Most Common boiler fualts

Common Boiler Faults And How To Identify Them

When the boiler of your fails, it can be a severe inconvenience at the best of times. The good news is that problems with a boiler unit are easily addressed by a professional and many of these issues can be repaired by anyone with a small amount of introduction to the task.  

 To make troubleshooting these errors a simple task, most modern boilers feature a display screen where a digital code will allow you to know exactly what sort of issue you are facing.  

picture of a hand turning the switch on the front of a central heating combi boiler


Here are some of the most common types of boiler errors.  


Common Boiler Problems: 

Hot water but no heating 

No heating or hot water 



Noises coming from the boiler  

Low-pressure in the boiler

Radiators are cold 

Frozen condensate pipe 

Boiler is not responding to the thermostat 

Boiler keeps switching itself off 



1.Hot water but no heating 


 The boiler is designed to provide the home with heat as well as hot water for domestic use. If you have found that hot water is available from the taps but the central heating is not working, then you can bet there is a problem.  

If you notice there is a problem with your central heating, then you should begin by checking if the pressure in your boiler is too low.  

Thermostats allow you to adjust the desired temperature of your central heating as well as the timing for activation and deactivation. If the heating hasn’t turned on in the time you planned, it is time to check those thermostat settings again.  

Boiler pressure describes the pressure of the hot water making its way through your central heating system. If the pressure drops too low, the central heating will fail.  

Increasing the pressure of your boiler is a fairly simple procedure that can be done without the assistance of a heating engineer. But if you feel even slightly unsure about the process, it would probably be best to call in the professionals.  

Thermostat errors and boiler pressure are not the only reasons that you will have problems with your boiler and hot water supply. But, if your problems are not connected to boiler pressure or thermostat adjustments, things get a little more complex.  

If your thermostat is working fine and the pressure of your boiler is at the correct level the error may need professional boiler repair. Some of the more common reasons that can cause heating to fail while hot water seems to be working well is an issue with the diaphragms, airlocks or the motorised valves.  

If your heater system includes a combi boiler, you could be looking at a problem with the diverter valve. A combi boiler provides heating to the home and hot water on demand. It is the diverter valve that directs the hot water where it is needed, this could be to the hot water outlets or the radiators. If this diverter valve fails to function properly, you will either be stuck with no hot water in the outlets or no central heating.  

If your problem is not related to the boiler pressure or thermostat settings, a Gas Safe registered engineer will be able to provide assistance in changing the airlocks, diaphragms, diverter valves and motorised valves. They will also be able to carry out necessary repairs and replace anything that has become broken.  


2. No heat or hot water 

In an ideal situation, you should be able to rely on your boiler to keep your house arm and provide you with hot water. If you see that these functions are not working, you will need to get this fixed as soon as possible. 

There is no one single issue that can cause these important functions to fail. So, before you begin assigning the fault to one single component, the first thing to check is that the power to your boiler has not become interrupted.  

If there are no interruptions in the boilers power supply, then we will have to begin looking into other possible issues. Your boiler will typically display a code that can indicate where the problem is located. Here are some of the possible errors you can expect.  


fuel is not provided properly — if you are running a gas boiler, check that the fuel line is unobstructed. If your boiler is running on oil, make sure that the fuel in the tank is replenished. 

Thermostat — check that the thermostat settings are at the right temperature and higher than the current temperature of the room.  

Freezing — if the condensate pipe has frozen over, it will need to be thawed out properly, we will cover this point further in the article.  

Low boiler pressure — as mentioned, if the pressure of the boiler is low, it will need to be reset. You can find detailed instructions on how to do this in the owner’s manual.  


3.Boiler is leaking 

If your boiler is leaking, you can bet that this is a bad sign. The cause and effect of the leak will depend on where it is located along the central heating system.  

Before you try to stop the leak, turn off the water supply and shut down the central heating. It should be pointed out here that repairing a leaking should only be attempted by a registered Gas Safe Engineer. 

 The most common cause of a leaking boiler will be some internal component like a pump seal or a pressure valve. If the link is coming from a pressure valve, the boiler pressure could be too high. If the leak is located in a pump seal this could be a sign that it is worn out and needs replacing.  


4.Boiler is kettling 

If you hear a strange sound of rumbling coming from your boiler, something like the sound of a kettle heating up, this is an indication of another common problem. Lime scale deposits can collect on your heat exchanger (the coils that transfers the heat from the source of fuel to the water) this problem is commonly referred to as kettling.  

When debris accumulates in your boiler, the water within the heat exchange can become obstructed. This can cause the water that does pass through the exchange to overheat, turn to steam and begin making funny noises.  

