Greenstar 2000 Combi
Boiler on the blink? If you're looking to diagnose what the problem might be, the first port of call should be your boiler's manual. It's a font of knowledge that will explain fault codes and let you know if you can fix the problem yourself.
If you can't find your manual, most manufacturers will have an online copy available to download on their websites.
To help with diagnosis and prepare you for the likely cost of putting problems right, we've outlined the most common faults your boiler may develop, and how much you should expect to pay for common repairs.
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The majority of serious boiler faults are hard for a layman to diagnose, and if you're not a trained heating professional you should never attempt any repairs that involve removing the boiler casing. It's dangerous to do so and also invalidates any warranty you may have remaining on the boiler.
However, two of the three most common boiler faults can be handled by a competent DIYer and don't always require the attention of a costly heating engineer.
If your boiler loses pressure it could be one of a few things. But most commonly, it will either be a leak, you've recently bled your radiators and the system has lost pressure or your heating has been off for a very long time and lost pressure.
You can repressurise your system yourself by opening the filling loop taps on your boiler until you achieve the desired pressure (usually around one bar). Once this is done, remember to close both taps, at which point your boiler should start to work again.
If your boiler is consistently losing pressure you should have it looked at by a trained engineer to fix the issue for good.
When there's a cold snap, it's remarkably common for a frozen condensate pipe (a condensate pipe is a feature of condensing boilers) to put your boiler out of action. It's not technically a fault with the boiler but if the condensate pipe freezes, the boiler will shut itself down for safety reasons.
Before you incur a costly call-out charge from an engineer, always make sure you've checked that the condensate pipe isn't the problem. Always make sure your condensate is properly insulated with foam, as in the image above, as this should prevent it from freezing in the first place.
Faulty boilers can leak carbon monoxide (CO), a colourless, odourless gas that is produced by incomplete burning of carbon-based fuels. It stops the blood carrying oxygen around the body and can be lethal. According to the NHS carbon monoxide kills around 60 people a year in England and Wales.
Owners of old-fashioned non-room sealed boilers and systems with hidden flues are at a higher risk from the dangers of carbon monoxide. Signs of a boiler CO leak can include dark, sooty staining around it, or a sudden increase in the amount of condensation on the inside of your windows.
You should get a CO detector, and if you live in Scotland you legally need one in your home from February 2022 onwards.
However, don't just buy any old CO detector. Which? testing has uncovered several dangerous CO detectors. Often unbranded and from online marketplaces, our tests have found they fail to alarm even in the presence of large amounts of CO. Check our to know which ones to avoid.
An annual service is also essential to make sure that your boiler remains safe.
Symptoms of CO poisoning can include the following. If you experience these and are concerned they could be linked to CO poisoning, leave the property that has a suspected leak and seek medical help (either from your GP or by going to A&E, depending on the severity).
While frozen condensate pipes, leaking water and dropping boiler pressure are relatively common, there are lots of specific technical faults that can occur with your boiler.
When a part breaks and needs repairing, you'll need a heating engineer to buy and carry out the repair for you.
|Boiler part||Boiler part name||Cost to replace part (including installation)||What this boiler part does|
|Diverter/zone valves||Directs flow of heated water from the boiler for heating or hot water|
|Printed circuit board||The ‘brain’ – it makes things run together|
|Water Pump||Moves heated water from the boiler, for either heating or hot water|
|Fan for combustion||Moves air through the boiler for combustion|
|Gas valve||Regulates gas flow to the burner|
|Overheat thermostat||Prevents boiler overheating|
|Automatic air vent||Lets air out of the boiler|
The average price of a one-off service is £86, according to our 2021 survey of 153 Which? Trusted Trader engineers.
An annual boiler service is the best way to keep your boiler in good working order, to diagnose problems early and limit costly repairs.