Boiler Repair Guide

By Rachel
Last updated 23rd November 2021 - Reading time: 23 mins

If you need to have your boiler repaired but are unsure what is involved, this guide will give you some insight and some general costs for boiler repair. We will look at the different types of repair that may be needed, how long they may take and some average prices.

The requirement for a qualified person to carry out the repair will be explained and what to look for when hiring.

Boiler repair

The decision about whether to repair or replace your boiler if something goes wrong will be considered, and in what circumstances replacement is preferred to repair.

We will look at the advantages and disadvantages of boiler repairs. Depending on the type of boiler you have installed, you may encounter different issues, and so the method of fixing will vary.

What is a Boiler Repair?

At some point, your boiler may develop a problem that needs to be fixed. This may be an emergency boiler repair or something that comes up during an annual service. Either way, you will need to have a qualified heating engineer or plumber fix it or advise whether the boiler should be removed and replaced.

A boiler repair is something that needs to be done for the boiler to carry on working effectively and efficiently. This may mean that parts need to be replaced or a component of the boiler needs to be fixed.

It is important if there is an issue with your boiler that you have it repaired as soon as possible. A boiler that isn't functioning properly will not only cost you money but may also be dangerous. This is why it is important to have a qualified heating engineer or plumber carry out the repair.

Fixing a boiler

If a boiler is not working effectively, it could be releasing harmful carbon monoxide into your home. This invisible gas is a real danger to your health and, if left unchecked, can be fatal.

A boiler that is not working correctly will also cost you money as you will be paying for the fuel but not getting the benefit of a fully efficient boiler. A drop in efficiency to 60%-70% means that for every £100 you spend on fuel, £30-£40 of that money is being wasted.

While boiler repair costs may worry some people, the price you pay will be worth it if the boiler is repaired and works effectively. The alternative is that the issue with the boiler worsens and causes even bigger and more expensive problems. If left for long enough, some issues may mean that the boiler will need to be replaced.

Types of Boiler Repairs

A problem with your boiler may arise in different situations, and the type of issue you may encounter can often depend on the type of boiler you have.

Emergency Boiler Repairs

If you have a gas boiler and smell gas in your home, you should act immediately. If you know how to turn off your house's gas supply, you should do this and get everybody outside. Open all windows and doors to ventilate the area and don't allow anyone to smoke or operate mobile phones in the house.

Once outside, you can call the National Gas Emergency Service Provider (ESP) and advised them of the situation.

A heating engineer or Gas Safe plumber should be sought to deal with why there is a gas leak in your home, and if it is coming from the boiler, they will need to diagnose the fault.

Emergency boiler repair

For households with elderly people or children, if your boiler stops working and you have no heating or hot water, this is considered an emergency repair.

If your home burns any kind of fossil fuel such as natural gas, oil or wood, you should have a carbon monoxide detector in case of a leak. If your carbon monoxide detector goes off, you should switch off any fossil fuel-burning appliances and call a professional heating engineer.

If there is a substantial water leak from your boiler, then you will need to call an emergency plumber or heating engineer as they are trained in how to repair a boiler. Do not try to repair a boiler yourself, as it is definitely not a DIY job that can be done safely.

Cost of Emergency Boiler Repairs

How much you pay for an emergency boiler repair will depend on the time of day, the nature of the problem and where you live in the UK. The average cost may be around £100-£500.

Gas Boiler Repairs

The majority of homes in the UK use gas boilers for their heating and hot water as most properties are connected to the gas grid, and it is one of the cheapest forms of fuel available in the UK.

As with emergency boiler repairs, a gas boiler repair can involve a gas leak. This will require a call to the National Gas Emergency Service Provider or an emergency Gas Safe heating engineer.

Carbon Monoxide

A carbon monoxide leak is also a serious gas boiler repair issue and must be dealt with immediately. It is vital that you have a carbon monoxide detector fitted in your home if you use any fossil fuel appliances.

If the detector sounds an alarm, you should contact a qualified heating engineer and have them attend as soon as possible to find the source of the problem.

