Boiler Condensate Pipe, What is it and What Does it do?

James Elston
Written by James Elston
Updated on 1st December 2023
Posted on 30th November 2023
Topic: Boiler Advice
boiler condensate pipe

When the UK experienced sub-zero temperatures in 2010 and 2018, boiler manufacturers received thousands of calls from people with condensing boilers.

The problem: the boiler condensate pipes froze and caused the boilers to shut down, however, most problems occurred because the pipe was located outside the house.

As much as it makes no difference to the untrained eye, it is still important to understand the mechanisms of a condensate pipe to prevent problems in the future.

Get an online fixed price in 20 seconds:

What kind of fuel does your boiler use?

What is a boiler condensate pipe?

A condensing boiler won’t work without a boiler condensate pipe. The pipe is responsible for discharging wastewater from the boiler into the sewer.

Every time a condensing boiler works, it produces a condensate. Condensate is water produced from the process of condensation.

Modern gas boilers can recycle latent heat from waste exhaust gases. The condensate comes from carbon dioxide and water vapour by-products.

As soon as the needed heat is produced from the vapour, it condenses back into water form. The liquid is then collected for its thermal energy. The remaining product is washed out through the condensate pipe.

The wastewater is somewhat acidic. So, the wastewater must travel through a plastic pipe.

The boiler condensate pipe is mostly made from PVC pipes popping out of the external wall.

How to identify a boiler condensate pipe

Distinguishing which one among the attachments is the boiler condensate pipe makes the repair easier. As mentioned, a boiler condensate pipe is made from plastic. So, look for a plastic pipe among the metal ones.

HHIC condensate pipe guidelines to know for new boiler installation

water drops on a metal pipe

The Heating & Hotwater Industry Council is an organisation that supports and promotes the sustainable domestic heating and hot water industry in the United Kingdom.

The UK legislation also provides specific diameters for manufacturers to follow for combi boiler installation in the UK.

For the drainage system connected internally, the diameter of the pipe must be around 22mm. For an external pipe, however, it should be around 32mm.

The 10mm size difference somewhat prevents freezing. But, condensate pipe freezing cannot be eliminated despite the increase in diameter size. An external condensate pipe must also have a shorter length connecting straight to the drainage system.

Outside pipes meant for sink wastes and washing machines must be insulated with waterproof and UV-resistant materials.

Most frozen pipes occur at the exit when the water comes out freezes or starts building up ice. To prevent this problem, cut the end of a waste pipe at a 45-degree angle. The end should be pointed to the grid in a gradual fall to minimise pipe freezing.

Fixing a broken condensate pipe

Boiler condensate pipe regulations may prefer you get a professional Gas Safe engineer. The heating engineer knows how to assess the pipework, fittings, and other issues related to the damage.

If the problem is simply freezing, you may fix it on your own. These are a few hacks that can help you deal with a frozen condensate pipe.

If it is broken, however you will need to replace your condensate pipe to stop leaks and other further problems arising.

Signs of a frozen condensate pipe

The main problem with a boiler condensate pipe is freezing. The pipe usually freezes during cold weather. Condensate pipe freezing is a huge problem during the winter months. When this happens, you’ll find yourself without proper heating at home.

A frozen condensate pipe will show the following signs:

  • No heating and hot water
  • Boiler shows an error code/message
  • Strange gurgling sounds

While you cannot control how cold the temperature can be, you can do something to avoid freezing pipes.

  1. Insulate the pipe. Pipe insulation is a do-it-yourself process. Use waterproof lagging when insulating. This is important since non-waterproof materials may do more harm than good.
  2. Move the condensate pipe inside. Transferring the condensate pipe internally guarantees that it won’t fall below room temperature, and this will prevent freezing. However, this should be done by a heating engineer or installer.
  3. Increase the temperature – You could increase the boiler flow temperature but this could cost you more in energy bills in.

Read more about what to do if you have a boiler not working here

Can a condensate pipe help save more money?

