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Your boiler’s stopped working, the heating’s gone cold, or there’s a strange noise coming from the cupboard. Boiler faults are frustrating, but they’re also incredibly common in UK homes—and many have straightforward fixes.
Understanding what’s gone wrong helps you decide whether it’s something you can sort yourself or whether you need a Gas Safe engineer. Either way, knowing what you’re dealing with takes the stress out of the situation.
Let’s walk through the most common boiler faults, what causes them, and what you can actually do about them.
A boiler fault is anything that stops your boiler working as it should. That might mean no heating, no hot water, error codes on the display, strange noises, or the boiler switching itself off repeatedly.
Modern boilers have safety controls built in. When they detect a problem—low pressure, overheating, circulation issues—they shut down to protect themselves and your home. That’s why your boiler displays an error code rather than just struggling on.
Boiler faults happen for three main reasons: age and wear, lack of maintenance, or problems elsewhere in your heating system. A well-maintained boiler in good condition can run for years without issues. An older system that’s never been serviced? You’re more likely to see faults appearing regularly.
Some boiler faults appear far more often than others. These are the ones heating engineers see day in, day out across UK homes.
Low Boiler Pressure
Low pressure is the single most common boiler fault. Your heating system should maintain between 1 and 1.5 bar when cold. Drop below 0.5 bar and most boilers shut down and display an error code—often F22 on Vaillant boilers or E119 on Worcester Bosch models.
Pressure drops gradually over time through normal operation. Bleeding radiators, small leaks, or natural evaporation all reduce system pressure. In many cases, topping up the pressure solves the problem immediately.
If pressure drops repeatedly—weekly or even daily—you’ve got a leak somewhere that needs finding and fixing. This is when you need professional help.
No Heating or No Hot Water
Losing heating, hot water, or both is another frequent fault. Sometimes you’ll have hot water but no heating, or heating but no hot water. Other times, everything stops working.
Partial loss—one working, one not—often points to a faulty diverter valve, which directs hot water either to your radiators or your taps. Complete loss suggests boiler pressure problems, thermostat issues, or the boiler itself isn’t firing.
Frozen condensate pipes in winter cause sudden complete loss of heating and hot water. The pipe freezes, the boiler detects a blockage, and shuts down. This is fixable but needs doing carefully to avoid damaging the pipe.
Boiler Keeps Turning Off
If your boiler fires up then shuts down after a few minutes, it’s detecting a fault and protecting itself. This cycling behaviour frustrates homeowners because the boiler seems to work briefly before giving up.
Common causes include low pressure, circulation problems from a failing pump, thermostat issues, or overheating from restricted flow. The boiler tries to operate, detects something’s wrong, and shuts off as a safety measure.
Repeatedly resetting the boiler doesn’t fix this—you need to identify why it’s shutting down. That usually requires a Gas Safe engineer with diagnostic equipment.
Strange Noises From the Boiler
Banging, whistling, humming, or gurgling noises from your boiler all indicate different problems. Loud banging (called kettling) happens when limescale or sludge builds up on the heat exchanger, causing localised boiling.
Whistling often points to restricted water flow or air in the system. Humming might be a failing pump. Gurgling suggests air pockets or low water levels.
Noises don’t always mean immediate danger, but they shouldn’t be ignored. They’re your boiler telling you something’s wrong before it fails completely.
Radiators Not Heating Properly
When some radiators stay cold while others heat up fine, you’ve got a circulation or balance problem rather than a boiler fault specifically. Still, homeowners often think the boiler’s broken.
Cold spots at the bottom of radiators suggest sludge build-up. Cold tops usually mean trapped air. If radiators furthest from the boiler stay cold, your system might need balancing or there’s restricted flow.
These issues affect your boiler’s performance even though the fault lies elsewhere in your heating system. Solving them often requires professional cleaning or balancing work.
Before booking a Gas Safe engineer, you can safely check a few things yourself. These basic checks take minutes and might solve the problem.
Check the Boiler Pressure Gauge
Find the pressure gauge on your boiler—either a dial with a needle or a digital display. Check it when the heating’s been off for at least an hour.
If it’s below 1 bar, your pressure’s too low. Most boilers have a filling loop underneath that lets you top up the pressure. Follow the instructions in your boiler manual or look for a guide specific to your boiler model online.
If pressure’s fine but you’re still getting faults, the problem lies elsewhere. If topping up pressure solves it but the fault returns within days, you’ve got a leak that needs professional attention.
Look for Visible Leaks or Drips
Walk around your home checking radiators, visible pipes, and the boiler itself for signs of water. Even small drips cause pressure loss and boiler faults over time.
Common leak spots include radiator valves, pipe joints under radiators, the pressure relief valve on your boiler (usually a copper pipe running outside), and automatic air vents on radiators or pipework.
Sometimes leaks are tiny—they weep slowly and evaporate before you notice puddles. Look for rust marks, damp patches, or discolouration around valves and joints.