Gas boiler parts

While you are waiting, you should make sure the property is well ventilated, and vulnerable people such as children or the elderly do not remain in the house.

Potential Problems

There are many parts of a gas boiler that could potentially fail and require a repair. If there is a leak, it may be because a pressure valve or pump seal is no longer working properly. This faulty part can be removed and a new one installed to rectify the problem.

Low pressure in the boiler can sometimes be a problem. If you have called a plumber or heating engineer and this is found to be the fault, it is often a case of simply topping up the boiler with water. So, ask them to show you how to do this so you can carry out a DIY fix if the problem recurs.

A frozen condensate pipe is a typical problem in very cold weather. The condensate pipe runs from the gas boiler to the outside drain, and in winter, this can freeze, causing the condensation to back up and shut the boiler down.

Cost of Gas Boiler Repairs

The average cost of a gas boiler repair will depend on the extent of the problem and where you live. Boiler repair prices will be much higher in London than in other parts of the country, sometimes double the cost.

For a new pump or fan, you can expect to pay around £100-£300, but if you need something like a heat exchanger, it can cost between £300-£500.

Oil Boiler Repairs

Oil boilers can come with their own issues as they require a storage tank on-site rather than being fed directly from the mains like gas.

For this reason, the maintenance and servicing of oil boilers involves checking the oil storage tank as well as the boiler. Similarly, the storage tank can develop problems and need repairs too.

Potential Problems

Contaminants getting into the storage tank can create major problems and cause the boiler to shut down. These contaminants could be water, ice, dirt or even air which can block the flow of the oil to the boiler.

As oil is quite a dirty fuel, the parts of an oil boiler can get clogged and become blocked over time. The maintenance and servicing of an oil boiler involves a lot more physical cleaning of parts than for a gas boiler which is a cleaner fuel.

Oil boiler

Similarly, soot deposits can accumulate on the photocells, which detect if the boiler is lit. This accumulation can cause the boiler to shut down or constantly switch on and off, which is inefficient. Cleaning the photocells will normally fix this problem.

The electrode, which is part of the ignition system for an oil-fired boiler, can also get dirty and clogged up, causing it to fail. It can also get worn over time and not work effectively. Depending on which of these issues causes a problem, the solution will be cleaning or replacing the electrode.

Cost of Oil Boiler Repairs

The cost of repairing a boiler fuelled by oil will depend on the existing problem, but the average cost can be between £75 and £150. The repair may be in the boiler itself or could be an issue in the oil storage tank. Costs will vary according to the extent of the problem and your location in the UK.

What Are the Pros and Cons of Repairing a Boiler?

Deciding on the benefits and downsides of repairing a boiler will rest on various factors, and you may want to consider them all before calling a heating engineer.


Hot Water & Heating

Perhaps the first and foremost advantage of repairing a boiler will be restoring your heating and hot water. The loss of both can be serious, especially in the winter or if there are children or elderly people in the house.


Repairing your boiler will also maintain its efficiency. If there is an issue affecting how well the boiler operates, it will not work at full capacity and is inefficient.

Saving Money

In addition, an inefficient boiler will be costing you money if the amount of fuel you are using is not being effectively converted by the boiler. Most boilers these days should be operating at above 90% compared to older boilers which sometimes only reached 70%-80%.

Boiler repairs

Expand Lifespan

Prompt repairs to your boiler will expand its lifespan. This means that your investment will last longer, and there will be a reduced chance of a major failure or breakdown in the future.


By repairing your boiler, you will increase its reliability and ensure that it is working as it should be for as long as possible.



Unlike many things in your home, a boiler cannot be repaired as a DIY job, and it takes a qualified, experienced professional to diagnose a problem and carry out a repair, which is never cheap. Despite the cost of hiring a heating engineer, it is inadvisable and dangerous to try and repair a boiler yourself.


Deciding whether or not to repair a boiler or simply replace it will often depend on its age. If it is more than ten years old, it may be more cost-effective to replace it.

