Emergency Boiler Repair
Fast Response, All Makes & Models

The most common faults and what they usually mean

No heating and no hot water. If both have gone at once, the fault is usually upstream of the heating and hot water split: low pressure, a failed pump, a circuit board fault, or the boiler locking out on a safety condition.

Hot water but no heating, or the reverse. This pattern points at the diverter valve, the component that decides where heated water goes. Valves seize and their actuators fail. It is a common repair and usually a worthwhile one. See no hot water but heating works.

Low pressure. A combi generally wants around 1 to 1.5 bar when cold. Pressure falling slowly over months is usually air leaving the system. Pressure falling within days means a leak, a failed expansion vessel, or a discharging pressure relief valve. See boiler keeps losing pressure.

Leaking. Where the water comes from matters. A drip at a radiator valve or a compression joint is a plumbing repair. Water from inside the casing, or from the pressure relief pipe outside, means an internal fault or an over-pressurised system, and needs an engineer.

Banging or kettling. Kettling is water boiling and flashing to steam against a scaled or sludged heat exchanger. It means the boiler is running hotter in places than it should, usually because the system needs cleaning. See boiler making a banging noise.

Ignition failure. The boiler tries to fire, clicks, and locks out. Causes range from no gas supply to a dirty flame sensing electrode, a gas valve fault or a blocked flue. All engineer work.

Frozen condensate in winter. Condensing boilers drain acidic condensate through a plastic pipe. If it runs outside and freezes, the boiler cannot drain and shuts down. One of the most common midwinter call-outs, and the permanent fix is insulating, upsizing or rerouting that pipe. See frozen condensate pipe.

What you can safely check yourself

These are the only things we suggest doing without an engineer present.

• Read the pressure gauge. If it is below the manufacturer cold figure, repressurise using the filling loop. Go slowly and stop at the right pressure. If you are doing this more than occasionally, stop and book an engineer, because you have a leak or a failed expansion vessel.
• Check the thermostat and programmer. Flat batteries in a wireless room thermostat cause a surprising number of no-heating calls, as do timers that reset after a power cut and holiday modes left on.
• Check the gas is on. On a prepayment meter, check the credit. Try another gas appliance such as a hob. If nothing gas-fired works, the boiler may not be the problem.
• Bleed your radiators. Cold at the top and warm at the bottom is trapped air. See how to bleed a radiator. Check the system pressure afterwards, because bleeding lets pressure out.

That is the complete list. Do not remove the boiler casing, do not touch gas pipework or components, and do not keep pressing reset. Repeated resetting clears the lockout the boiler used to protect itself without fixing the cause, and on a combustion fault that can mean running an appliance producing carbon monoxide.

When it stops being a DIY job

Anything sealed behind the casing is engineer work. Gas appliance work is restricted by law to Gas Safe registered engineers, and the casing forms part of the sealed combustion circuit. Disturb that seal and fail to reinstate it correctly and combustion products can enter the room.

Book an engineer for a fault code that will not clear, a smell of gas, sooty or yellow staining, a yellow rather than crisp blue flame on an older appliance, water inside the casing, repeated lockouts, a carbon monoxide alarm sounding, or pressure that will not hold.

You are entitled to ask any gas engineer to show their Gas Safe ID card before starting, and to read the back, which lists the specific gas work that individual is qualified to do. Please ask. A genuine engineer expects it.

Boiler fault codes by brand

Plain-English guides to each of these codes are being published shortly. In the meantime, call us with the code and the model and we will tell you what it means.

Most modern boilers tell you what is wrong before an engineer arrives. We have written plain-English explanations of the codes we are called to most often: what each means, whether you can resolve it yourself, and what the repair involves.

Vaillant. Vantage is a Vaillant accredited installer, so these are the boilers we see most.
F22 low water pressure · F28 ignition failure · F29 flame loss · F75 pump or pressure sensor · F27 false flame signal · F20 overheat cut-out · F23 flow and return difference · F83 no temperature rise · F32 fan fault · F62 gas valve shut-off delay · F61 gas valve control fault · F72 flow or return sensor

Ideal. The other range we install regularly.
F1 low water pressure · L2 ignition lockout · F2 flame loss · F3 fan fault

Baxi and Potterton.
E133 ignition failure · E110 overheat · E125 circulation fault · E119 low pressure

Glow-worm, Viessmann and Worcester Bosch.
Glow-worm F28 · Glow-worm F22 · Viessmann F4 · Worcester Bosch codes

We repair and install Worcester Bosch appliances. We are not a Worcester Bosch accredited installer and we will not claim to be.

If your boiler shows a code that is not listed, call us with the code and the model and we will tell you what it means. The full boiler advice section has every guide we have written.

Repair or replace, honestly

We repair far more boilers than we replace, and a well maintained boiler with one fault is usually worth repairing. Replacement makes better sense when several of these are true at once.

Parts availability has become genuinely difficult, which for most manufacturers starts to bite roughly a decade after a model is discontinued. The boiler has failed repeatedly in a short period, which usually means the underlying cause was never dealt with. The heat exchanger has gone, the single most expensive component. The appliance is non-condensing, so a modern replacement would use meaningfully less gas for the same heat. Or it is badly sized for the property.

Replacement is not automatically right just because a boiler is over ten years old, and we will not tell you it is. Equally, if we think you are about to spend serious money on an appliance that will fail again within the year, we will say so. Where a system has repeatedly destroyed its own components, the honest answer is often that the system water needs cleaning, not that the boiler needs replacing. See how long does a boiler last.

Frequently asked questions

Can I repair my own boiler?

Only in the narrow sense above. You can repressurise, bleed radiators, check the thermostat and check your gas supply. Anything needing the casing off, or involving gas components, is restricted by law to Gas Safe registered engineers and is dangerous to attempt otherwise.

My boiler keeps losing pressure. What is wrong?

Something is letting water out: usually a small leak on pipework or a radiator valve, a failed expansion vessel, or a pressure relief valve passing water to the outside discharge pipe. Repeated topping up hides the fault and keeps introducing fresh oxygenated water, which accelerates corrosion.

Why does it keep locking out?

A lockout is a deliberate safety response to something the boiler detected, usually failed ignition, flame loss, overheat or a flue problem. Resetting clears the lockout, not the cause. If it happens more than once, stop resetting and book an engineer.

Do you repair boilers you did not install?

Yes, all the major domestic brands. Tell us the make, model and fault code when you call and we can usually arrive with the right part.

Should I ask to see a Gas Safe card?

Yes, every time, with any company. The card carries the engineer photograph, registration and expiry date, and the reverse lists the appliance types they are qualified to work on.

Where we cover: Our engineers cover boiler repair across Hertfordshire and the surrounding counties, including Stevenage, Hitchin, Letchworth, Welwyn Garden City, Hertford, Ware, St Albans, Harpenden.