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Breakdowns And Boiler Repair London

What causes a boiler to breakdown?

Boilers often break down during the winter months when you need and value them the most. This isn’t just because they are working overtime. Long periods of inactivity in the summer months can cause parts to seize and the cold, winter weather can freeze discharge pipework. An annual service can help prevent a lot of potential boiler breakdowns, so it is always a good idea to have this carried out towards the end of the summer months. Please see our list below of common boiler faults.

How is a boiler fault diagnosed?

Across North London our trained engineers can identify the source of a boiler fault through experience or by carrying tests on certain components with an electrical multi-meter. You should never attempt a boiler repair on your own as only Gas Safe registered engineers are permitted to remove the boiler casing. ASP Plumbing and Heating Services are Gas Safe registered and have the experience and equipment to diagnose and repair boiler faults quickly and efficiently.

Boiler Repair London Specialists

Boiler repairs in London conjures up images of extortionate repair costs and days without heating and hot water and is undoubtedly what every homeowner dreads. At ASP Plumbing & Heating Services we aim to carry out a quick diagnosis and provide the customer with a fair, fixed price based on our hourly rate.

We have over 10 years of experience in diagnosing faults and boiler repair in homes around North London. We are Gas Safe Registered, meaning we can work on boilers safely.

We specialise in repairing some of the biggest boiler names on the market, including Vaillant, Worcester, Baxi, Potterton, Glow Worm and Ideal.

How much does a boiler repair cost?

Boiler repair costs can vary greatly depending on the parts required and the length of the job. Please see our Prices section for more details.

ASP Plumbing and Heating Services specialise in repairing some of the biggest boiler names on the market, including Vaillant, Worcester, Baxi, Potterton, Glow Worm and Ideal. If you have query regarding a boiler breakdown please call us on 020 3858 0277 or get in touch using our contact form.

Boiler Repair London Common Faults

Below are some of the typical faults we come across when we are delivering boiler repairs across London. If you have one or more of these issues with your boiler get in touch we can help.

Loss Of Pressure In Boiler

Combination and system boilers must be at the correct operating pressure (between 1 -2 bar) for your system to work properly. Typically, if your system pressure falls below 1 bar your boiler will implement a safety lockout feature to prevent it from firing until re-pressurised. This is to protect the boiler components from damage caused by operating under the incorrect operating pressure.

Re-pressurising your boiler is straightforward enough and can usually be carried out by the user with reference to the manufacturer’s instructions, but frequent pressure loss usually means there is a fault within your heating system.

Your boiler could be losing pressure for several reasons. Pressure loss is most commonly caused by a leak in the heating system, typically from a radiator valve or boiler component. Another common cause is a faulty expansion vessel and pressure relief valve. The expansion vessel, typically located inside the boiler, contains air as well as water from the heating system. When the water in the heating system heats up and expands, the air pocket compresses to take up the expansion. If the air pocket depletes or the diaphragm in the vessel becomes perforated, the pressure in your heating system will fluctuate extensively, often triggering the pressure relief valve. Typically, both parts are replaced at the same time.

PCB and Ignition failure

The PCB (Printed Circuit Board) is essentially the brain of your boiler, telling it when to turn on the pump, when to ignite and how much gas to use. If the PCB fails, the boiler will usually start behaving peculiarly or displaying several fault codes relating to ignition failure. Unfortunately, PCB failures are quite common, but are usually straightforward to diagnose.

Another common cause of ignition failure is faulty spark generators and electrodes. These parts are responsible for creating the spark required to fire up the boiler. If they fail, the boiler will be unable to ignite and will display a fault code. Gas valves, which regulate the gas supply to your boiler, can also fail but this occurrence is less common.


Boilers will typically lockout if they overheat, accompanied by high display temperatures and strange banging noises. The most common causes of boilers overheating are pump failure, sludge build up, air in the system, or faulty thermostats.

If you suspect your boiler is overheating, it may be a good idea to try to bleed your radiators to check for air in the system. If this is unsuccessful, it is unwise to attempt any further repairs on your own and you should contact ASP Plumbing and Heating Services straight away.

Boiler Diverter Valves

Combination boilers feature a diverter valve and motor which sends water to either your hot taps or radiators on demand. Sometimes, either the valve pin or motor can stick, preventing the valve from opening or closing properly. This is especially true after the summer months, when your heating has been inactive for a considerable time.

Radiators heating up when a hot tap is switched on, lukewarm hot water, or no heat to your radiators are the tell-tale signs of a faulty diverter valve.

Frozen Or Blocked Condensate Pipes

Condensing boilers reclaim heat from flue gasses in the form of condensation. Once the condensed water has cooled, it is sent to the condensate trap and down a connected drainpipe.

If your boiler condensate pipe terminates at an external drain, then it may be susceptible to freezing. Frozen condensate pipes will prevent the wastewater from draining away and stop your boiler from igniting. A blocked condensate trap can also cause the same problem. If a boiler isn’t regularly serviced, then sediment can build up in the condensate trap and prevent the water from draining away. Cleaning of the condensate trap is included during the annual service.

Boiler Plate Heat Exchangers

Plate heat exchangers are parts in combination boilers that are responsible for indirectly heating the water for your taps. If these become blocked with sludge or limescale, your boiler will tend to overheat in hot water mode. If your water is initially extremely hot before running lukewarm, it could be a faulty plate heat exchanger.

Boiler Pump Failure

Pumps are responsible for circulating the heat around your boiler and to your radiators. Pumps can seize or burn out over time, resulting in boiler overheating, poor circulation to radiators, or lockout faults. Pump failure is an easy fault to diagnose and repair.

Breakdowns aren’t always caused by faulty components in the boilers themselves. Sometimes the problem can lie with the pipework, external circulating pump, or motorised diverter valves. Click here for more on heating system repairs.

The build-up of sludge and debris in heating system pipework is a common contributing factor when it comes to the failing of pumps and sub-par heat output from radiators. Having your heating system flushed or installing a magnetic system filter is great way to rid your heating system of sludge and debris, enabling it to run far more efficiently and circulate the heat around your radiators more quickly.

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If your boiler is giving problems or has stopped working we can help. Use our contact form or call now 020 3858 0277.
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