Condensing boilers work by recovering more heat as they recycle gases. It is a better choice than non-condensing boilers when saving money from expensive energy bills. And since a boiler condensate pipe is a part of a condensing boiler, it does help you save money.

Increasing the efficiency of your boiler by getting one with condensing technology means it will be much cheaper to run your central heating system all year round.

What are condensate pumps?

condensate pump

A type of centrifugal pump, a condensate pump collects and disperses hot water and other liquid generated by the condensation process of the heating system.

A pump is used when gravity cannot naturally move the water and expel it to the drainage at ground level.

The condensate pump does not work continuously but rather intermittently.

A collection tank collects the condensate. A float switch activates the pump once the accumulated liquid reaches a certain level. The condensate is expelled from the tank, making enough room for a new cycle of condensate collection.

There are also condensate pumps with two switches, which is a good blockage indicator. When the condensate reaches the first switch, the pump should activate and expel the liquid from the tank.

But if the pipe is frozen, the pump won’t be able to move the liquid out the pump. The condensate level will continue to rise and hit off the second switch, which will shut off the system or make an alarm sound.

No drain? soakaway

The solution is a soakaway when there is no drain for the wastewater to exit from.

What is a soakaway, and how does it work?

A soakaway catches the water waste and neutralises its acidic nature through the help of limescale chippings. It controls the release of condensate water so it can get into the ground safely.

Benefits of a soakaway

A soakaway reduces the pressure on the burdened main drainage system since the water has some other place to go. It is also very easy and affordable to install.

Soakaways are low-maintenance and can even provide a rebate against surface drainage costs if your sewer company offers them.

Another benefit of using a soakaway is reducing acidic residue within the system. Thereby extending the boiler’s lifespan and ensuring that the central heating system works well throughout.

Disadvantages of a soakaway

While a soakaway is a good alternative, some issues may arise if you don’t have a drain for your boiler condensate pipe. First and foremost, a soakaway shouldn’t be used in soil with poor drainage as it will do more harm than good.

Secondly, dirt and leaves may block the soakaway causing it to get clogged. To prevent this, install a silt filter to screen leaves and dirt from coming inside.

The soakaway should also be installed far away from the house so that it won’t affect the structural foundation if drainage problems occur.


How much condensate water waste does a condensing boiler produce?

Typically, a modern condensing boiler can rack up two to three litres of water waste for every hour of boiler operation. The water isn’t released in full but in increments of 300 mL to reduce the risk of freezing the external pipe.

What is the ideal water temperature to melt the frozen water in the pipe?

A temperature of 60⁰C to 70⁰C is ideal for melting the freezing pipe. However, pouring warm water on the frozen section may not work the first time. You have to do it repeatedly for it to work, depending on how bad the blockage is.

Does pouring warm water work all the time?

Even if you pour warm water on a frozen condensate pipe several times, it might not work if the temperature is -2⁰C or below. At this temperature, the hot water you pour can freeze quickly and make matters worse.

A remedy for this problem is to combine the water pouring method with a hot water bottle.

Pour the warm water first, then apply a hot water bottle for as long as needed. This technique has a better chance of melting the blockage.

Written by
James Elston
James Elston Director Of Boiler Central
Posted on: 30th November 2023
Topic: Boiler Advice

James Elston is our resident boiler replacement and heating expert here at Boiler Central. With over 20 years experience in the boiler installation industry, James ensures that he knows everything there is about our Gas Safe boiler installations, energy saving and home heating solutions. This can be from simply procuring the latest best combi boilers, to reviewing and ensuring that Boiler Central maintains the highest standards across our boiler installation company.

Buy a new boiler in minutes

Instant online quotes. Nationwide next-day fitting

Get my fixed price
Get a great price on a Which? Best Buy boiler online in 20 seconds
  • Over 15,000 boiler installed
  • Rated Excellent on Trustpilot
  • Fair, fixed and final prices
  • No pushy salespeople
  • Next-day installation
  • 0% deposit interest-free finance
Next-day fitting available until 2pmGet a quote now >