As a boiler ages, not only does it become more prone to problems, but parts will become harder to source as newer models come on the market.

How Much Do Boiler Repairs Cost?

The cost of repairing a boiler will largely depend on the nature of the problem, the type of boiler and the area that you live in.

Fixed Price Boiler Repair

Some companies offer a fixed price boiler repair. This means that you pay a set price for the repair regardless of how much the repair would be. Any parts that are fitted are charged as extra. This is just one way you can budget for boiler repair costs and is useful when the warranty on the boiler has expired.

Care & Maintenance Plan

You can also buy a care plan which means you pay a fixed monthly fee, and the cost of repairing a boiler will be covered. While this does mean you have to lay out money in advance of any potential repair, it can be useful if you have an unexpected problem with your boiler.

Most of these plans offer a 'no fix, no fee' policy, meaning that if the issue cannot be resolved and the boiler is not repairable, any money paid up till that point will be refunded. Monthly payments can help with budgeting too.

Type of Boiler

Some boiler repair prices will be higher than others. Gas boilers are typically cheaper to fix than an oil boiler or an LPG boiler, as these are much less common. The average gas boiler repair cost for labour is about £50-£65, while for an oil-fired boiler, this may be £60-£85.

Additional Jobs

If you take good care of your boiler, including an annual boiler service, then you may avoid any unexpected repairs and associated costs that you haven't budgeted for. If your boiler cannot be repaired or it is uneconomical to do so, you may need to fit a new boiler.

Installing a new combi boiler can cost around £2,500, but how much you pay will depend on where you live and the specific boiler you choose.

Some issues can be resolved by power flushing your central heating system. Over time sludge builds up in the pipework and can cause problems. Having it removed can have a positive impact on the functioning of the boiler and radiators.

Boiler pipe repairs

Moving a boiler to a new location can also cause debris to be dislodged from the system and travel to the boiler and cause it to stop working properly. The cost of a power flush is around £400.

How to Repair a Boiler

The process of repairing a boiler will depend on the problem, so most jobs will start by trying to diagnose the issue.

Repair Process

There are several common faults that boilers may experience, and the remedy will depend on which of these is affecting your boiler.

Loss of Hot Water & Heating

This problem can be spotted quite early as it is an obvious fault when there is no hot water coming from your taps or shower, and your house is cold. This is unlikely to be caused by a single issue and may be due to the age of your boiler and the wear and tear of parts.

Other possible reasons are low boiler pressure which can be fixed by topping up the water through the feed loop at the base of the boiler. In freezing weather, the condensate pipe may have frozen, which will cause the boiler to shut down. This can be thawed out by pouring warm water over the pipe.

Boiler Leak

A leak from your boiler may not be immediately apparent if it is sited in the garage or a cupboard, so the first sign may be a loss of hot water or heating. The cause of leaks is likely to be an internal component's failure, which will need to be repaired by a qualified and experienced heating engineer or Gas Safe plumber.

Noisy Boiler

An efficient boiler that is working properly should operate relatively quietly, so if there are noises such as banging, whistling, or buzzing, it is highly likely that there is a fault with the boiler. Whistling noises are known as 'kettling' as it sounds similar to a kettle boiling. This can be caused by a build-up of sludge or limescale and needs to be dealt with by a heating engineer who will flush the system.

Banging noises can also be a result of debris in the system, loose pipework or a failure of the pump, which pushes water from the boiler around the central heating system. You should get a plumber or heating engineer to diagnose what the problem is and fix it.

Gurgling noises can indicate that there is air in the system, which can be dealt with by bleeding the radiators. This can be done as a DIY job; all you need is a radiator key to open the valve and release the air. Don't forget to lay a cloth or old towel on the floor beneath the radiator to stop dirty water from staining your flooring.

DIY Repairs

While the majority of repairs must be left to a qualified heating engineer or plumber, some problems can be fixed with simple DIY knowledge.

