Boiler Breakdown! An Engineer’s Step-by-Step Crisis

Your boiler has stopped working. No heating, no hot water, and possibly a worrying error code on the display. Before you panic, take a breath. This guide walks you through exactly what to do: safety checks first, simple fixes you can try yourself, when to call an engineer, and how to get help fast.

Step 1: Safety First (Do This Before Anything Else)

Before touching the boiler or trying any fixes, check for these two dangers:

Do you smell gas?

Natural gas has an artificial smell added (like rotten eggs) so you can detect leaks. If you smell this:

• Do not turn any lights or switches on or off
• Do not use your phone inside the property
• Do not smoke or create any flame or spark
• Do open windows and doors
• Do turn off the gas at the meter if you can do so safely
• Do get everyone (including pets) out of the property
• Do call the Gas Emergency Line from outside: 0800 111 999

This is a free 24-hour service. They will send someone to make the situation safe.

Is there a water leak?

If water is actively leaking from the boiler or nearby pipes:

• Turn off the water supply at the main stopcock (usually under the kitchen sink or where the mains enters your property)
• If the leak is severe, turn off the boiler at the isolator switch
• Place towels or containers to catch water and prevent damage
• Call an engineer

A small drip is not an emergency but should be investigated soon. A significant leak needs urgent attention.

If there is no gas smell and no major leak

You can safely proceed to the quick checks below.

Step 2: Quick Checks You Can Do Yourself

A surprising number of “breakdowns” are caused by simple issues you can fix in minutes. Before calling an engineer, run through these checks:

1. Check the power supply

Fuse box: Go to your consumer unit (fuse box). Has a switch tripped? The boiler circuit may have tripped due to a power surge or minor fault. Try resetting it. If it trips again immediately, you have an electrical fault that needs an engineer.

Isolator switch: There is usually a switched fused spur on the wall near the boiler. Make sure it is switched ON and the fuse has not blown.

Boiler itself: Some boilers have an on/off switch or button. Check it is on.

2. Check the thermostat

Batteries: If you have a wireless thermostat, check the batteries. Dead batteries are one of the most common causes of “boiler not working” calls. Replace them and wait a few minutes.

Temperature setting: Is the thermostat set high enough to call for heat? If the room is already at or above the set temperature, the boiler will not fire. Turn it up to maximum temporarily to test.

Mode: Is it set to heating, hot water, or both? Some thermostats have separate controls.

3. Check the timer/programmer

Is the heating actually scheduled to be on right now? Check your timer or programmer. If the clock has reset (after a power cut, for example), the schedule may be wrong.

Try setting it to “constant” or “always on” temporarily to test whether the boiler will fire.

4. Check the pressure

Look at the pressure gauge on your boiler (usually a dial or digital display on the front). It should read between 1 and 1.5 bar when the system is cold.

• Below 1 bar: Pressure is too low. The boiler may have locked out. You can try repressurising using the filling loop.
• Above 2.5 bar: Pressure is too high. Do not add more water. You may need to bleed a radiator to release some pressure.

For step-by-step instructions, see our guide to boiler pressure.

5. Try the reset button

Most boilers have a reset button (often marked with a flame symbol or “reset”). If the boiler has locked out due to a fault, pressing this may clear it and allow the boiler to restart.

Important: If you have to reset more than once or twice, there is an underlying fault. Do not keep resetting; call an engineer.

6. Check for a frozen condensate pipe (winter)

In cold weather, the condensate pipe (a plastic pipe that runs from your boiler to an outside drain) can freeze, causing the boiler to shut down.

Signs of a frozen condensate:

• Boiler stopped during or after cold weather
• Gurgling sounds from the boiler before it stopped
• Error codes relating to “condensate” or specific fault codes (varies by brand)

You can often thaw this yourself safely. See our frozen condensate pipe guide for step-by-step instructions.

Step 3: Understanding Error Codes

If your boiler has a digital display, it will usually show an error code when something is wrong. This code tells an engineer exactly what the boiler thinks is faulty.

How to find the error code

• Look at the boiler display. It may show a code like “F28”, “EA”, “E119”, etc.
• Some boilers show flashing lights instead of codes. Note the pattern.
• Write down the code exactly as displayed.

Common error codes by brand

Note: These are simplified explanations. The same code can have multiple causes. An engineer uses the code as a starting point for diagnosis.

For brand-specific fault code information, see our manufacturer help pages.

Common Causes of Boiler Breakdown

Understanding what typically goes wrong can help you describe the problem and know what to expect.

Most common causes

Winter-Specific Issues

Boilers work hardest in winter and this is when most breakdowns occur. Some issues are specifically winter-related:

Frozen condensate pipe

The most common winter breakdown. The condensate pipe runs outside and can freeze in temperatures below zero. The ice blocks the pipe, and the boiler shuts down for safety.