Check the Thermostat and Programmer
This sounds obvious, but heating engineers are called out surprisingly often for thermostat issues rather than actual boiler faults. Check your thermostat’s set higher than the current room temperature. Verify your programmer’s set to “on” or “auto” rather than “off.”
Battery-powered thermostats can stop working when batteries die. Digital programmers occasionally lose their settings during power cuts. These simple issues look like boiler faults but solve themselves once you spot them.
If you’ve got a smart thermostat, check the app hasn’t been set to “away mode” or had its schedule accidentally changed.
Some problems you can handle yourself. Others need a Gas Safe registered engineer, both for safety and to avoid making things worse.
Call an engineer if you smell gas—that’s an emergency requiring immediate action. Turn off the gas at the meter and call the National Gas Emergency Service on 0800 111 999.
If your boiler’s displaying error codes you can’t clear by topping up pressure or resetting, professional diagnosis is needed. Modern boilers have dozens of sensors and components that only qualified engineers can safely test and repair.
Repeated problems—faults that keep coming back despite your fixes—signal underlying issues that need proper diagnosis. Resetting the boiler daily isn’t a solution; it’s delaying the inevitable breakdown.
Water leaks, component failures, strange noises that don’t stop, and complete loss of heating in winter all warrant calling an engineer rather than attempting DIY fixes.
When you call a Gas Safe engineer, here’s what they’ll do to diagnose and fix your boiler properly.
Fault Code Diagnosis
Modern boilers display alphanumeric fault codes when something’s wrong. Each code points to specific issues—low pressure, sensor faults, ignition problems, circulation issues.
Engineers have manufacturer training and diagnostic equipment to interpret these codes accurately. They don’t just clear the code; they identify why it appeared and fix the root cause.
Accurate diagnosis saves you money. There’s no point replacing a pump if the actual problem is a blocked pipe or faulty sensor. Good engineers test thoroughly before recommending repairs.
Component Repairs and Replacements
Boilers contain numerous components that wear out over time. Pumps fail, sensors drift out of calibration, valves stick, and heat exchangers accumulate limescale or sludge.
Qualified engineers replace these parts safely, ensuring your boiler operates correctly afterwards. They’ll also check related components to prevent further faults appearing shortly after repairs.
Using a Gas Safe registered engineer isn’t just about safety—it’s about getting work that’s guaranteed and compliant with UK regulations. DIY boiler repairs void warranties and can create dangerous situations.
System Cleaning and Flow Checks
Sometimes the fault isn’t in the boiler itself but in your heating system. Sludge build-up restricts flow, affecting boiler performance and triggering error codes.
Engineers can power flush your system, removing magnetite and debris that’s accumulated over years. They’ll also check your pump’s working properly, verify flow rates, and test that water circulates freely throughout your system.
After cleaning, your boiler runs more efficiently, faults reduce, and your heating performs better. Many engineers recommend fitting a magnetic filter to prevent sludge building up again.
If you’re renting, your landlord must fix boiler faults under UK housing law. Adequate heating and hot water are legal requirements for rental properties throughout the year.
Report boiler faults to your landlord in writing as soon as they occur. Heating and hot water failures are emergency repairs—landlords should arrange a Gas Safe engineer within 24 hours.
Tenants shouldn’t attempt fixing boilers themselves except for simple checks like topping up pressure if the landlord’s shown them how. All gas work must be done by qualified engineers.
For landlords: prompt repairs prevent complaints, protect your property, and keep you compliant with housing regulations. Annual gas safety checks are legally required, and regular servicing prevents most common faults before they disrupt tenancies.
You can’t prevent every fault, but these habits significantly reduce breakdowns and extend your boiler’s life.
Book annual boiler servicing. A Gas Safe engineer tests safety controls, checks components, cleans burners, and spots problems early. Annual servicing is required to keep most warranties valid and prevents expensive breakdowns.
Check boiler pressure monthly. Glance at the gauge when heating’s cold. If it drops below 1 bar, top it up before it causes faults. Regular checks help you spot slow leaks early.
Watch for early warning signs. Unusual noises, longer heating times, or radiators not heating as well as they used to all suggest developing problems. Catching these early prevents complete breakdowns.
Don’t ignore fault codes. If your boiler displays an error code, address it properly rather than just resetting repeatedly. Ignoring warnings leads to bigger faults and more expensive repairs.
Keep the area around your boiler clear. Good ventilation prevents overheating. Don’t store items against or on top of your boiler—it needs air circulation to work safely.
These simple actions cost little but save you from cold homes, emergency callouts, and premature boiler replacement.
If your boiler’s displaying error codes, making strange noises, or refusing to provide heating and hot water, book a Gas Safe registered engineer.
Whether you’re a homeowner dealing with an unreliable boiler or a landlord managing rental properties, getting faults diagnosed properly prevents temporary fixes becoming expensive problems.
Look for engineers with experience across different boiler brands who can diagnose accurately, explain problems clearly, and fix issues properly the first time.