Back Boiler Replacement Guide [2023] Re February 3, 2023

Back Boiler Replacement Guide [2023]

Man fitting a boiler

How do I get my back boiler replaced?

In this guide, we’re going to hold your hand and lead you through the process of replacing a back boiler. Back boilers are becoming an increasing rarity as they are incredibly inefficient and as they are not installed anymore you can no longer get parts for them if they break down.

Replacing a back boiler can be a bit of an undertaking and there are lots more questions to answer as a customer looking to replace a back boiler – ‘Will they have to rip my fireplace up?’,  ‘Will I need to have my system re-piped?’, and most importantly, ‘How much will it cost to replace my back boiler?’.

Don’t worry, we’ll answer all these questions and give you an idea of how much it will cost and the kind of disruption you can expect when swapping your back boiler for a new combi boiler.

What is a back boiler?

A back boiler is an outdated form of boiler no longer in production that is located behind a gas fire in the chimney breast. They were introduced in the ’60s and really took off as people were replacing coal/wood open fires with more modern gas fires, which were more convenient and energy-efficient.

Removing an open coal or wood fire left a large space in which the back boiler filled nicely, so they became the ideal evolution in home heating. The chimney acts as a natural flue for the back boiler too, perfect right? Well, for the ’60s maybe, even the ’70s & ’80s but in modern ages, the back boiler has been left behind in terms of energy efficiency and productivity by combi boilers.

Back boilers haven’t aged as well as some other classics.

Back boilers are no longer fitted by heating engineers as regulations regarding energy efficiency have rendered them obsolete.

Why should I replace my back boiler?

We understand the attachment to your old back boiler. They really were built to last, giving over 25 years of faithful service, compared to the 10-15 years of service you can expect from a decent combi. If you still have a back boiler then there’s a good chance you have an insanely popular Baxi Bermuda back boiler, these back boilers dominated the market back in the day. Another popular back boiler was the Glow Worm back boiler, not in the same league as the Baxi Bermuda but also a solid pick.

Given the length of service and reliability, why would you choose to replace your back boiler? Well, there are a few reasons why you would…

  • Energy-efficiency
    Back boilers are incredibly inefficient when compared to modern combi boilers. Back boilers are around 78% energy-efficient, while modern combi boilers are over 90% efficient. Government regulations require a boiler installed to be over 86%. So even if you wanted a new back boiler installed, it wouldn’t be possible. You can have a look at our most energy-efficient boilers here.
  • Saving on utility bills
    You can expect to save around £300 per year when replacing a back boiler with a combi boiler. In the point above we mentioned back boilers are only 78% efficient, so 22% of your heating bill is just wasted energy. Here are 5 ways to save money on your heating bill.
  • Environmentally friendly
    A modern combi will save you a lot of money on heating and it will also be better for the environment due to increased energy efficiency.
  • Spare parts
    As back boilers are no longer manufactured, neither are their parts. So if something goes wrong with your back boiler then you will either struggle to find the part or have to wait a few weeks until it comes in. You don’t want to be in a position where your heating goes down before you find out that you need a new back boiler.
  • Safety
    As the parts are no longer produced there is a chance that an engineer may try and fix your back boiler with a similar part not built specifically for your boiler. It’s not a good idea to mess about with gas and given that back boilers have a maximum lifespan of 30 years, even the ones installed in the ’80s have served their time. If you still have a back boiler, you’re better off getting it replaced on your own terms rather than waiting for it to let you down.
  • Home aesthetics
    If you have a gas back boiler you’ve probably got one of those old-fashioned gas fires in front of it messing up that design flow in your living room that you’ve cultivated so fastidiously. Don’t let that gas fire hold your creativity back, get rid of that gas boiler and the gas fire and modernise!

Back boiler pros and cons

  • 1960s classics
  • Built with fewer components
  • Could be tucked away out of sight behind a fireplace
  • Outdated
  • Not as energy-efficient as a modern condensing boiler 
  • Spare parts are very hard to find
  • Harmful to the environment
  • Safety concerns, especially around carbon monoxide poisoning 
  • Back boilers are open flued, meaning they need fresh air to work properly. You’ll be at risk of a toxic fume build up if there is a problem with your chimney or boiler.

  • The boiler’s ventilation system can contribute to draughts and noise.

  • These boilers rely on a chimney for ventilation. This limits your design choices when you revamp your fireplace.

How much of a mess will replacing a back boiler cause?

There are two ways of replacing a back boiler. In most instances, we would remove the back boiler and cap off the gas supply. This way you regain the space behind the fire, you could open up the chimney again, install a log burner – whatever works for you. It’s also better to remove the appliance if possible, you don’t want it living behind the fire rusting away.

In certain circumstances where it would cause structural damage to remove the back boiler (if the back boiler has been bricked in or a fireplace has been built around it) then it may be possible to isolate the back boiler from the electric, gas and water supplies and leave it in place.

It’s not an ideal solution but sometimes it can be preferable to the upheaval of smashing up a fireplace and unleashing 30 years of dust and whatever else is behind your chimney.

