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Common Keston Boiler Problems & Repair Advice

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

Last Updated: 12th January 2022

Keston Boiler Repair

Should something go wrong with your Keston boiler, this handy guide of common Keston boiler problems will help you find out how to fix them and whether you can do so without a heating engineer. If in doubt though, always get in touch with an engineer, you can get a free boiler repair quote with our service.

Common Keston boiler problems

Ignition failure (E01 or E02)

After failing to ignite 5 times, some Keston boilers will display the E01 error code. The first thing to do is check the gas supply is on, if it is, then there are many possible faults that could prevent the boiler from igniting: blocked flue, blockage in the condensate pipe, insufficient gas supply, faulty fan.

How to fix ignition failure

To successfully diagnose the error, you’ll need to hire a Gas Safe registered engineer, who will then be able to repair the fault to get your boiler igniting again.

No hot water but heating works

Keston combi boilers have diverter valves that direct hot water to either the central heating system or the hot water tap, depending on which you’ve turned on. Chances are, the diverter valve is stuck, meaning that all the hot water is being sent to the radiators rather than the taps.

Fixing the hot water

It’s possible that a heating engineer will be able to get the diverter valve working again but it might need replacing. You'll need to hire a Gas Safe registered engineer to either repair or replace the diverter valve.

Radiators not heating up

If your radiators aren't heating up or are only heating up at the bottom then there’s a good chance that there’s too much air in the system, preventing the hot water from circulating around the radiators. To remove this excess air, the radiators need to be bled.

How to bleed a radiator

Bleeding a radiator is something you can do yourself by following our guide to bleeding radiators but don’t hesitate to contact a qualified heating engineer to do it for you if you don’t feel confident.

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Low boiler pressure (F1)

Low boiler pressure, or low water pressure, means that there isn’t enough water pressure in the system. Checking a boiler's pressure level is simple to do, simply take a look at the built-in pressure gauge and if it's below 1 bar then the boiler has low boiler pressure. On Keston C40 and C55 combi boilers, you’ll see the E44 error code to let you know there’s low water pressure.

Increasing boiler pressure

Low pressure needs to be increased to something more sufficient (between 1 and 2 bar), any higher than 2 and you’ll have the opposite problem as the pressure will be too high. Increasing boiler pressure is something you can do yourself by following our guide to low boiler pressure.

Loud noises from the heating system

If you're hearing a noise that resembles a kettle boiling then limescale, sludge or debris might have built-up on your boiler's heat exchanger, which is known as ‘kettling’. This buildup restricts the flow of water within the heat exchanger, causing the water to overheat, steam and make sounds similar to a kettle.

How to remove the blockage

A Gas Safe registered engineer will be able to perform a powerflush, a process that involves chemicals being circulated around the heating system, which will clear it of any debris.

High boiler pressure (E40)

Boiler pressure is too high when the needle on the pressure gauge reaches the red area. A boiler with too much pressure puts unnecessary strain on the unit and could lead to damage.

As boilers operate the pressure will increase a small amount, by around 0.3 bar, but if it’s increasing by 1 bar then the pressure release valve, designed to manage excess pressure, could be faulty.

Fixing high boiler pressure

A Gas Safe registered engineer will need to fix or replace the pressure valve if the pressure is rising a lot during operation. Alternatively, water will need to be released from the system, which will lower high pressure. You can do this yourself in the same way as bleeding a radiator, but rather than doing this for air to escape, you’re looking to release water. Ideal boiler pressure should sit at around 1.3 bar.

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Which Keston boiler problems need an engineer?

In the table below, we've listed the most common boiler problems and what might be causing them. Take a look to know if you'll be needing an engineer or not.

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 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

Keston boiler warranty

Keston boiler warranties vary depending on the model you purchase but since 1st January 2018, the standard warranty of their Combi and System boilers has been increased to 5 years. We've put together a complete guide to Keston warranties so that you know exactly what to expect.

Hire a Gas Safe engineer to carry out an annual service of your Keston boiler to keep the warranty valid and make sure the unit is running safely and efficiently.

Boiler insurance and ongoing cover

If your boiler warranty has expired, then boiler insurance is a possible option. You can take out insurance with your energy supplier but you're absolutely no obligation to do so. When comparing insurance, the best ones will include an annual service and safety inspection, so keep an eye out for them.

Is it time to replace your Keston boiler?

If your Keston boiler has been heating your home for a number of years, then you might be thinking about getting a new one as you could be saving up to £365* a year in a detached home. 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 (< 70%) F (70-74%) E (74-78%) D (78-82%)
Semi-Detached £240 £170 £150 £135
Detached £365 £255 £205 £165
Detached Bungalow £190 £135 £120 £105
Mid Terrace House £205 £145 £130 £115
Flat (Mid Floor) £95 £65 £60 £50

Figures are for England, Scotland and Wales only*.

How to find the best Keston boiler installers

Deciding who to replace your boiler can be a big decision as you want to make sure that you're getting the best deal possible. The choice here comes down to a local engineer or national company.

Local engineers can come with very competitive rates and if you like a personal service then you're likely to talk to the same person throughout. 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.

Branded manufacturers may be slightly more on the expensive side, you'll have big brand protection which is a huge bonus and they can offer extra service such as ongoing boiler cover.

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


Data Source: Energy Saving Trust, Heating Your Home: Boilers (2022)
*Based on replacing an old gas boiler with a condensing A-rated boiler with thermostatic radiator valves, programmer and room thermostat in a detached home. Figures are based on fuel prices as of November 2021.

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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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