This is a more common problem in areas that receive hard water, but it is not uncommon in areas that receive soft water either. Not only does this place strain on the boiler but it can shorten the service life of the entire system. 

If you notice a kettling issue in your boiler, the best course of action will be to call in a professional Gas Safe Registered engineer. The engineer will remove the build-up and ensure the system is restored to full function.



5.Noisy Boiler

There are many various forms of Boiler noises. It can be banging noise, whistling, gurgling, and others. All these noise types originate through various reasons, and a sign of different faults.  For this reason, anytime you hear any kind of noise in the heating system or boiler, never ignore it - it could be a sign of fault. 

It is important to note that fault varies based on the type of sound produced and the place it is coming from. Below is a shortlist of common types of sounds produced by the boiler, which will help you determine the cause.  


  • Banging Noise – Often, a banging noise is caused by an internal component or the pipework. However, it can also be caused as a result of debris build up on the heat exchanger. It can also be an indication of a faulty pump that pumps hot water from the boiler to the heating system.  


  • Whistling Noise – This whistling sound closely resembles that of a kettle when water is boiling. The sound is caused by a build-up of debris in the heat exchanger.  


  • Buzzing Noise – This noise is often a clear indication that electrical components within the boiler are faulty. The noise could be originating from the thermostat, which is a sign that the conductor is either dirty or it needs replacing. 


  • Clanking Noise – This sound is closely similar to a banging noise, and it may be caused by loose pipework. It could also mean that the boiler fan is being obstructed by an object.  


  • Gurgling Noise – Did you know that too much air within the pipes can prevent water from circulating through the heating system? Whenever there is too much air in a system, you will hear a gurgling sound – especially when it is coming from the radiator. The solution is bleeding the system.  


  • Humming Noise – The truth is that a boiler tends to hum while it is in operation. Although the humming is slight, if you are looking for the most silent models, look for those with a Quiet Mark accreditation. Nevertheless, if the humming is loud, then it is a sign of loose parts -  mainly the central heating pump.  


6.Low Boiler Pressure 


Whenever water gets hot, it increases in pressure. As such, boiler pressure simply refers to the pressure of hot water passing through the central heating system. The central heating will fail to work if the boiler pressure is too low. 

Boilers always come with a pressure-measuring gauge that anyone can use to read the pressure in the boiler. Therefore, anytime you get a reading below the 1 mark, automatically know the pressure is too low. The boiler pressure should always sit somewhere between the 1 and 2. Nevertheless, it is wise to consult the boiler manufacturers guide to know the appropriate pressure for your system.

It is important to note that as the boiler ages, it gradually loses its pressure. However, a sudden pressure drop is a big problem and a sign of fault. For this reason, if you identify a pressure drop, automatically know that you have a water leak. 

The good news is that increasing boiler pressure is a task anyone can do for themselves. However, it is wise to consult a professional. 


7.Frozen Condensate Pipe 


Condensing boilers are featured with a condensate pipe whose primary function is to drain Acidic water away from the unit. It is important to note that as the boiler is working, it creates acidic water. Since these pipes drain acidic water away from the unit, they are susceptible to external elements such as freezing. 

It is paramount to thaw out the condensate pipe during winter or when you are living in frozen areas by pouring warm water on it. 

 To prevent future freezing, professionals recommend lagging the pipe. What does lagging mean? It simply means wrapping it with insulation to keep it warm. 


8.Cold Radiator 

When a radiator is not heating up, it means that it is either clogged with sludge or there is air in the system. If you start noticing the bottom of the radiator is getting warm/hot, and the top is not - then you should consider bleeding it. This is a straightforward procedure that does not need the help of a professional. However, if you do not know how to go about it, consult a professional. 

If you try balancing or bleeding the radiator; and you still notice no change, then the chances are that it has a sludge build-up, which is preventing the free flow of hot water to the radiator. A professional will help you clear the sludge through chemical cleaning and flushing the system. You should never try doing this yourself. 


9.Boiler Constantly Switching Itself Off 


There are several reasons why a boiler could switch itself regularly. Some of the common reasons are: - 


  • A build-up of sludge or debris in the system 
  • Too much air in the system 
  • Thermostat issues 
  • Low boiler pressure 
  • Lack of water flow (either due to a closed valve or pump issues) 


If the thermostat is working as required and the boiler has the required pressure as per the manufacturer's guideline, then you should contact a Gas Safe Registered engineer.


10.Boiler Not Responding To The Thermostat 


One of the best ways to increase efficiency at home is combining a thermostat with the boiler (especially a smart thermostat).  However, when the boiler fails to respond to the thermostat, it can be frustrating. 


