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Common Main Boiler Problems & Repair Advice

Rob Wells
By: Rob Wells
Updated: 27th March 2024

Main boilers are normally very reliable but we’re going to take you through the 5 common Main boiler problems you need to know about and how to fix them.

Some of these boiler issues don't neede a heating engineer but if you do need one, get free boiler repair quotes using Boiler Guide.

Common Main boiler problems

Low boiler pressure

Checking a the pressure level of your boiler can be done by taking a look at the built-in pressure gauge, if the needle is pointing anywhere below 1bar then your boiler has low pressure.

How to increase Main boiler pressure

Increasing boiler pressure is something you can do yourself, without the need for a heating engineer, our guide to low boiler pressure can take you through the steps.

Loud boiling noises

When limescale or sludge builds up on your boiler's heat exchanger, they can restrict the flow of water, which then causes the water to steam and boil, something known as kettling.

How to fix loud boiler noises

To resolve the issue, the heating system needs to be cleared of the blockage. To do this, a heating engineer will need to perform a powerflush which involves flucking chemicals through the system.

No heating or hot water

If you’re not getting any heating or hot water there are many possible causes. An error code on the display will help locate the fault, you can find out what Main error codes mean on Boiler Guide.

Some possible causes include:

  • Broken diaphragm
  • Airlocks
  • Thermostat turned down too low or faulty
  • Low boiler pressure

How to fix no heating and hot water

If your central heating isn’t coming on when you expect it to, start out by checking that the temperature is set high enough (18-21°C is an ideal temperature). If some of the radiators are only partially heating up then there might be air in the system and need bleeding. You can check if the boiler pressure is too low by looking at the built-in pressure gauge, take a look at the first Main boiler problem for more details.

Radiators not heating up

If your radiators aren't heating up or are only heating up at the bottom then there might be air trapped in the system which will prevent the water from circulating properly. To release the air, the radiators need to be bled.

How to bleed a radiator

Bleeding a radiator is something you can do yourself and if you feel up to the task then our guide to bleeding radiators can take you through the process.

Leaking and dripping

Most commonly, a leak will be caused by a broken internal component, such as a pump seal or pressure valve. If the leak is coming from the pressure valve, your boiler pressure might be too high. If it's coming from the pump seal, it may have worn out and need replacing.

How to fix a leak

As soon as you spot a leak from your boiler or heating system, turn the mains water supply off right away. Even the smallest of leaks can end up causing damage to your boiler or home. Fixing the part of the boiler where the leak is coming from should only be dealt with by a qualified heating engineer.

Need a boiler repair?



Which Main boiler problems need a heating engineer?

Some of the most common boiler problems don't even need the expertise of an engineer, to help you resolve some faults we've put together the table below.

Problem Possible cause Do you need an engineer?
No heat or hot water Broken diaphragms and airlocks, failure of motorised valves, issues with the thermostat or low water levels Yes
Leaking and dripping Most common cause is a broken internal component but it will depend where the water is leaking from Yes
Banging, whistling or gurgling noises A common cause is air in the system, alternatively it could be that the water pressure is too low or it's kettling Yes
Pilot light goes out Could be a broken thermocouple which is stopping the gas supply Yes
Losing Pressure Could be a water leak in the system, the pressure relief valve needs replacing or due to recently bleeding radiators No, unless there’s a leak
Frozen condensate pipe Your boiler will often display a fault code or warning notification Yes
Thermostat issues Thermostat may be turned off or not set to the correct settings (time etc.) Consider replacing
Kettling Limescale or sludge building up on your boiler's heat exchanger Yes
Radiators not getting hot Sludge or air build up in the system or an unequal distribution of heat You will need to bleed the radiators which doesn't require an engineer unless you don't feel like carrying out the task yourself.
Boiler keeps switching itself off Could be low water pressure, a problem with the thermostat or a lack of water flow due to a closed valve, air or the pump not circulating the water in the system properly Yes

Main boiler warranty

The standard warranty of Main boilers ranges from 3-5 years if you keep up with their terms and conditions, otherwise the warranty will be just 12 months. We've put together a complete guide to Main warranties so that you know exactly what to expect.

Boiler insurance and ongoing cover

If your boiler warranty has expired, boiler insurance could be something worth considering. When comparing insurance, the best ones will include an annual service and safety inspection, so make a note of them. Boiler insurance can be taken out with your energy supplier but isn't compulsory. Look out for boiler insurance and cover that includes an annual service of your Main boiler.

Is it time to replace your Main boiler?

If your Main boiler has been providing heating and hot water to your home for many years, you could be saving up to £300* a year in a detached home just by fitting a brand new boiler. Take a look at the table below to see how much you could be saving depending on your current boiler rating and property.

House Type G (less than 70%) F (70-74%) E (74-78%) D (78-82%)
Semi-detached £195 £140 £125 £110
Detached £300 £210 £165 £135
Detached bungalow £155 £110 £100 £90
Mid-terrace £170 £120 £105 £95
Mid-floor flat £80 £55 £50 £45

Finding the best heating engineer for a Main boiler replacement

After deciding that you'd like a new boiler installed, you have to decide who you like to carry out the installation and your choice will come down to a local engineer or a national company.

Branded manufacturers may be slightly more expensive, they can provide extra services such as ongoing boiler cover. You'll also have big brand protection which is a huge bonus.

Meanwhile, local engineers can offer very competitive rates and you'll get a personal service throughout your communications. It's always a good idea to get a quote from more than 1 engineer to make sure you're getting the best deal, we recommend getting up to 3.

Send us an enquiry today to receive free quotes for a new boiler and find trusted engineers near you with our free service.

*According to the latest figures from the Energy Saving Trust

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Rob Wells

About the author

Rob Wells

Rob is another of our resident home heating experts. He manages our external partnerships, making sure you get the most up to date information.

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