Boiler Not Working? Most Common Problems (And Fixes)

Boiler not working? Start with these checks

If your boiler has stopped working, there are a few common issues you can check safely before calling an engineer.

• Check whether the boiler has power and whether the fused spur or circuit breaker has tripped.

• Check the pressure gauge. If it is below around 1 bar, the boiler may need repressurising.

• Check the thermostat and timer settings to make sure they are calling for heat.

• Check whether the condensate pipe has frozen during cold weather.

• Make sure your gas supply is working and that a prepayment meter has sufficient credit.

Important: Do not attempt to open or repair the boiler yourself. If you smell gas, suspect carbon monoxide, or notice signs of a serious fault, turn the appliance off if it is safe to do so, leave the property, and contact the appropriate emergency service or a Gas Safe registered engineer immediately.

Most boiler faults are caused by power issues, low pressure, thermostat settings, frozen condensate pipes, or component failures. The sections below will help you identify the most common causes and what to do next.

Three key takeaways

• Most boiler faults can be traced to power issues, low pressure, thermostat settings, or frozen condensate pipes.

• Symptom-based troubleshooting can help identify the likely cause before calling an engineer.

• Gas leaks, carbon monoxide concerns, and internal boiler faults should always be handled by a Gas Safe registered engineer.

Boiler has no power or a blank display

If your boiler display is completely blank or there are no lights showing, the issue may be related to the electrical supply rather than the boiler itself.

Start by checking whether a circuit breaker has tripped in your consumer unit. You should also check the fused spur near the boiler, as a blown fuse can prevent the appliance from receiving power.

If there has recently been a power cut, some boilers may require a manual reset before they begin operating normally again.

Prepayment meters can also cause unexpected shutdowns if credit has run out.

If the display remains blank after these checks, work through our guide to boiler has no power or a blank display.

Boiler will not turn on or fire up

If your boiler has power but refuses to start, there are several possible causes.

Low system pressure is one of the most common. Most boilers require pressure of around 1 to 1.5 bar to operate correctly. If the pressure falls too low, the boiler may enter a safety lockout mode.

Thermostat settings, timer schedules, and failed reset attempts can also prevent a boiler from firing up.

Some boilers display fault codes when an ignition problem occurs, while others may repeatedly attempt to start before shutting down.

If your boiler still refuses to operate after checking these areas, see our guide to boiler will not turn on for more detailed troubleshooting advice.

No hot water but the heating works

If your radiators are heating normally but there is no hot water from your taps, the fault may be isolated to the hot water side of the system.

On combi boilers, a faulty diverter valve is a common cause. This component directs heated water either to your taps or your radiators. If it becomes stuck or develops a fault, hot water production may be affected.

Other possibilities include temperature sensor issues, faulty thermostats, or internal component failures.

The exact cause will depend on the boiler model and the symptoms being displayed.

If you own a Worcester Bosch appliance, our guide to Worcester Bosch boiler no hot water may help identify the issue.

No heating but the hot water works

When hot water is available but the heating remains off, the problem is often linked to controls rather than the boiler itself.

Start by checking that your thermostat is calling for heat and that your heating schedule is active. If you use smart controls, ensure they have not lost connection after a power cut or software update.

Zone valves, motorised valves, and heating controls can also prevent heat from reaching your radiators even when the boiler itself is working correctly.

Before arranging a repair, it is worth checking the thermostat batteries, timer settings, and heating programme.

Boiler is leaking

A leaking boiler should never be ignored.

Even a small leak can lead to pressure loss, reduced performance, and damage to nearby electrical components.

Leaks may be caused by worn seals, corroded pipework, faulty valves, loose connections, or internal component failures.

In some cases, homeowners notice that the boiler pressure keeps falling before they identify the leak itself.

If you can safely see water around the appliance, isolate the area and monitor the leak, but do not remove the boiler casing.

Our guide explains why a boiler is leaking and the steps you should take next.

Boiler keeps losing pressure

If you find yourself regularly topping up your boiler pressure, there is usually an underlying issue that needs investigating.

Pressure can drop naturally after bleeding radiators, but repeated pressure loss often points to a leak somewhere within the heating system or a fault with an internal component.

Common causes include:

• Leaks from radiators, valves, or pipework

• A faulty pressure relief valve

• Problems with the expansion vessel

• Internal boiler leaks

If the pressure drops occasionally and then remains stable, the issue may be minor.

However, pressure that continually falls below the recommended level should be investigated by a qualified engineer.

Our guide explains the most common reasons a boiler keeps losing pressure and what checks you can carry out safely.

Boiler is showing an error code

Most modern boilers use fault codes to identify specific problems.

These codes help engineers diagnose faults more quickly and can sometimes indicate whether the issue is related to pressure, ignition, sensors, circulation, or electrical components.

If your boiler is displaying a fault code:

• Make a note of the code

• Check your user manual

• Follow any manufacturer guidance

• Avoid repeatedly resetting the boiler

Repeated resets can sometimes make diagnosing the fault more difficult and may place additional strain on components.

If the fault persists after basic troubleshooting, it is usually best to arrange a professional inspection.

Brand-specific boiler problems

The exact checks you should carry out can vary depending on the boiler manufacturer and model.

Different brands use different fault codes, controls, safety systems, and troubleshooting procedures.

For model-specific guidance, see our dedicated troubleshooting articles:

• Vaillant boiler not working

• Baxi boiler with no error code

• Glow-worm boiler not firing up

• oil boiler not firing up

Some faults may also be linked to specific controls rather than the boiler itself.

If you suspect the issue is related to heating controls, our guides to Hive thermostat problems and boiler fan problems may help identify the cause.

How to help prevent boiler breakdowns

While no boiler is completely immune to faults, regular maintenance can significantly reduce the likelihood of unexpected breakdowns.

Annual servicing allows a Gas Safe engineer to inspect safety components, check combustion performance, identify wear and tear, and ensure the appliance is operating efficiently.

Homeowners can also take simple preventative measures throughout the year.

These include:

• Maintaining the correct boiler pressure

• Bleeding radiators when required

• Protecting external condensate pipes during winter

• Using inhibitor to reduce corrosion within the heating system

• Installing a magnetic filter to help capture debris and sludge

Preventative maintenance cannot eliminate every fault, but it can often identify small problems before they develop into expensive repairs.

Should you repair or replace your boiler?

Not every boiler fault means a replacement is needed.

Many common issues, including low pressure, thermostat faults, frozen condensate pipes, and ignition problems, can often be repaired quickly and cost effectively.

However, replacement may be worth considering if:

• Your boiler is more than 10 to 15 years old

• It breaks down frequently

• Replacement parts are becoming difficult to source

• Repair costs are increasing

• The appliance is becoming less efficient

Modern A-rated boilers are typically more efficient than older models and can provide more reliable performance.

If you're unsure whether to repair or replace your boiler, our guide explains the factors to consider before making a decision.

Should I repair or replace my boiler?

The answer depends on the age of the boiler, the cost of repairs, the availability of replacement parts, and the overall condition of the system.

Newer boilers are often worth repairing, while older appliances with recurring faults may be better replaced.

For a more detailed comparison, see our guide on whether to repair or replace your boiler.

Need a new boiler?

If your boiler has reached the end of its lifespan or repeated repairs are becoming uneconomical, replacing it with a modern, energy-efficient model could reduce running costs and improve reliability.

At iHeat, you can compare leading boiler brands online and receive a fixed installation quote in minutes.

With next-day installation available in many areas and flexible payment options, replacing an unreliable boiler can be quicker and simpler than many homeowners expect.

Get your fixed online quote today and find the right boiler for your home.