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Your boiler questions answered

Your boiler questions answered

Which? heating expert Matt Knight shares his knowledge on everything from boiler servicing to how much it should cost to get a boiler repaired

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By Ross Barnard

Read more: - Which?

The darker evenings are setting in, temperatures are dropping and the annual autumn dilemma is on everyone’s lips: shall we turn on the heating?

The hope is that the boiler will fire up the second the switch is flicked. If the dreaded happens and it doesn’t come on, the best scenario is that it can be fixed easily; the worst being that the boiler needs to be completely replaced.  

But even if your boiler seems to be working as it should, you’ll want to get it serviced annually to make sure it’s in tip-top condition.

I caught up with our heating expert Matt Knight to answer your common boiler-related questions, from how much you should spend on a service and repairs to which boiler brands are hardest to fix. 

Jump straight to our boiler brand reviews to find the best How often should I get my boiler serviced and how much should I expect to pay? It should cost around £80 to get your boiler serviced and you need to have it done once a year. Not doing so will almost certainly invalidate any warranty that you might have remaining on your boiler, not to mention that annual checks will hopefully pick up small bits of wear and tear, such as corroded washers, before they become bigger and more expensive problems.

See how to get the best boiler service. An annual service can also pick up potentially dangerous faults, like carbon monoxide leaks, which can be fatal. We would also strongly recommend buying a carbon monoxide alarm. According to a survey of the general public we conducted in July 2018, more than a third of people (36%) still don’t have a carbon monoxide alarm in their home. You can get a Best Buy alarm from as little as £15.  How much is it likely to cost to get a boiler fixed, on average? To get the answer to this question, we ask almost 200 expert heating engineers every year how much they would charge for parts and labour to fix the most common boiler faults. See which boiler parts we ask about in the infographic below. 

On average, expect a repair to cost in the region of £200, but it varies depending on what has gone wrong. According to our boiler reliability survey, only 52% of boilers from the least reliable brand are fault-free after six years, compared with 83% for the most reliable brand. So if you don’t want the ongoing hassle and cost of repairs, it really does pay to buy from one of the most reliable manufacturers.  Log in now or become a Which? member to unlock the prices below in our guide to common boiler problems and repair costs. Which boiler brands are the hardest to source spare parts for? This should be an important consideration when you’re buying a new boiler. If your boiler breaks, you’ll want it back up and running as soon as possible. Having to wait a few extra days for the correct part is going to feel like a lifetime if you’re living in a freezing-cold house and enduring cold showers.  In our annual boiler reliability survey, heating engineers tell us that it’s easy to get hold of spare parts for big boiler brands such as Worcester Bosch and Vaillant, but much harder for brands like Ferroli. You can see how each manufacturer measures up for this score in our boiler reviews. 

Are there any boiler faults that it’s easy and safe to fix myself? No-one other than a Gas Safe registered heating engineer should ever attempt to fix your boiler; it’s dangerous and it will invalidate your warranty. You can use Which? Trusted Traders to find a fully qualified and vetted heating engineer. Having said that, if your condensing boiler has stopped working during a cold snap, it’s worth checking whether the condensate pipe (the small external white pipe that takes condensate from the boiler into an external drain) has frozen up. If it has, you can restore the boiler to working condition by thawing out the pipe. Find out how to do this properly by watching our online video.

Another relatively easy fix is to top up the boiler pressure if it’s dropped well below 1 Bar. You can do this by waiting for the water in the system to cool, then opening the taps on the boiler’s filling loop until the pressure reads 1 bar, or a little above. If you find yourself doing this regularly, there might be a small leak somewhere in the system, which you will need to get a professional to check out. See our common boiler problems page for more information. What types of boiler are there and which one is best for my home?

If, like most people in the UK, you’re connected to the gas mains, or you’re ‘off grid’ and need an oil boiler, you can pick between three different types to best suit your needs:  Combi boilers These are the most common type of boiler in the UK, but they’re not necessarily the best fit for every home. 

Combination boilers heat hot water on demand and don’t require extra space for a hot water cylinder. They’re a good choice if you live in a small home with limited space, or if you have a relatively low hot water demand.  However, if you often require hot water to be delivered to more than one location simultaneously, then you should look at either a heat-only or a system boiler. 

Heat-only boilers Sometimes also known as regular boilers, heat-only boilers heat hot water and store it in an insulated cylinder for use when it’s needed. They’re a better choice for large homes that have multiple bathrooms, as switching on the hot tap in one location won’t lead to a drop in pressure or temperature of the water in another.  But these types of boilers need a lot of space in your home. You’ll need space for two feed tanks in the loft, and an airing cupboard for the hot water cylinder.

System boilers They have all of the benefits of a heat-only boiler but take up less space as they don’t require a feed tank in the loft. And because they operate as a sealed system, they’re also particularly good if you live in an area with low water pressure.  System boilers do still have a hot water cylinder that stores heated water, and so are better equipped than combi boilers to provide hot water to more than one location at the same time. 

Read more about the different types of boiler in our dedicated guide. Which boiler brands are the best? Every year, we conduct a general public survey with almost 8,000 people who have purchased a brand new boiler within the past six years, to find out which are the best and worst boiler brands. By asking boiler owners directly how often, if at all, their boiler has broken down, and generally how satisfied they are with it, we can give every boiler brand in the UK that has a greater than 1% market share an accurate reliability and customer satisfaction rating. 

We also survey almost 200 expert heating engineers who work on boilers every day to ask them for details on each brand, including their view on its build quality, whether they would recommend it to a customer, how easy it is to repair and service, and how easy it is to get hold of parts and spares.  By conducting these two surveys we can provide a well-rounded and independent review of almost every gas and oil boiler brand on the market.  Which? members can see how 17 gas boiler brands and two oil boiler brands fare in our surveys, before they buy a new boiler. Almost half (48%) of the people who buy a boiler from the least reliable brand need to have it repaired in the first six years of ownership, compared with less than one in five (17%) who buy the most reliable. 

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