If your boiler drops below the recommended pressure, usually 1.5 bar, you can top up the water in the boiler through the filler loop below the main casing. The boiler should be switched off before you re-pressurise and turned back on when you have reached the indicated optimum pressure.

When radiators fail to get hot, it may not be a problem with the boiler but could be air trapped in the system. You can remedy this by using a radiator key to turn the valve at the top of the radiator. As air is released, you will hear hissing, once this stops and water starts dripping from the valve, tighten it again. The radiator should now get hot throughout.

Boiler digital display

Make sure you lay an old towel or cloth underneath the radiator before you begin to protect your flooring as radiator water is black and will stain.

Some boilers can be reset with a reset button, and if your boiler stops working, you could try this, but you should refer to the manufacturer's instructions in the first instance.

A frozen condensate pipe may stop your boiler from working in winter, and this can often be rectified by pouring warm water over the pipe to thaw it out.

Dangers of DIY Boiler Repairs

Occasionally these DIY repairs will mean that you do not need to call a plumber or heating engineer, and you may save yourself some money. However, if these repairs do not work, you should call a qualified and experienced professional to determine the problem with your boiler.

Under no circumstances should an unqualified person carry out repairs on a boiler of any type, as this is illegal and very dangerous. Even if someone thinks they know how to repair a boiler unless they are qualified to do so, they should not be allowed to attempt it.

How Long Does It Take to Repair a Boiler?

The length of time to fix a problem with a boiler will depend on the problem and how much of the overall heating and hot water system it is affecting.

Small Repairs

Some of the less serious repairs to a boiler will take no more than an hour or two to sort out, sometimes less. A boiler that is low on pressure can be topped up with water from the feeding loop in a matter of minutes. Regular checks every few hours after topping up will let you know if the problem has been rectified or if there is a bigger problem, such as a leak.

A frozen condensate pipe will make the boiler shut down, but by pouring warm water on the pipe, this can be solved within an hour or two.

If your radiators are only getting partially warm, bleeding them will take less than an hour, or if some are getting hot and not others, they could need balancing. This should be done by a plumber or heating engineer, but you could do it yourself next time if you are shown how to do this. Balancing radiators may take a few hours, depending on how many are in the property.

Major Repairs

Problems that require physical work on the boiler or other parts of the heating system should always be left to a professional and never attempted as a DIY task. Even if you think you know how to repair a boiler, you should never do so and leave it to a qualified plumber or heating engineer.

If you have hot water but no heating, the problem may be due to a broken diverter valve or a faulty diaphragm. Finding the cause of the problem may take an hour or so, and a repair may take 2-4 hours, depending on the make and model of the boiler. Replacing a pump or heat exchanger in a faulty boiler is a big job and will probably take half a day.

Boiler components

Problems with the thermostat may be as simple as replacing the batteries in the thermostat unit or ensuring it is connected to the Wi-Fi if it is a smart thermostat. These jobs will only take a few minutes.

A power flush of the system is a complicated process and depending on the size of the property and the condition of the system, it can take between 6-8 hours to complete.

Building Regulations or Planning Permission Approval for Boiler Repairs

If a hot water or heating system needs to be repaired in an emergency, there is no need to apply for advance approval. Still, the repairs must comply with Building Regulations, and approval should be sought afterwards.

In situations where a heating system has been altered or replaced, the last person to work on it is responsible for its safe running and should issue a certificate to state that all checks have been carried out.

Fixing a boiler with a screwdriver

Work to fit a new boiler needs Building Regulations approval, and this is typically done by an installer who can self-certify their work. The installation must follow the guidelines in Approved Document J of the Building Regulations for safety and energy efficiency compliance. The cost of meeting Building Regulations should be included in the fee that you pay to the installer.

Boiler repairs do not typically require Planning Permission, although if a new flue needs to be fitted to a listed building or property in a conservation or other designated area, it is advisable to check with your local authority first.

Information on Building Regulations and Planning Permission for boiler repairs can be found on the Planning Portal website or by contacting your local authority.

