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Construction and Repair
27 October 2021

Top 10 Most Common Boiler Problems

Boiler Problems

Your boiler not working is an inconvenience at the best of times.

Fortunately, many boiler problems are common and can be repaired by a professional heating engineer or, in some cases, can even be sorted yourself.

To make recognising a fault as straightforward as possible, modern boilers display a digital boiler error code to let you know exactly what's causing the fault.

These are the top 10 most common boiler problems:

Common boiler problems:


1.       Hot water but no heating

2.       No heat or hot water

3.       Boiler is leaking

4.       Boiler is kettling

5.       Noisy boiler (e.g. banging, whistling, gurgling)

6.       Low boiler pressure

7.       Frozen condensate pipe

8.       Radiators are cold

9.       Boiler keeps switching itself off

10.   Boiler isn’t responding to the thermostat


1. Hot water but no heating

A boiler should provide your home with central heating and domestic hot water. If you've found that you're getting hot water from the taps but no central heating, there's a problem.

When you have no central heating, first make sure your thermostat is working then check to see if the boiler pressure is too low.

Thermostats allow you to control the temperature of the central heating, as well as the time it should come on. If the heating hasn't come on at the expected time, double check the settings.

Boiler pressure is a term used to describe the pressure of the hot water running through the central heating system. Should the boiler pressure drop too low, the central heating will fail to work.

Increasing the boiler pressure is something you can do without calling out a heating engineer (take a look at our simple guide here). However, if you're the slightest bit unsure, don't hesitate to contact a professional.

Thermostat troubles and low boiler pressure aren't the only reasons why you might have domestic hot water but no heating. Unfortunately though, this is where it gets a little more complex…

If your thermostat is fine and the boiler pressure is high enough, there could be a fault in need of professional repair. Common causes of hot water but no heating include broken diaphragms and airlocks or a failure of the motorised valves.

For heating systems that include a combi boiler, there could be an issue with the diverter valve. Combi boilers provide heating and hot water on demand and the diverter valve directs the hot water to either the radiators or the hot water outlets. In the event that it gets stuck, you could end up with hot water but no heating, or vice versa.

A Gas Safe registered engineer will be able to diagnose faulty diaphragms and airlocks, motorised valves or diverter valves and carry out the necessary repairs or replace broken parts.


2. No heat or hot water

You should be able to rely on your boiler to provide your home with heating and hot water. If you find that it isn't able to do either then you'll want to get it fixed as quickly as possible.

There's no single issue that can lead to your boiler failing to provide heat or hot water.

Before jumping to conclusions about potential faults, check that power is being supplied to the boiler.

If your boiler is receiving power then we can begin looking further into possible issues. Your boiler should display an error code to help you locate the source of the problem.

However, to give you some ideas, possible issues include:

Fuel isn't making its way into your property. If you have a gas boiler, ensure that your gas supplier is still supplying fuel. Should you have an oil boiler make sure there's plenty of fuel in the storage tank.

Double check the thermostat settings and set the desired temperature higher than the current room temperature

The condensate pipe has frozen and needs thawing out (we'll come onto this later in the article)

Low boiler pressure so ensure the boiler pressure is set according to the manufacturers instructions (usually between 1 and 2 on the pressure gauge)

Older boilers will have a pilot light (a small flame that constantly burns before lighting a larger flame when heating or hot water is needed). If the pilot light goes out then the boiler won't be able to fire into action.


3. Boiler is leaking

A leak coming from your boiler is never a good sign. And the cause of the leak will depend where the water is coming from.

Before attempting to locate the cause of the leak, stop the water supply and turn off the central heating.

It's important to note that you should never attempt to repair a boiler leak yourself – always call out a Gas Safe registered engineer.

The most common cause of a leaking boiler is a broken internal component, such as a pump seal or pressure valve. If the leak is coming from the pressure valve it could be the case that the boiler pressure is too high. Meanwhile, a leak from the pump seal is a sign that it may have worn out and need replacing.

In the case that the boiler is leaking around the pipes or tank then that's a strong indication of corrosion. Otherwise, it could be the result of a poor installation. Either way, we recommend calling out an engineer who will be able to diagnose and fix the leak.


4. Boiler is kettling

Hearing a strange rumbling noise similar to when a kettle is boiling? When lime scale or sludge builds up on your boiler's heat exchanger (a coil that transfers heat from the fuel to the water that will circulate around the heating system) you can get something called kettling.

When debris builds up in your boiler, it can restrict the flow of water within the heat exchanger. This can overheat the water, causing it to steam and boil – causing kettle-like sounds.

Kettling is more common in areas with hard water, but can affect boilers in soft water areas too. Not only does it cause your boiler to work harder and thus cost more to run, it can also shorten the system's life.

If your boiler is kettling, it's advisable to call out a Gas Safe registered engineer. The engineer will likely flush out your system to remove the build-up of these deposits and ensure the system is working properly once more.


5. Noisy boiler (e.g. banging, whistling, gurgling)

From banging and clanging to whistles and gurgles, a heating system can make a number of noises caused for a number of reasons.

If you hear a noise coming from the boiler or heating system, don't ignore it as there's probably a fault.

The potential fault will vary depending on the type of sound and where it's coming from. We've listed some common boiler noises below to help you find the cause.


We've already covered kettle-like sounds, caused by a build-up of sludge on the heat exchanger.


Banging will commonly be caused by the pipework or an internal component coming loose but could also be the result of debris building up on the heat exchanger. Some banging noises could potentially be an indication that the pump – which pumps hot water from the boiler around the central heating system – is close to failing.


A sound not too far from banging is a clanging noise that could again be caused by loose pipework. Alternatively, it could mean that the boiler fan is being obstructed.


