condenser pipe

6 Vital Facts About Condensate Waste Pipes When Relocating Your Boiler

Are you about to relocate your boiler, but worried about the fact you need to run a condensate pipe?

If you’ve heard stories of condensate pipes freezing or being awkward to route to a drain – or even that it may have to run across the surface of a wall from the boiler to a drain – then you’re not alone.

As an experienced engineer, I find this fear and confusion is usually completely unnecessary. Fitting a condensate is actually quite straightforward, and there doesn’t have to be any drama. Even if your boiler is to be located quite far from a drain, there are actually plenty of options available. So, try not to panic!

Having fitted my fair share of condensates over the years, there are some things to know, however. Let me share the 6 most important facts about condensates with you below, so you can consider yourself clued-up.

1. All modern boilers can’t run without one

Essentially, a condensate pipe takes waste water away from the boiler. All modern condensing boilers require a condensate pipe to run to a suitable drain. There’s no way round it, so finding a suitable solution before installation is absolutely imperative.

However, there are plenty of options. It can be taken to the outside, run internally, or even pumped through a 10mm plastic tube rising vertically, then to a drain.

2. They can and will freeze when exposed to the elements

And the last thing you want is for that to happen in the depths of winter! So, if your condensate pipe is going to be external, ensure it’s larger than 22mm. It should be ideally 32mm (1 1/4″), lagged and have a good (fall) run down to the drain.

3. Laminate or concrete flooring can be tricky

It’s sometimes very difficult to get condensate pipes across concrete floors, or under the floor due to laminate flooring or tiles. If this is an issue, a pump can be used to collect the water and pump up and over to a drain. This can possibly be done through a void in a ceiling or a pipe box.

4. There can be underfloor problems, too

If a condensate pipe is running under a floor to connect to a drain, there are still potential issues. For instance, the pipe must be clipped or supported, so it will not sag with the weight of the water within. It must also have a good fall to the drain, otherwise water will lie in the pipe and be susceptible to freezing.

To avoid freezing, the pipe must also be lagged under the floor.

5. They contain slightly acidic waste water

Condensate waste water is slightly acidic, and care must be taken as to where it is drained. If, for example, you have an old property with a lead trap drain to an old sink, the condensate waste will burn through this within a few months.

It can be rerouted to another drain, or you can fit a PH equaliser which is a cartridge filled with limestone chippings that will fit on the pipe and neutralise the water as it passes through.

6. No drain? No worries with this solution

If the condensate discharges outside and no drain is available, a purpose made soakaway can be fitted. This must be fitted to the manufacturer’s specifications. In other words, the correct distance from the property, and the correct depth down, so dampness does not come into the house.

Again, this is filled with limestone chippings to neutralise the condensate water.

Advice from an experienced engineer

If your boiler is located quite far from a drain, it can be labour intensified. However, with modern solutions, the condensate water can be pumped through the pipe, meaning it doesn’t always have to run downhill. This was a problem in the past as if it didn’t run down (fall), the water stayed in the pipe.

If the only route is a long distance, and requires lifting carpets and flooring, it can up the cost and upheaval of your installation, and may take around 3 – 4 hours. But, it’s by no way an impossible task. As long as your engineer is experienced and fits to manufacturer’s instructions, there shouldn’t be an issue.

TIP: If you know you live on a snow line or an area very open to the elements, state this to your installer. There are now even heaters that can be fitted to stop your condensate freezing.

Just like many installers, when condensing boilers became popular we had condensate pipes freezing. It’s not good for clients, and it was costly for us having to go back to fix the issue. Having gained this knowledge, we always try to keep the condensate internal, or fit a pump. If the pipe has to go outside, we now take extra measures to ensure no issues in the future.

Finally, if a condensate pipe is taken to a rainwater pipe outside and is 32mm (1 1/4″), there must be an air break. This is so the water doesn’t back up and flood the boiler during heavy downpours or storms etc.


