Why is my boiler losing pressure? and other boiler FAQs

Helping ensure you have a reliable supply of gas to your home is one of our main priorities. However, when that gas enters your home there are several things that you’ll need in order to make use of it for hot water and central heating. A working boiler is essential in every home, especially during cold winter months. 
When your boiler loses pressure it can feel like a nightmare, so here are some things to check when you think your boiler might be losing pressure, or the pressure is too high.

Is your boiler pressure too high or too low?

Boiler pressure is the balance between air and water within your sealed boiler system. To increase energy efficiency, modern heating systems rely on the water with the pipes, radiators and boiler to be under pressure. This is because water pressure squeezes the bubbles within the water, meaning there is more water (a great conductor of heat) and not air (a poor conductor of heat) within the system.

If the pressure within the system is too low, or too high, this can cause problems and lead to inefficiencies that leaves the boiler running for longer. 

The boiler is equipped with safety devices that turn it off if the pressure isn’t right, often leading to “Fault codes” to be displayed. 

Most, if not all boilers, should have a pressure gauge on the front of them. This will help you quickly check if your boiler pressure is getting too high or low. The aim should be for boiler pressure to be somewhere between 1-1.5 bar. This is something that you can monitor yourself, please check the manufactures instructions for your boiler for more information. If you have to regularly “top up” the pressure, this could be a symptom of an underlying fault with the boiler. Contact a  Gas Safe Registered Engineer to investigate.

Has your boiler condensate pipe frozen?

When gas is burnt, as well as producing heat and light, it also produces carbon dioxide and water vapor – this is the steamy ‘plume’ that can be seen from a boiler flue on cold days. As this water vapor is ejected from the flue, water droplets form on the side of the flue and runs back into the boiler. Modern boilers are designed to catch this ‘condensate’ and drain it away through a ‘condensate pipe’. 
Condensate must be disposed of in the right way (into a suitable drain) because it contains contaminants that make it slightly acidic and would cause damage if left to drain onto surfaces or soil. 
All new boiler installations are condensate, so it’s likely you’ll have one of these if you live in a new home or a home where the boiler has been replaced in recent years. Your boiler condensate pipe can sometimes be found protruding from the walls of your property and leading into a drain and it’ll usually be made of plastic.


In cold weather, the water that passes through these pipes can become frozen, blocking the pipe and allowing condensate to build up in the boiler. To prevent itself from flooding, the boiler will switch itself off. It’s important to get this fixed as quickly as possible to avoid your boiler switching itself off and leaving your home without heat. 

Do you have a frozen boiler condensate drain?

So how do you know if you have a frozen boiler condensate drain connected to your boiler? One of the main signs of this problem will be that your boiler has turned itself off and left you without any heating or hot water. But before getting to that point, you may also notice a strange gurgling sound coming from your boiler and near the pipe outside your home.

Now would be a good time to try and locate your condensate pipe, helping you stay a step ahead if you do have any problems in the future. If you experience particularly cold and frosty weather, you can then carry out a quick check on the pipe to make sure everything seems to be in order – if you see water coming out, the pipe should be working.

If you do think you’ve diagnosed the problem of a frozen condensate drain, here are a few steps you could try to help clear the problem:

  • Apply a hot water bottle or a warm heated pad to the pipe in order to warm it up and begin thawing the water.
  • Fill a watering can or a jug with warm (not boiling) water and pour it over the pipe.

By doing this, you should start to notice the pipe clearing out any blocked water and functioning again. If you’re unsure whether you’ve cleared the blockage and are still experiencing problems with your boiler, contact a professional Gas Safe Registered engineer to take a look.

Any work directly on your boiler should always be carried out by a Gas Safe Registered engineer to ensure that it’s done safely and to a high standard. Ensuring your boiler is serviced annually will help to avoid these and many other problems, such as carbon monoxide leaks from your boiler.

If you are unsure of the cause of your gas appliance not working and think it may be a gas emergency, then call us on 0800 111 999* immediately.

*All calls to the National Gas Emergency Service and National Enquiry lines are recorded and may be monitored

My boiler is stuck on

I think we have no gas

Useful numbers

Some helpful numbers to call if you are experiencing issues with your gas appliances:

For a Gas Safe Registered engineer in your area call 0800 408 5500 or find an engineer.

If you have home care cover with your gas supplier please contact them directly.

For electricity issues or in the event of a power cut, dial 105.