A buzzing noise could indicate that electrical components within the boiler are malfunctioning and likely need to be replaced. If the buzzing noise is coming from the thermostat then it could mean that the conductor is dirty and needs to be replaced


Boilers tend to have some operational noise that resembles a slight humming – for the most silent models look out for boilers that have been Quiet Mark accredited – but a loud humming could be the sign of a loose part (most likely the central heating pump).


Too much air within the pipes can cause blockages that prevent the water from circulating around the heating system. Should you be hearing this by a radiator then it's likely that they need to be bled.

We've covered more boiler noises in Why is My Central Heating So Noisy? to help you get to the cause of the problem.


6. Low boiler pressure

Boiler pressure is a measurement of the pressure of the hot water passing through the central heating system. Should the boiler pressure drop too low then the central heating will fail to work.

Your boiler will feature a pressure gauge that can be used to read the boiler pressure. If the needle is anywhere below 1 then the pressure is too low. Typically boiler pressure should sit somewhere between 1 and 2. However, you should consult the manufacturer's instructions to find the appropriate pressure for your boiler.

All boilers will very gradually lose boiler pressure over time but a sudden sharp drop could be the sign of a bigger issue. So if you've noticed a drop in boiler pressure check for water leaks and cold patches on radiators (as they may need bleeding).

Increasing boiler pressure is something you can do yourself although you shouldn't hesitate to contact an engineer if you need to. Visit our guide to What Causes Low Boiler Pressure? to find out how to increase boiler pressure in 8 simple steps.


7. Frozen condensate pipe

Condensing boilers have a condensate pipe which leads acidic water, produced as the boiler operates, away from the unit and down a drain. Many condensate pipes are external to the property which, as they contain liquid, can make them prone to freezing.

You can thaw out the condensate pipe yourself by pouring warm (not boiling) water over the frozen area.

Get your boiler back up and running using the steps in How to Thaw a Frozen Condensate Pipe.

To prevent the condensate pipe from freezing in future, your heating engineer may recommend lagging the pipe. Lagging simply means wrapping the pipe with insulation to keep it warmer and lower the risk of it freezing.


8. Radiators are cold

In the case that some of your radiators aren't heating up then there could be a build up of sludge or air in the system.

If only the bottom of your radiator is getting hot then you might need to bleed the radiator. This is fairly straightforward and doesn't require an engineer but if you don't feel comfortable doing it then contact a professional.

If certain radiators aren't getting hot then your radiators could need balancing. This can also be done without the help of an engineer but only if you feel confident doing it. The process involves adjusting the valves on all of the radiators in your property to ensure each is getting enough hot water to work effectively. Our guide on How to Balance Radiators can take you through the process.

Should you try bleeding and balancing your radiators but have no luck then you could well have an issue with sludge build up preventing a free flow of hot water to the radiators. A professional engineer can remove this build up by chemically cleaning or flushing the system, this is something that you shouldn't try yourself.


9. Boiler keeps switching itself off

A boiler could be constantly switching itself off for a number of reasons. Some of the key culprits are:

Low boiler pressure

Thermostat issues

Lack of water flow due to a closed valve or the pump not circulating the water around the system properly

Too much air within the system

A build up of sludge or other debris within the system


If the thermostat is working as it should and the boiler pressure is in line with the manufacturer's instructions then it's time to call a Gas Safe registered engineer.


10. Boiler is not responding to the thermostat

Pairing your boiler with a thermostat – particularly a smart thermostat – is a great way to increase the efficiency of your home. However, if your boiler isn't responding to the thermostat then it can be particularly frustrating.

Start by making sure the temperature on the thermostat is above the current room temperature.

If the boiler still doesn't respond after turning the room thermostat right up then it's time to look into the problem a little further:

Check it has a full charge and working batteries

Smart thermostats need to be connected to the internet so make sure your Wi-FI is running

Look through the temperature settings and daily schedules that may be preventing the heating from coming on.


How much does boiler repair cost?

Boiler repair costs will vary depending on the issue and rates charged by the engineer. They will vary greatly based on the problem and rates charged by the installer. You can save money by resolving certain boiler problems yourself. However, we must stress that the majority of boiler problems require the expertise of a Gas Safe registered engineer. Certain boiler problems should only be tackled by a Gas Safe registered engineer.

Depending on the fault and how frequently your boiler's running into trouble, a boiler replacement could be more cost effective.

Could you need a boiler replacement?

Sometimes it doesn't make financial sense to repair a boiler. Instead a boiler replacement would be much more cost-effective.

As boilers age, they become less reliable and are likely to need repairing more frequently. Those boiler repair bills will begin to add up and there comes a point where a boiler replacement is your best option.

Depending on the type of boiler being installed, new boiler installations costs can range from around £1,000 to £3,750, including installation. When you consider that certain replacement parts can cost several hundred pounds, it could be a wise move to make the longer term investment in a replacement boiler. Find out more in New Boiler Replacement Costs.

You should consider a boiler replacement if your boiler is over 8 years old, it's breaking down regularly, difficult for engineers to find replacement parts or your heating bills are on the rise.

Modern boilers are much more reliable than older units and will even be covered by a warranty period. A warranty will see that you're covered by the manufacturer in the event of a fault (terms and conditions permitting) which could save you money. In addition, a new boiler will increase the efficiency of your heating system, helping to lower your heating bills.

As with the vast majority of boiler repairs, a boiler replacement must be carried out by a Gas Safe registered engineer. Our network of heating engineers includes heating engineers right across the UK and we check their Gas Safe credentials on a daily basis. And it couldn't be simpler to connect with the engineers in your area.


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