Guides & advice
Know your boiler
What our engineers wish every London homeowner knew — about fault codes, losing pressure, radiator faults and the difference between a firm that diagnoses and one that just resets it.
Fault Diagnosis · 3 min read
Boiler Losing Pressure: What It Means and What to Do
A boiler that needs a rare top-up is normal. One that needs topping up every few weeks has water leaving the system somewhere — and that is worth finding, not repeating.
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Fault Diagnosis · 4 min read
No Heating or Hot Water: A Diagnostic Checklist Before You Call
A few safe checks — pressure, thermostat, fault codes — take minutes and either fix the problem or give the engineer a faster starting point.
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Fault Diagnosis · 3 min read
Why Is My Boiler Making a Banging Noise?
A loud banging or knocking noise from your boiler, often called 'kettling', is typically caused by a restriction in water flow, leading to overheating and steam bubbles that collapse violently. The most common culprits are limescale build-up on the heat exchanger or sludge in the system.
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Fault Codes · 3 min read
Worcester Bosch vs Vaillant Fault Codes: What Actually Differs
Worcester Bosch and Vaillant fault codes differ primarily in their format and display method, not the core faults they indicate. Both systems point to similar issues like ignition failure or low pressure, but require different diagnostic approaches.
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Fault Diagnosis · 3 min read
Frozen Condensate Pipe: What To Do Before You Call an Engineer
A frozen condensate pipe is a common cause of boiler lockouts in cold weather. You can try to safely thaw it with warm water, but if the issue persists or you smell gas, you must contact a Gas Safe engineer immediately.
Read guideBoiler Repair · 3 min read
Combi, System or Regular Boiler: Which Do You Have, and Why It Matters
Identifying whether you have a combi, system, or regular boiler is essential for understanding faults and repairs. Each type has different components and requirements, which directly impacts how an engineer diagnoses issues and what parts are needed.
Read guideMaintenance · 3 min read
How Often Should a Boiler Actually Be Serviced?
Your boiler should be serviced once a year by a fully Gas Safe registered engineer. This is crucial for safety, maintaining efficiency, and keeping your manufacturer's warranty valid.
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Fault Diagnosis · 3 min read
What Does a Diverter Valve Do, and Why Does It Fail?
A diverter valve is a key component in combi boilers that switches hot water between your taps and central heating radiators. It commonly fails due to wear, limescale, and system sludge, leading to problems like no heating or hot water.
Read guideFault Diagnosis · 3 min read
Boiler Short-Cycling: Why It Turns On and Off Repeatedly
Boiler short-cycling, where it rapidly turns on and off, is usually a sign of overheating, low water pressure, or a faulty component like a thermostat. It's a problem that needs a professional diagnosis to prevent damage and restore efficient heating.
Read guideBoiler Repair · 3 min read
Is It Worth Repairing an Old Boiler, or Time to Replace It?
Deciding whether to repair an old boiler or replace it involves weighing its age, the cost and frequency of repairs, and its energy efficiency. A new boiler may be a more reliable and cost-effective long-term solution.
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Radiators · 3 min read
Central Heating Sludge: The Signs You Need a Power Flush
Sludge in your central heating system causes cold spots on radiators, strange boiler noises, and poor efficiency. A professional power flush cleans the system, restoring heat and preventing damage.
Read guideFault Diagnosis · 3 min read
Boiler Won't Reset? What That Usually Means
A boiler that won't reset is in a safety lockout, meaning the fault is still present. Common causes include low water pressure, a blocked condensate pipe, or a faulty ignition or sensor.
Read guideMaintenance · 3 min read
Smart Thermostats and Boiler Faults: What to Know Before You Blame the Boiler
A boiler that won't respond often has a simple smart thermostat fault. Checking power, connections, and settings can save you an unnecessary engineer call.
Read guideBoiler Repair · 3 min read
How Long Should a Boiler Actually Last?
A well-maintained modern boiler typically lasts 10-15 years. Its actual lifespan depends heavily on model quality, installation, and annual servicing.
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Gas Safety · 3 min read
Landlord Gas Safety Certificate (CP12): What Tenants and Landlords Need to Know
A Landlord Gas Safety Certificate (CP12) is a legal requirement for any rented property with gas appliances. It confirms an annual safety check by a Gas Safe registered engineer to protect tenants.
Read guideRadiators · 3 min read
Radiator Balancing Explained: Why Some Rooms Never Warm Up
Some rooms stay cold because your heating system's water flow is unbalanced, favouring the nearest radiators. Balancing adjusts the valves to distribute heat evenly to all radiators.
Read guideFault Diagnosis · 3 min read
Why Does My Boiler Keep Losing Pressure After a Repair?
If your boiler continues to lose pressure after a repair, it's likely due to a new leak introduced during the work, a problem with the pressure relief valve, or trapped air in the system. A Gas Safe engineer should investigate to find the root cause.
Read guideBoiler Repair · 3 min read
Emergency vs Routine Boiler Repair: How to Tell the Difference
An emergency requires immediate action for safety or to prevent major damage, like a gas leak or total heating loss in winter. A routine issue, like a single cold radiator, can be scheduled for repair.
