If you’ve had a new gas boiler installed in the last 15 years, it will most likely be a high-efficiency condensing boiler. In simple terms, a condensing boiler can extract heat from the water vapour in exhaust gasses by passing the gasses through something called a condenser. The condensed water vapour (now just water) then leaves the boiler through something called a condensate pipe.

The condensate pipe is usually a white PVC-U pipe, similar to one you may find on a washing machine or sink waste pipe which usually goes outside into a drain. It’s worth noting that boiler condensate can be slightly corrosive to certain materials, especially metals. That’s why condensate pipes are usually made of plastic and not metal.

Is it important?

Once the water vapour has been condensed, it turns into water. A condensing boiler, on average, creates around 2 litres of condensate water per hour, and it needs somewhere to go! By having a condensate pipe, the water is safely disposed of with the rest of the waste water, just like a sink or washing machine.

Where to find it

You’ll usually find your condensate pipe leaving your home at the nearest outside wall. It usually looks like a small, white pipe starting from the wall, then heading down into a drain or run off system. Condensate pipes can sometimes be connected straight into wastewater flows, such as the waste pipe of a sink.

Impact of a frozen condensate pipe

During low temperatures it’s possible for your condensate pipe to freeze if the pipe terminates outside of your property as water is passing through the pipe. If this happens, it is most likely that your boiler will fail to start, meaning no heating or hot water.

If a frozen condensate pipe is to blame for your boiler failing to start, it means that you have to defrost the water that has built up within the pipe before it will work again.

How do I know if my condensate pipe is frozen?

Before attempting to thaw a frozen condensate pipe, it’s important to make sure that’s the cause of the problem. The first warning sign that your condensate pipe has frozen may be an error code on your boiler. Another tell-tale sign is a gurgling noise coming from the boiler. If the boiler was working fine up until a bit of a cold snap, there’s a strong chance your issue is a frozen condensate pipe.


Find out more about how to defrost a frozen condensate pipe on your boiler and how to protect it by checking out Vaillant’s handy tips here: https://www.vaillant.co.uk/homeowners/advice-and-knowledge/heating-tips/top-tips-to-keep-your-home-warm-this-winter/condensate-pipe-1561987.html


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