Gas boiler faults

Boiler Repair Specialists, London

Same day repair 24/7

Answered 24 hours a day by somebody who knows boilers.

What is the problem?

Gas Safe registered engineers
An engineer to visit booked around you
We work on cylinders as well as combis
Parts guaranteed for a year

No heating or hot water right now? Call 0203 868 6134. We will tell you the earliest realistic slot rather than the one you want to hear.

Prefer we call you? Request a call back

Two details to start. Tell us the make and what has stopped and we can usually work out the part before we come.

We cover the whole of London

Tell us the address and you will have an honest answer about how soon somebody can be there, before the call is a minute old.

Book an engineer

Google Reviews

"Engineer excellent and very time efficient."
Fiona G.
"Efficient and amiable service all round. Even managed to save me money by fixing a thermostat that we thought was broken."
Graziano B.
"Steve was very helpful and responsive"
Richard E.

What happens when you call

Three steps, and you will know where you stand before an engineer is booked.

Tell us what has stopped and what the boiler is showingHeating, hot water or both, and any code or light on the display. If you can see the make on the front, that is enough. We work out the rest.
The likely part, and a realistic slotWe tell you the likely part and a realistic slot. If we cannot reach you today we say so on the phone, rather than after you have waited in.
The engineer attends and runs a full diagnosticYou get a written breakdown before any repair begins: what has failed, what the parts and labour come to, whether the part is on the van or has to be ordered, and roughly how long the work will take. Nothing goes ahead until you have seen that and agreed to it. Parts are guaranteed for a year.

If we cannot get to you tonight, we will say so on the phone. A firm that promises an hour to everybody who rings is making the same promise to the person before you. We would rather give you an honest answer while you still have time to try someone else.

How we diagnose a fault

Six tools. Each one gives a number, so anybody can check our answer.

Flue gas analyser

Tests what is coming out of the flue. It tells us the boiler is burning safely. If the reading is wrong we stop and look, rather than leave it running.

Manometer

Measures the gas pressure at the boiler. It tells us whether the boiler is getting enough gas, or whether the gas supply is the problem.

Gas meter and a stopwatch

We time the meter to see how much gas the boiler is really using. It tells us whether it is working as hard as it should be.

Multimeter

Tests each part for electrical faults, one at a time. It tells us which part has actually failed, not which one is easiest to change.

Pressure gauge, hot and cold

We watch the pressure as the boiler heats up. That tells a leak apart from a failed expansion vessel. They look the same otherwise.

A magnet and a water sample

Shows what is in the water going through the boiler. That tells us whether the problem is the boiler or the pipes and radiators.

Did you know If anyone quotes you for a part, ask them what reading they got. If they tested, they will tell you straight away. If they guessed, they cannot answer.

Symptom & Solutions

What each problem usually turns out to be.

What you are seeing	On a combi	With a hot water cylinder
Heating gone, hot water fine	Diverter valve, or its cartridge alone	A motorised valve or the room thermostat, not the boiler
Hot water gone, heating fine	Diverter valve stuck the other way, or the flow sensor	Cylinder thermostat, immersion, or a valve that has stopped opening
Hot water lukewarm or swinging	Scaled plate heat exchanger, the commonest London fault of all	A scaled coil inside the cylinder
Neither working	Ignition, gas valve, or a lockout the boiler is holding for a reason
Losing pressure	Once a year is normal. Every few weeks is a leak. Every few days is the expansion vessel
Banging or kettling	Scale or debris on the main heat exchanger. Worth acting on, because that is the expensive part
Radiators cold at the bottom	Not the boiler. Magnetite, and a power flush rather than a part
Drops out only under load	Almost always the gas supply rather than the appliance

Worth saying when you ring: whether you have a hot water tank in an airing cupboard. The same problem means a different part depending on the answer.

Do you need a second opinion on a quote?

Tell us what you were told. If it sounds right we will say so and help put your mind at rest.

Call 0203 868 6134

An unhealthy boiler can be costly

We provide solutions for a healthy system, helping you reduce unnecessary costs.

It runs fine on a mild day. Then it gets cold, or someone runs a bath with the heating on, and it cuts out. You reset it and it works again. Most people are told it is a faulty fan, sensor or circuit board. Usually it is none of those. The boiler simply cannot get enough gas when it is working hard. We check it by measuring the gas pressure at the boiler while it runs flat out.

If the pressure drops too far, the gas pipe feeding the boiler is too small or too long. No new part will ever fix that. It is how people end up paying for a fan, a sensor and a circuit board in one winter, and still have the same problem in February.

When it is not the boiler at all

About one call in three turns out not to be the boiler. These four cover most of them.

The controlsFlat batteries in a wireless thermostat, or a timer that lost its settings in a power cut. Both make a boiler look completely dead. Both are free to check.
The stored hot water sideIf you have a hot water tank, the boiler is often fine and the fault is in the tank or its valves. That is unvented cylinder repair, and it needs a qualification most firms do not have.
The system waterCold radiators, a noisy pump and parts that keep failing usually mean sludge in the system. New parts will just fail again.
The gas supply or the meterIncluding a prepayment meter that has quietly run out.