Read guideFault Diagnosis · 3 min read
What Is a Boiler PCB, and Why Does It Fail?
A boiler PCB is the main printed circuit board that controls all electronic functions. It fails due to moisture, power surges, component wear, or age, requiring a Gas Safe registered engineer for diagnosis and replacement.
Read guideFault Diagnosis · 4 min read
Why Does My Boiler Make Different Noises? Banging, Gurgling, Whistling Explained
Different boiler noises point to specific faults: banging often means kettling from limescale, gurgling suggests trapped air or condensate issues, and whistling indicates limescale or pump problems.
Read guideRadiators · 4 min read
Why Won't My Radiators Heat Up Evenly? Top Cold, Bottom Cold, One Cold Explained
Uneven heating in radiators is usually due to trapped air, internal sludge, stuck valves, or a system-wide issue like low pressure. Identifying the specific pattern of cold spots points to the underlying cause.
Read guideFault Diagnosis · 3 min read
Why Is My Vaillant Boiler Losing Pressure?
A Vaillant boiler repeatedly losing pressure is most commonly caused by a leak in the heating system or a fault with an internal component like the expansion vessel or pressure relief valve.
Read guideFault Diagnosis · 3 min read
Why Does My Worcester Bosch Boiler Keep Turning Off?
Your Worcester Bosch boiler may be switching off due to low water pressure, a blocked condensate pipe, or internal component faults like a failing pump or diverter valve. A Gas Safe registered engineer is needed to diagnose the specific cause safely.
Read guideFault Diagnosis · 3 min read
Why Is My Ideal Boiler Not Giving Hot Water?
When an Ideal boiler's heating works but hot water is absent or lukewarm, the diverter valve is the most common culprit. An engineer will also check the plate heat exchanger, pump, and boiler controls to pinpoint the exact fault.
Read guideFault Diagnosis · 3 min read
Why Won't My Baxi Boiler Fire Up?
When a Baxi boiler attempts to ignite but fails to light and run, common causes include a frozen or blocked condensate pipe, low system pressure, or a faulty ignition electrode or gas valve. A Gas Safe engineer will systematically check these components to isolate the fault.
Read guideFault Diagnosis · 3 min read
Why Does My Glow-worm Boiler Keep Locking Out?
A Glow-worm boiler that keeps locking out is usually failing a critical safety or operation check, most commonly due to ignition issues, poor water circulation, or incorrect system pressure. A Gas Safe registered engineer diagnoses the specific cause.
Read guideFault Diagnosis · 3 min read
What Is a Pressure Relief Valve, and Why Does It Drip?
A pressure relief valve (PRV) is a boiler safety device that releases water if pressure gets too high. A persistent drip often means the valve is worn or fouled and needs replacing by a Gas Safe engineer.
Read guideFault Diagnosis · 4 min read
What Is an Expansion Vessel, and How Do You Know It's Failed?
A boiler's expansion vessel is a small tank with an air-filled diaphragm that absorbs water as it heats up, preventing dangerous pressure spikes. You know it's failed if your boiler pressure is erratic, you're frequently topping up, or the pressure relief valve is dripping.
Read guideMaintenance · 3 min read
Why Does My Thermostat Not Match the Actual Room Temperature?
A thermostat showing the wrong temperature is often due to poor placement near heat sources or draughts, a faulty internal sensor, or calibration drift. You can test if the boiler works by using its manual override.
Read guideMaintenance · 3 min read
Why Does My Central Heating Programmer Stop Working?
A central heating programmer can stop working due to simple power or battery issues, a schedule being accidentally reset, or internal faults. Checking the basics can often resolve it, but a persistent fault may need professional diagnosis.
Read guideFault Diagnosis · 3 min read
Why Does Hot Water Run Cold, Then Hot Again?
If your combi boiler's hot water runs cold then hot, common causes are limescale in the plate heat exchanger, a sticking diverter valve, or a faulty flow sensor. This is a fluctuation fault, different from a total loss of hot water.
Read guideMaintenance · 3 min read
White Smoke (Pluming) From the Boiler Flue: Is It Normal?
A white plume from a condensing boiler flue in cold weather is normal water vapour, not smoke. It becomes a concern if it persists in mild weather, smells odd, or is accompanied by black soot.
Read guideFault Diagnosis · 3 min read
Why Is There No Hot Water But the Heating Still Works?
This specific fault, where heating works but hot water doesn't, is almost always caused by a problem inside your combi boiler, most commonly a stuck or failed diverter valve that can't switch to hot water mode.
Read guideFault Diagnosis · 3 min read
Why Does My Boiler Lose Pressure More Often in Winter?
Boiler pressure loss is more common in winter because cold weather can reveal small existing leaks, cause condensate pipe blockages that mimic pressure faults, and put more strain on system components due to constant use.
Read guideFault Diagnosis · 5 min read
Why Won't My Boiler Ignite? Pilot Light and Ignition Faults Explained
A boiler that won't ignite is often due to a pilot light that needs relighting, a faulty ignition electrode, a gas supply issue, a faulty gas valve, or a defective flame sensor. Only the pilot light is safe to attempt yourself.
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