A boiler not working can mean no heating, no hot water or a system that repeatedly switches itself off. This guide explains the most common boiler problems, the checks you can safely make and when professional diagnosis is needed.
A boiler that suddenly stops working can quickly become a major inconvenience, particularly during colder weather.
Some faults are relatively simple, such as incorrect thermostat settings or low system pressure. Others can involve ignition, circulation, heating controls or components inside the boiler.
Modern boilers are designed to shut down when they detect certain faults, so a boiler that has stopped working is not necessarily completely broken.
The fault code, pressure reading and symptoms around the heating system can often provide useful clues about what is happening.
Below are some of the most common reasons a boiler may stop providing heating or hot water.
Before assuming that the boiler itself has developed a serious fault, there are several simple things worth checking.
Start by looking at the boiler display. Modern boilers may display:
Write down any fault code before resetting or changing anything. The code can help identify which part of the system may need further investigation.
Also check whether the problem affects:
This distinction can provide an important clue to the underlying fault.
Several different problems can result in a boiler failing to operate normally. The following are among the most common.
Low system pressure is a common reason for a boiler to stop operating.
Many sealed heating systems normally operate at approximately 1 to 1.5 bar when cold, although the correct pressure depends on the boiler manufacturer and model.
If pressure falls too low, the boiler may display a warning or lock itself out.
A one-off pressure adjustment may solve the immediate problem, but pressure that repeatedly drops can indicate:
If your pressure keeps falling, read our guide:
Why Is My Boiler Losing Pressure?
It sounds simple, but an electrical supply problem can sometimes make a boiler appear completely dead.
Check whether:
If a breaker repeatedly trips when the boiler operates, do not continue resetting it. The underlying electrical or boiler fault should be investigated.
Sometimes the boiler itself is working correctly but is not receiving a request for heating.
Check:
Try setting the thermostat several degrees above the current room temperature and check whether the boiler responds.
Gas boilers need to ignite correctly in order to heat water.
If ignition fails, the boiler may attempt to start several times before displaying a fault code or entering lockout.
Possible causes can include problems with:
These are not suitable DIY repairs. If the boiler repeatedly fails to ignite, professional diagnosis is required.
Condensing boilers produce water that normally drains away through a condensate pipe.
During very cold weather, an external section of this pipe can sometimes freeze.
A blocked condensate pipe may cause the boiler to stop and display a fault code.
If the pipe is easily accessible and the manufacturer’s instructions provide a safe thawing procedure, follow those instructions carefully.
Never use boiling water on frozen pipework.
A boiler may be producing heat correctly while another part of the central heating system prevents it from circulating effectively.
Possible causes include:
A common symptom is some radiators remaining cold while others heat normally.
Boilers contain numerous components that can eventually wear or fail.
Depending on the boiler, problems may involve components such as:
A fault code may help narrow down the problem, but internal boiler components should be inspected by an appropriately qualified engineer.
There are several basic checks homeowners can perform without opening or dismantling the boiler.
Look for an error or fault code. Make a note of it and check the boiler manufacturer’s user manual for its meaning.
Look at the pressure gauge or digital pressure reading. If pressure is significantly below the recommended range, the boiler may not operate correctly.
Make sure:
Make sure the boiler has power and that its isolation switch has not accidentally been turned off.
Look around:
Visible leaking water should be investigated.
A boiler that starts normally but repeatedly switches itself off may be reacting to another fault.
Possible causes include:
Pay attention to when the boiler shuts down.
For example, does it stop:
These details can help an engineer diagnose the problem more quickly.
Modern boilers monitor many aspects of their operation.
When the boiler detects a problem, the display may show a letter, number or combination of both.
Fault codes can relate to issues such as:
The meaning of a fault code varies between manufacturers and boiler models.
Always check the manufacturer’s instructions for your particular boiler.
A fault code can help identify the area that requires investigation, but it does not necessarily mean the component mentioned by the code automatically needs replacing.
Proper diagnosis is still important.
Many boilers have a reset function that can clear a temporary lockout.
If the manufacturer’s instructions specifically recommend resetting the boiler for the displayed fault, follow those instructions.
However, repeatedly resetting a boiler that continues to lock out is not a repair.
If the same fault returns, there is usually an underlying reason that needs attention.
Professional boiler diagnosis is advisable when:
Do not remove the boiler casing or attempt repairs involving internal gas components yourself.
Gas boiler repairs and work involving gas-related components should be carried out by an appropriately qualified Gas Safe registered engineer.
Not every boiler fault can be prevented, but regular maintenance can help identify developing issues before they cause a complete breakdown.
Useful steps include:
A boiler that repeatedly develops the same problem should be diagnosed rather than continually reset or topped up.
TES Heating provides boiler diagnostics, heating repairs and plumbing services across London.
If your boiler is not working, the boiler and connected heating system can be checked to identify the cause before the appropriate repair is recommended.
Whether the problem involves pressure loss, ignition, heating controls, radiators or another central heating fault, identifying the actual cause first can help avoid unnecessary replacement of components.
For more information about our services, visit our
Plumbing & Heating Services in London.
A boiler can stop operating because of low pressure, electrical supply problems, thermostat settings, ignition failure, circulation problems or an internal fault. Check the display for a fault code before making any changes.
Possible causes include thermostat settings, circulation problems, radiator valves, trapped air, sludge, pump problems or another central heating fault.
If the boiler manufacturer specifically recommends a reset for the displayed fault, follow the user manual. If the boiler repeatedly locks out after resetting, the underlying problem should be investigated.
If hot water works but the radiators remain cold, the issue may involve heating controls, thermostat settings, circulation, valves or another part of the central heating system.
Call an appropriately qualified Gas Safe registered engineer when the boiler repeatedly fails, displays recurring faults, leaks, will not ignite or requires work involving internal gas components.