This is usually fixable yourself by thawing the pipe with warm (not boiling) water. See our frozen condensate guide.

Increased demand exposing weak points

Components that were marginal during mild weather may fail when the boiler runs constantly in cold weather. Pumps, fans, and heat exchangers that were “just about coping” can give up under sustained load.

Pressure fluctuations

Heating systems expand and contract more dramatically in cold weather. If your system has a slow leak or the expansion vessel is failing, you may notice pressure drops more in winter.

What you can do

• Get your boiler serviced before winter (autumn is ideal)
• Know where your condensate pipe is and how to thaw it
• Keep an eye on pressure during cold spells
• Have an engineer’s number saved in your phone

When to Call an Engineer

Call a Gas Safe registered engineer if:

• You smell gas (call Gas Emergency first: 0800 111 999)
• The quick checks above did not fix the problem
• You have to keep resetting the boiler (more than once or twice)
• The boiler is making unusual noises (banging, kettling, whining)
• There is a water leak you cannot stop
• You see an error code you cannot clear
• You are not comfortable doing any checks yourself

Do not attempt to open the boiler casing or work on gas components yourself. This is illegal and dangerous.

What to Tell the Engineer When You Call

The more information you provide, the faster we can help. When you call, have this ready:

Essential information

• Boiler make and model: Found on the front of the boiler or on a sticker inside the casing flap (e.g., “Worcester Bosch Greenstar 30i”, “Vaillant ecoTEC plus 832”)
• Error code: Write it down exactly as shown
• What happened: Did it stop suddenly? Gradually? After a noise?
• What you have tried: Mention if you have checked power, pressure, reset, etc.
• Your location: Postcode helps us dispatch the nearest engineer

Example call script

“Hi, my boiler has stopped working. It’s a Vaillant ecoTEC plus 832, showing error code F28. I’ve checked the power and thermostat, and the pressure is showing 1.2 bar. I’ve tried resetting once but it came back with the same code. I’m in N1, Islington. Are you available for an emergency callout?”

This tells us everything we need: the boiler, the fault, what you have checked, and where you are. We can often start thinking about likely parts before we even arrive.

While You Wait for the Engineer

Stay warm

• Use electric heaters if you have them (safely)
• Close doors to keep heat in occupied rooms
• Layer up with warm clothing and blankets
• If you have vulnerable people (elderly, very young, unwell), consider whether they need to stay elsewhere temporarily

Hot water alternatives

• If you have an immersion heater in your hot water cylinder, switch it on
• Boil a kettle for washing
• Ask a neighbour if you can use their shower in an emergency

Prepare for the engineer

• Clear the area around the boiler so they can work
• Make sure they can access the loft if you have a tank up there
• Have your boiler manual ready if you have it
• Note down any warranty information

What to Expect When the Engineer Arrives

Knowing what happens during a callout can reduce anxiety and help you understand the process.

Initial assessment

The engineer will:

• Ask you to describe the problem and what you have noticed
• Check the error code and boiler display
• Run initial diagnostic tests
• Inspect visible components

Diagnosis

Using the error code, symptoms, and their experience, the engineer will identify the likely fault. Sometimes this is quick and obvious; sometimes it requires more investigation.

Explanation and quote

A good engineer will explain:

• What they think is wrong
• What needs to be done to fix it
• Whether they have the part or need to order it
• How long the repair will take

You should receive a clear explanation before any chargeable work begins.

Repair

If the engineer has the part and you approve the work, they will carry out the repair, test the system, and ensure everything is working correctly.

Paperwork

You should receive documentation of what was done, any parts fitted, and relevant safety certificates if gas work was involved.

Preventing Future Breakdowns

The best breakdown is the one that never happens. Here is how to reduce your risk:

Annual servicing

The single most effective prevention. A service catches worn components before they fail, clears debris, checks safety, and keeps your warranty valid. Book it every year, ideally before winter.

Magnetic system filter

A filter on the return pipe catches sludge and debris before it reaches the boiler. This protects internal components and extends boiler life. If you do not have one, consider adding it.

Inhibitor

Chemical inhibitor in your heating system prevents corrosion and sludge formation. It should be topped up at each service.

Know your system

• Know where the stopcock is
• Know where the gas meter and emergency shutoff is
• Know how to repressurise your boiler
• Know where the condensate pipe runs (for winter thawing)

Do not ignore warning signs

Strange noises, fluctuating pressure, intermittent problems: these are warnings. A small repair now is cheaper than an emergency later. See our guide to boiler noises.

Frequently Asked Questions