The 12 most common boiler problems and how to fix them

Problems with your boiler or heating system can be a huge problem for your household, especially during periods of cold weather (which, let’s face it, can strike at any time of the year here in the UK)!

Being without hot water, heating or any other gas appliances, for that matter, can be a nightmare, so to help you troubleshoot and solve any boiler problems, we've put together this guide.

Here, we look at the 12 most common boiler problems and what you can do to investigate or solve them. We also explain whether you'll need a Gas Safe registered engineer to come and carry out any boiler repairs, so you can rest easy (and warmly) at night knowing that everything is running smoothly.

1. Leaking boiler

Depending on where it's coming from, a boiler leak may not be as serious as it first sounds. Sometimes a leak can be as trivial as a pipe fitting being in need of tightening. However, if you notice the leak is serious, you must call a Gas Safe registered engineer as soon as possible so the problem can be addressed before it becomes too severe to fix.

Noticing that your boiler system pressure has dropped, and needing to top it up, can be a sign that your boiler is leaking. You could also have a leak on the cold water supply into the boiler, or the hot water pipe going out.  When you notice this, go to the boiler and examine the pipes, looking to see if you can find any water dripping from a loose pipe fitting or damaged/corroded pipe. You should also have a look around your home for any patches of water beneath any radiators or pipework. Telltale signs of a leak somewhere in your home are stains on the carpet where dirty water has soaked in and dried and discolouration in the paintwork on your ceilings.

Although it may be nothing, a boiler leak can be serious, so you should call an engineer as soon as you notice it. You should never try to fix a boiler yourself.

Read more on leaky boilers - Is a leaky boiler an emergency?

2. Frozen condensate pipes

You need your boiler most in the colder months, so if it stops working in the depths of winter then it can be far more than just an inconvenience. One of the most common reasons why boilers experience faults in cold weather is a frozen condensate pipe.

As well as your heating not working, another sign that your boiler’s condensate pipe might be frozen is if it’s making unusual noises whilst firing up and trying to heat your home. Listen out for any gurgling sounds coming from your boiler or the pipes that carry hot water around your home.

Luckily, however, addressing a frozen condensate pipe is an easy fix. All you need to do is thaw it out, which you can do without having to phone an engineer.

To do this, get a jug of warm water and slowly pour it over the condensate pipe. Then, restart your boiler and wait to see if the problem has been fixed.

If you’re unsure about how to defrost your boiler’s condensate pipe, read our step-by-step guide, where you’ll find straightforward instructions.

3. Faulty pump and/or air in the system

Sometimes, one or more of the parts that make up your boiler can develop faults, leading to issues for your central heating system as a whole. This is especially common with older boilers, as the general wear and tear that comes as a natural consequence of years of constant usage takes its toll on things like the pump mechanism.

You’ll know if there is a problem with your boiler’s pump as it will display a fault code specific to its make and model, just the same as when there is any air trapped inside the system.

If your boiler pump is faulty, the signs to look out for are:

• Unusual noises coming from the boiler/clattering or even banging
• Water is leaking from the pump
• The pump casing feels hot to the touch
• No water coming from the boiler
• The pump will not switch off
• The boiler pump is not working at all
• Radiators take longer than normal to warm up or are not heating to the full temperature

4. Low pressure

As annoying as having low boiler pressure is, it can be surprisingly simple to fix. Most modern boilers use a filling loop, so all you'll have to do is pull it. Simply wait until the needle in the pressure gauge begins to move into the green section or until it reads anywhere between 1 and 1.5 bar.

Sometimes, however, low boiler pressure isn’t quite as straightforward to resolve. If your water pressure keeps dropping even after you’ve topped it up, you may have a leak somewhere within the system, or an issue within the boiler itself. At this point, the best thing to do is to contact a Gas Safe registered engineer who will be able to investigate the issue further and advise accordingly.

5. Your central heating works, but there's no hot water

Usually, if you have a system boiler installed and your heating is working, but strangely, you have no hot water. This could mean there’s an issue with your programmer, your hot water cylinder thermostat or even a faulty zone valve on your system. 

Faulty thermostat

If your hot water supply is working as it should, but your radiators or underfloor heating system is playing up, it could be a sign that there is a problem with your programmer room or smart thermostat. If you suspect that this might be the case, try restoring the thermostat to its baseline settings before attempting to readjust the temperature to your preferences.

This issue can be common with wireless thermostats if they are struggling to communicate with your boiler correctly. In this instance, try turning your home’s WiFi off and on again to see if that fixes the problem. Alternatively, if your thermostat is battery-powered, try replacing them with fresh ones to see if that does the trick.

If you are still not getting any heat into your radiators, you may have an issue with your heating zone valve or even your pump.

6. You have no central heating or hot water

Arguably the most annoying boiler problem is being left without both heating and hot water at the same time. This, quite understandably, tends to throw us into all sorts of stressful situations, so it’s important to get it sorted promptly. Having no central heating or hot water could be caused by several different problems, like a faulty pilot light, diverter valve or thermostat issues.

