get to, so you’ll need to call a registered heating engineer.
Now, you need to thaw out the pipe, clearing the ice blockage. You can strap a hot water bottle to the pipe, although this takes time. The better option is to use warm water to melt the ice. Don’t use boiling water, as this could be dangerous; start your a kettle, but cut it off when the water is warm, but not boiling.
Now, go outside and pour the warm water up and down the length of the condensate pipe. Use a full kettle-load of water to make sure that you’ve got everything out; at my house, a popsicle-like block of ice slid out of the pipe. Repeat this step as necessary.
Now, go back in and turn your boiler on. It should start automatically, running through a startup cycle. If you still get an error message (I did on my Glow-worm), then you may have to reset the boiler by checking the manual (these are available online if you Google the manufacturer and model name). My Glow-worm has a reset button that you can push with a pin, underneath the display.
With the boiler fired up, you can now try your heating or, if you have a combi-boiler, turn on the hot water. The boiler should fire into life, and you should get hot water.
However, I had to go through an extra step, as my boiler had also lost a bit of pressure and wouldn’t start. Boilers should be pressurised to 1bar. To top up, you need to open the filling loop, turning off when the boiler’s display indicates 1bar (a little over won’t cause any harm, say 1.2bar). On my boiler, the filling loop consists of two taps located underneath the boiler; both must be opened to fill and both closed when done. Your boiler’s manual will tell you the correct procedure if you’re not sure.
If your boiler is at the correct pressure and not working, do not fill it further, as this could damage it. If you’re not confident doing this step, then it’s best to call a heating engineer. Given that you had a problem with your boiler, it’s a good time to book a service and get it looked at properly, anyway.
How to prevent the condensate pipe freezing
To prevent further issues, you can try lagging the pipe, insulating it from cold weather. A lot of boiler installations use small pipework for the condensate pipe, but larger pipes (25mm+ in diameter) make it harder for the ice to block the run. When you get your boiler serviced, you can ask the engineer to make these changes for you.
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