To diagnose the problem, start by ensuring the temperature on the thermostat is above the current room temperature. If the boiler is still not responding to the thermostat, then diagnose the problem further by: - 


  • Checking if the thermostat has a working battery or if it is fully charged 
  • If you have a smart thermostat, ensure it is connected to the internet 
  • Go through the temperature settings  


How Much Does A Boiler Repair Cost? 

The truth is that the cost of repairs will vary based on fault, professional rates, and the number of faults a boiler has. You can always save some money by doing some boiler maintenance by yourself. However, never try to tackle major boiler problems, it is wise to call a professional. Also, the cost of any part that needs replacing will affect the cost of repairing a boiler. To defiantly know the cost, consider talking to a professional.

If you are experiencing any of the above problems below is a list of the areas we service

Heat Quick Direct Boiler Repairs & Service Cover All These Areas

Boiler Repairs & Service Central London | Boiler Repairs & Service Bond Street W1 | Boiler Repairs & Service Regent Street W1 | Boiler Repairs & Service Oxford Street W1 | Boiler Repairs & Service Soho W1 | Boiler Repairs & Service Chinatown W1 | Boiler Repairs & Service Harley Street W1 | Boiler Repairs & Service Marylebone W1 | Boiler Repairs & Service Mayfair W1 | Boiler Repairs & Service Piccadilly W1 | Boiler Repairs & Service SavileRow W1 | Boiler Repairs & Service Tottenham Court Road W1 | Boiler Repairs & Service Paddington W2 | Boiler Repairs & Service Bayswater W2 | Boiler Repairs & Service Hyde Park W2 | Boiler Repairs & Service Acton W3 | Boiler Repairs & Service Chiswick W4 | Boiler Repairs & Service Gunnersbury W4 | Boiler Repairs & Service Ealing W5 | Boiler Repairs & Service Hammersmith W6 | Boiler Repairs & Service Ravenscourt Park W6 | Boiler Repairs & Service Kensington W8 | Boiler Repairs & Service Holland Park W8 | Boiler Repairs & Service Maida Vale W9 | Boiler Repairs & Service North Kensington W10 | Boiler Repairs & Service Ladbroke Grove W10 | Boiler Repairs & Service Notting Hill W11 | Boiler Repairs & Service Shepherds Bush W12 | Boiler Repairs & Service West Kensington W14 | Boiler Repairs & Service Kensington Olympia W14 | Boiler Repairs & Service Bloomsbury WC1 | Boiler Repairs & Service St Pancras WC1 | Boiler Repairs & Service Russell Square WC1 | Boiler Repairs & Service Grays Inn WC1 | Boiler Repairs & Service High Holborn WC1 | Boiler Repairs & Service Kings Cross WC1 | Boiler Repairs & Service Drury Lane WC2 | Boiler Repairs & Service Aldwych WC2 | Boiler Repairs & Service Covent Garden WC2 | Boiler Repairs & Service Leicester Square WC2 | Boiler Repairs & Service Charing Cross WC2 | Boiler Repairs & Service Regents Park NW1 | Boiler Repairs & Service Baker Street NW1 | Boiler Repairs & Service Camden Town NW1 | Boiler Repairs & Service Primrose Hill NW1 | Boiler Repairs & Service Cricklewood NW2 | Boiler Repairs & Service Golders Green NW2 | Boiler Repairs & Service Hampstead NW3 | Boiler Repairs & Service Belsize Park NW3 | Boiler Repairs & Service South Hampstead NW3 | Boiler Repairs & Service Swiss Cottage NW3 | Boiler Repairs & Service St Johns Wood NW8 | Boiler Repairs & Service Primrose Hill NW8 | Boiler Repairs & Service Lisson Grove NW8 | Boiler Repairs & Service Whitehall SW1 | Boiler Repairs & Service Belgravia SW1 | Boiler Repairs & Service Pimlico SW1 | Boiler Repairs & Service Victoria SW1 | Boiler Repairs & Service Eaton Square SW1 | Boiler Repairs & Service Sloane Square SW1 | Boiler Repairs & Service St James SW1 | Boiler Repairs & Service Knightsbridge SW1 | Boiler Repairs & Service Chelsea SW3 | Boiler Repairs & Service Brompton SW3 | Boiler Repairs & Service Knightsbridge SW3 | Boiler Repairs & Service Earls Court SW5 | Boiler Repairs & Service Fulham SW6 | Boiler Repairs & Service South Kensington SW7 | Boiler Repairs & ServiceKnightsbridge SW7

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Heat Quick Direct are Vaillant accredited engineers

Heat Quick Direct is accredited by all the major gas boiler trade bodies, such as Gas Safe and we are approved G3 unvented hot water storage engineers approved by Worcester as accredited engineers and we are approved advanced Vaillant engineers.