Low water pressure within the boiler and system could be the culprit, so the first thing to do would be to check your system’s pressure. It should be between 1.0 and 1.5 bar; if it’s not, then you’ll need to top it up by following the instructions detailed earlier in this guide.

7. Fault codes

Fault codes, sometimes referred to as error codes, are the strange mix of letters and numbers that appear on your boiler’s display screen when there’s some kind of fault at hand. They can signify a whole range of problems, from low boiler pressure to boiler lockout.

Depending on the particular fault code being displayed by your boiler, a quick reset or straightforward fix might be all that’s needed to get things sorted. Sometimes, though, the fault will be more serious and require an engineer to come and take a look.

To help you understand the fault codes with your boiler, explore our Ideal boiler fault codes blog, which explains what the various boiler breakdown codes mean and how to fix them. Don't own an Ideal boiler? Discover what the Worcester Bosch boiler fault codes mean here.

You can also head to the BOXT YouTube channel where you'll find a full range of helpful boiler error code videos. 

8. Cold radiators

If your radiators aren’t working properly (or, worse still, aren’t working at all), you’re going to want to get them fixed as soon as possible. There are a number of reasons why your home’s radiators might be experiencing issues but, fortunately, many of these can be fixed fairly readily without the need for an engineer.

The first thing to do is to have a feel around the radiator and check for any cold patches at the top of the radiator. If you do, try bleeding your radiator. Cold spots may mean that there is some trapped air in the system, so bleeding it should get things working properly again. If one or more of your radiators are heating up more slowly than others, then you might need to balance your whole central heating system.

Though this is a more labour-intensive process, it’s still something that you can do yourself by following the instructions in our how-to guide. Cold spots at the base of your radiators could also indicate that there is sludge/magnetite in your system which will require your  system to be power flushed.

9. Your radiators are making unusual noises

Boilers can make quite the racket when something isn’t working properly. Your radiators can be a clear indicator of when your heating system requires some maintenance too. If you hear some unusual boiler noise or your radiators are making a gurgling noise, this could be an indication that there is trapped air. If this happens, try to bleed the radiators to release the air.  

10. The boiler won't turn on

If your boiler isn't starting up, it may be because of an electrical issue. The first thing to do if your boiler won't turn on is check other appliances in your home to make sure the issue is isolated to your boiler.

Once you've tested other appliances and you know they're working, you can pinpoint it as a boiler problem as opposed to a wider electrical fault. Make sure the supply to your boiler is actually switched on and has not been turned off by accident

Your boiler not turning on could be caused by multiple issues within your boiler or central heating system. You should not attempt to investigate this issue further; instead, contact a qualified Gas Safe registered engineer to look into the problem and carry out any work.

11. The boiler is not heating water sufficiently

If you're finding that your boiler is delivering water and heating, but it just isn't hot enough, this can be a fault in one of the components on your boiler, like the thermostat, thermistor (a type of temperature sensor), a partially blocked heat exchanger or diverter valve. Don't attempt to carry out the repair yourself always contact a fully qualified Gas Safe registered engineer

12. The pilot light keeps going out

More commonly found on older boilers, the pilot light provides a small flame which lights the gas coming out of the main burner.

If the pilot light on your boiler keeps going out, it could be because of a faulty thermocouple switching off the gas supply or a draught getting to the boiler and blowing out the flame. This issue could also indicate that your boiler needs servicing. To solve pilot light-related issues, you should call on a Gas Safe registered engineer to inspect, diagnose and rectify the problem. It might just be that the appliance needs a service.

The importance of having your boiler serviced regularly

Booking an annual boiler service is crucial to ensuring the upkeep and maintenance of your boiler. Consistent servicing will help to identify any problems and ensure that boiler repairs can be carried out before any problems become too serious. A typical boiler inspection will review the following areas:

• The boiler's exterior, making sure the integrity of the case and seals are intact
• The internal parts, checking for damage, splits, cracks etc.
• The correct operation of the boiler flue
• The magnetic filter, cleaning to ensure it works correctly
• Gas pressure
• A check on safety devices within the boiler
• A combustion check to ensure the boiler is burning the gas correctly and safely

As well as identifying problems before they occur, having your system serviced annually will likely be expected of you as part of upholding the appliance's warranty - check your boiler manual for more information.

Having your boiler serviced will help to preserve and lengthen the life of your appliance too, meaning you won't have to fork out for a new boiler.

BOXT are here to help

If your boiler's driving you up the wall, don't worry - we're here to help. Get in touch with us via our live chat to speak to our experts. 

If you continue to have problems with your heating or hot water, it may be a sign that you need a new boiler. Simply include a few details about your property and current heating system and we'll recommend the most appropriate boilers for you with fixed price, no obligation quotes.