When a repair is the wrong answer

Which part has failed matters far more than how old the boiler is.

Under eight years

Almost always worth repairing. Check the guarantee first. Many boilers now come with ten or twelve years cover, as long as it has been serviced every year, and most people forget they have it.

Eight to fourteen years

It depends on the part. A sensor, a pump or an expansion vessel is worth doing. A main heat exchanger or a gas valve is a big share of a new boiler, so that is a closer call.

Fifteen years and older

Here it comes down to whether the part is still made. If it is not, the repair is not slow or dear, it is impossible. We check that before you pay us anything.

Whichever it is, you are told before you pay anything. Our Powermax 155x case study shows a discontinued appliance repaired rather than replaced, photographed step by step.

No gas supply? We repair & fit electric boilers

An electric boiler has nothing burning in it, so different things go wrong: the heating element, the switch gear or the wiring. Fewer faults, but they are electrical ones. Most gas engineers will not touch one. That is why people ring three firms and get three noes. We do repair them, and it is a different page: electric boiler repair in London.

We cover the whole of London

These are where we work most, not a boundary. An engineer attends anywhere in north London and south London. Tell us where you are and we will say plainly when we can get to you.

Districts including Clapham and Battersea, Ealing and Northfields and Crystal Palace each have their own page. The full list is on areas we cover.

Safety

If you smell gas: do not touch any switches. Open the windows, leave the property, then call the National Gas Emergency Service on 0800 111 999. That line is free and open 24 hours. Call them before you call us. If a carbon monoxide alarm is sounding: get everyone out immediately, then call 999 if anyone feels unwell. Do not go back in until the property has been ventilated and checked. If the boiler locks out repeatedly: try one reset. If it locks out again straight away, stop. Repeated resets hide a fault that is still there, and on a gas appliance that is not a risk worth taking. Under the Gas Safety (Installation and Use) Regulations 1998, only a Gas Safe registered engineer may work on gas appliances. Never open the boiler casing yourself.

Common questions

How do I know an engineer diagnosed the fault rather than guessed?

Ask what reading the diagnosis came from. Every genuine diagnosis produces a number: a combustion ratio off the analyser, a gas pressure off the manometer, a resistance off the multimeter. Somebody who measured will tell you the figure without hesitating, because it is written on the instrument. Somebody who swapped parts until one worked has no figure to give.

My boiler works until it works hard, then cuts out. What is that?

Usually the gas supply rather than the appliance. The boiler runs happily at low fire and fails at high fire, which looks identical to an intermittent fan, sensor or board. The test is working pressure measured at the appliance while it runs at full rate, with no more than about a millibar lost between the meter and the boiler. Lose more and the pipework is too small or too long, which no part fitted to the boiler will ever fix.

The heating works but there is no hot water. Do I need a new boiler?

Almost certainly not. On a combi that pattern points at the diverter valve, often just its cartridge, or the flow sensor. On a system with stored hot water the boiler is usually working perfectly and the fault is the cylinder thermostat, the immersion or a motorised valve. Tell us which you have when you ring and it halves the diagnosis before anybody sets off.

Can I reset the boiler myself?

Once, yes. If it locks out again straight away, stop and leave it off. The boiler is refusing to run for a reason and repeated resets hide a fault that is still live. Where the heating has gone completely and it is the middle of the night, that is emergency boiler repair rather than something to keep restarting until morning.

Why does my hot water go lukewarm and then hot again?

On a combi that is a scaled plate heat exchanger, and in London it is the commonest hot water fault there is. The heating side carries on perfectly, which is what persuades people the whole boiler is dying when the appliance is in good order. London water runs at roughly 277 milligrams of calcium carbonate per litre, so it happens faster here than the manufacturer assumed.

Do you charge to diagnose a fault?

The rate is agreed with you on the phone before anybody sets off, and you get a written breakdown of the fault, the part and the labour before any repair begins. Nothing proceeds until you have seen it. If the honest answer is that the boiler is not worth repairing, we say so and there is nothing to pay for being told.

Google Reviews

"Very polite and respectable engineer...had two other heating company that struggle to find the issue with my boiler but ASAP repaired it on the same day thanks absolute life saver"
JA Morris
"Very happy with this company very and professionally service. Fixed my leaking TRV and after draining my system and the refilled and vented the air . Thank you I have heating now"
Jamie K.
"These guys provide an excellent service. A pleasure to deal with and professional"
Day Walker

Book a boiler engineer

Tell us what has stopped and roughly where you are. That is enough to work out the likely part, give you the rate, and book somebody in, all on one call.

Call 0203 868 6134 Book an engineer online

Gas Safe registered. Unvented cylinder qualified. Parts guaranteed for a year. Covering London, north and south of the river, 24 hours a day.