How to Maintain a Boiler

With boiler repair prices being quite expensive, it is in your best interest to take good care of your investment and have a regular maintenance schedule for your boiler and heating system.


One of the most important ways to maintain your boiler is to have an annual boiler service. For most boilers, this will also be a condition of the manufacturer's warranty and ensuring that the boiler is checked yearly should reduce the chance of faults developing and breakdowns.

Follow Manufacturers Recommendations

As well as an annual service, all recommendations by the manufacturer of your boiler should be followed to make sure it works to optimum effectiveness and efficiency. This can include where the boiler is sited to ensure good ventilation and good access to the flue.

Check Pressure

Your boiler pressure should typically be between 1 and 2 bar. This is normally indicated on the boiler pressure gauge. If the pressure is too low, the boiler will not be able to pump the hot water around the system, which means the heating will not work.

Tradesman checking a boiler

It can be dangerous if it is too high, although there is a safety feature called a pressure relief valve on all modern boilers that discharges water if the pressure level rises too much.

Bleed and Balance the Radiators

Bleeding the radiators involves releasing any trapped air in the system and ensuring that they heat effectively. Balancing the radiators means adjusting the valves so that all the radiators heat up simultaneously, ensuring even heat distribution throughout the house.

Visual Check

Every couple of months, it is good to carry out a visual check of your boiler to check for leaks or other visible damage. It is also good practice to listen to the boiler when it is working well so that any unusual noises will alert you to a possible problem. Checking the flue regularly is a good idea too.

Questions to Ask When Hiring a Heating Engineer

When searching for a heating engineer, you need to consider certain things and questions that you should ask before hiring.

  • What qualifications does the engineer have, and can they provide proof of this?
  • How much experience do they have in the particular boiler that you need repairing?
  • Depending on the type of boiler, are thy Gas Safe or OFTEC registered?
  • Do they offer a guarantee for work carried out, and if so, how long for?
  • Are they adequately insured, and can they provide evidence of this?


Why will my boiler not heat up?

If your boiler fails to heat your water and supply the central heating, you will probably need to call a plumber or heating engineer to diagnose the problem.

It could be the boiler pressure is too low or too high, broken internal components, a frozen condensate pipe or a faulty pilot light. Only a qualified and experienced plumber or heating engineer will be able to rectify the problem.

What does it mean when a boiler makes loud noises?

A boiler in good working order normally operates relatively quietly, so if unusual noises are coming from it, there is a problem. These noises may be banging, whistling, or gurgling and can be caused by various issues such as air in the system, limescale or sludge build-up or a faulty internal component.

Can I adjust the pressure in my boiler?

Most boilers operate effectively at between 1 and 2 bar, so if your boiler falls below 1 bar, you can top it up using the feeding loop under the main body of the boiler. This is fitted with two taps which you open to allow water to flow into the boiler.

When the desired pressure has been reached, the taps can be closed. The boiler should be switched off when you do this and switched back on only when the correct pressure has been reached. There is a safety feature on all modern boilers that safely vents excess hot water if the boiler pressure gets too high. This particular problem is best dealt with by a qualified heating engineer or plumber.

Do I need a specialist to fix my boiler?

Boilers are complex appliances, and only properly trained, and qualified tradespeople who know what they are doing should be working on them. A gas boiler should only be repaired by a Gas Safe registered tradesperson, and an oil-fired boiler should be repaired by an OFTEC (Oil Firing Technical Association) registered tradesperson.

While they may be similar in many regards, a Gas Safe registered engineer should not work on an oil boiler, and an OFTEC engineer should not work on a gas boiler. Each has their own speciality and expertise, and this should be adhered to.

Should I repair or replace my boiler?

At some point, you may want to consider if it is economical to repair your boiler. In most cases, if the boiler is around ten years old, then it may be more cost-effective to consider a replacement. Not only will your boiler be more prone to wear and tear as it gets older, but it will also become more difficult to get spare parts and components for it.

Energy efficiency guidelines and stricter regulations may also mean that older boilers will become obsolete.


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