Another factor to consider when replacing a back boiler is the hot water storage cylinder, usually located in an airing cupboard. Unlike a combi boiler, which heats water as and when it’s needed, a back boiler works like a system boiler, heating water and storing it in a tank until you need it. 

When replacing a back boiler you can choose to replace the storage tank at the same time and reclaim your airing cupboard too. There is obviously some upheaval with removing all the pipework and tanks from your previous system but if you’re switching to a combi system there is no longer any need for it.

You may decide to switch from a back boiler to a system boiler if you have high heating demands (large family, multiple bathrooms used simultaneously), in which case the tank will not necessarily be removed.

If you aren’t sure what type of boiler you want to switch to then we have already explained the different boiler types and the advantages and disadvantages of each type in another article.

Removing a back boiler and all the associated pipes and tanks is an undertaking and it will inevitably kick up some dust and debris but our engineers will cover the areas in which they work to minimise the mess as much as possible.

How long does it take to replace a back boiler?

A back boiler replacement can take between 2-3 days depending on what the job entails. Often you can’t tell until you take the gas fire out and look at the back boiler itself how easy it will be to remove (or difficult).

Replacing a back boiler for a combi is the most difficult installation job as it requires removing the gas fire, removing the back boiler, rerouting the pipework to wherever the new boiler will be located, installing a flue for the new boiler and removing any old tanks and pipework no longer required.

We’ve written an article covering how long it takes to replace a boiler, looking at combi, system and regular boilers. That goes into a bit more depth about how long it will take to replace different boiler types but we usually estimate 2 days for a back boiler replacement but if difficulties are encountered then keep in mind it could take up to 3 days.

This is disruptive but when the job is done you will have a much more efficient heating system and you will immediately start saving money on your heating bills.

How much will it cost to replace my back boiler?

A new replacement boiler will vary in costs depending on what company you choose but prices at WarmZilla start at £2,589.00 or £17.04 on monthly finance – that is an exceptionally good price if we do say so ourselves*.

Elsewhere you will be looking at spending well over £3,000, possibly even £4,000. Remember, WarmZilla offers a Best Price Guarantee’. If you find a cheaper quote elsewhere on a like-for-like boiler we’ll beat it by £50.

In the example below you can see that we have completed a WarmZilla survey, in just a couple of minutes to get a price on switching out a back boiler for a new combi boiler and it costs a very reasonable £2,589.00 or £17.04 per month boiler finance.

This price is on a premier Worcester Bosch boiler with a 5-year guarantee, smart thermostat, system filter, system cleanse, removing of all old pipework and back boiler, flue installation, and everything you need to get your boiler up and running.

So if you’re paying boiler cover to keep your old back boiler running, stop. It’s a false economy, you’re better off just replacing it and enjoying the savings on your heating bills and boiler cover (with your new 5-year guarantee).

If you want a longer-term guarantee we can offer the same model as the one in the example above with a 10-year guarantee for £2,779.00 or £19.54 per month on boiler finance. Both these examples are based on a ten-year payment term and paying half the cost of the boiler as a deposit. Some of you will be paying more than the monthly finance cost on boiler cover on an older boiler.

If you don’t have the money laying around to cover half the payment as deposit, then don’t worry – just choose £0 deposit on our finance calculator and if you choose to pay over ten years the monthly repayment will be £36.57.

It really depends on how long you want your boiler finance to last but hopefully, it’s not as expensive as you thought it might be to replace your back boiler.

To get an exact price and have a play around with the finance calculator to find a package that suits your budget, you can find your new boiler now.


Whilst replacing a back boiler may seem like a bit of an undertaking (we can sense your anxiety levels creeping up already), it probably won’t be as expensive or disruptive as you fear. 

You know it will need to be done eventually but you can think of plenty of reasons why it doesn’t need to be done now, we get it. Who needs the stress? Do you know what’s more stressful? Waiting until your back boiler breaks down and you can’t get a part in the dead of winter because they no longer make them.

Even the youngest of back boilers are reaching the end of their lifespan now, we would recommend getting a quote on replacing your back boiler, it only takes a couple of minutes and we have flexible boiler finance plans so you can spread the payments to an amount that’s affordable for you.

All WarmZilla engineers are Gas Safe registered and will always do their very best to protect your home while working by putting down coverings in areas they are working in.

If you have any questions regarding your back boiler, please contact us. We’re always happy to provide free advice and you’ll always be speaking to a Gas Safe registered engineer who knows what they’re talking about, not a customer service advisor who doesn’t. 

*Prices correct at time of blog publication

  • December 23, 2022, 9:46 pm

    Yes we have to dig out our poor old back burner, it was a New World a long time ago. I gave it a good clean up, the burner fires up but it won’t regulate properly, the fire is ok. we have an emersion so we have some heat & hot water. we have 7 rads 1 bathroom & 3 beds. Even the gas oven has gone out in sympathy, it must be jinxed. thanks P&D Wilson. Happy Christmas.

  • January 4, 2023, 8:16 am

    Hi Patricia, it’s always tempting to leave a back burner in place, they do last a very long time. They are really inefficient though, you could save up to £400 a year on your energy bills by switching to a modern combi boiler. You can get an instant quote online from the WarmZilla site – Hope you had a lovely Christmas and New Year.

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