I hope this blog has been helpful when finding out all you need to know about condensate waste pipes. There are plenty of options, so you shouldn’t have to worry. However, speak to your chosen engineer, and see what they advise. It could be a relatively straightforward job. No dramas.

They might even be able to advise you on other options when relocating your combi boiler. You’ll never know if you don’t ask!

Finally, do you have any questions about condensate waste pipes when relocating your boiler? Let me know in the comments. I’m here to help!

Worried about fitting a condensate waste pipe when relocating your boiler? This blog is here to tell you why you shouldn't be.

How to fix a frozen boiler condensate pipe

There are few things more enjoyable than breakfast with the family on a cold, frosty morning. Seeing the clear blue sky, bright sunlight and beautiful white frost outside while you are nice and warm indoors makes such mornings worth all the effort – unless you wake up freezing to discover that your combi boiler has unexpectedly stopped working.

If you have found that your gas boiler is suddenly not working when the weather goes cold, it is highly possible that you have a frozen boiler condensate pipe.

Read on or watch the video to learn more about how to diagnose, solve and prevent this very common problem.

Understanding your boiler condensate pipe

What is a condensate pipe?

SInce 2005, it has been a UK requirement that all gas combination boilers use condensing technology to increase their efficiency.

Condensing technology allows heat existing in the flue gasses to be captured and ‘recycled’ back into the heating system to heat the water inside the boiler. During the condensing process, the temperature of the flue gas is reduced from around 130℃ to 50℃.

This rapid fall in temperature causes condensation, which needs to be drained – as much as 2 litres per hour for an efficient boiler.

The boiler condensate pipe is the pipe that allows this water to be drained from the heating system and disposed of with your household waste water. Although it is advised that this pipe is connected to your waste water system internally, there are many situations where this is not possible and instead the pipe will be fitted externally, leaving it vulnerable to becoming frozen in extremely low temperatures or prolonged cold spells.

Condensate pipes that run through wall cavities or unheated outbuildings such as garages are also at a higher risk of freezing.

How to find your boiler condensate pipe

Because metal piping cannot be used, the condensate pipe is relatively easy to identify. It will be the only plastic pipe connected to your boiler.

Due to UK legislation the pipe will typically be 22mm in diameter if the drainage system is connected internally, and may be 32mm where the pipe is drained externally. The increased size helps to prevent internal freezing, but will not completely eliminate the risk.

Outside, the condensate pipe should be a relatively short length of pipe that connects directly to your drainage system, and should also be steeply angled to ensure that other waste water, for example from appliance outflows, is not able to travel up it.

It will often emerge at around the same height as your window sills. Ideally, it will be well clad but this may not always be the case, especially in a country like the UK where we are not used to extreme cold.

Fixing and preventing a frozen condensate pipe

How do I know if my boiler condensate pipe is frozen?

The first indication that your boiler condensate pipe is frozen will usually be that you have no hot water and heating, even when you are sure your boiler has been working absolutely fine. You may also be able to hear an unfamiliar gurgling sound coming from your boiler.

On closer inspection of the boiler control panel, you will find that the boiler has stopped operating. If the condensate pipe has become frozen, the boiler’s sensors will detect that it has become blocked and prevent the boiler from operating. This is a normal safety precaution to prevent damage to the boiler.

Depending on the make and model of your boiler, different fault codes may be displayed. If you have a Viessmann Vitodens gas boiler it is likely you will see an ‘F4’ error on the display, full details can be found in our fault code tool.

For safety, you will not be able to reset and relight your boiler until the obstruction in the pipe has been cleared.

In many cases, it is the exit that has frozen, often due to the water trickling out gradually turning into a build up of ice or becoming immersed in frozen water. This can be easily confirmed with a visual inspection.

A frozen boiler condensate pipe is a surprisingly common problem for gas combi boilers in winter. Here’s how to find, fix and prevent the problem.