What the quote in front of you should say
Ask your installer to put the job in writing: what's being fitted, who's doing the work, and what you'll get once it's finished. A good quote names a specific set of things before any work begins, so you can check it against what turns up on the day.
The appliance and its efficiency figure
Ask your installer to name the exact boiler going in, by make and model. They should also write down its efficiency figure for building control, and that figure is not always the one printed on a manufacturer's brochure. Ask your installer which number they mean. We explain how to tell the two apart in our guide to efficiency figures.
The components around it
A boiler is rarely the only part of the job your installer answers for. Where the flue goes is one example. Your installer checks the distance against Approved Document J and against the boiler manufacturer's instructions, and some of those distances have exceptions.
For a few, the final route is a judgement your installer makes on the day. Ask them to walk you through it, because that is a genuine answer and not a gap in the quote. We set out the distances and exceptions in our guide to flue position.
The notification route
Someone has to tell the building control body the work happened. For most gas and oil boiler jobs, your installer self-certifies (signs the work off themselves, through their own competent-person scheme). Ask your installer which route they use. Ask them to name the certificate you should receive once the job is signed off.
The edition it is working to
Right now, your installer should be working to the 2021 edition of Approved Document L, with its 2023 amendments. The 2026 edition takes effect on 24 March 2027. If your installer notifies building control before that date, your job stays under the 2021 edition, as long as work starts before 24 March 2028.
Ask your installer to name the edition they're working to, so you can check the efficiency figure and the controls against the right version of the rules. Check which edition applies to your own job in our guide to which edition applies to your job.
What your boiler quote should name
Hold each of these against the quote in front of you. If your installer hasn't named one, ask them to add it before you agree to anything.
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A Gas Safe registered business
Look for the installer's registration number on the quote, and check it against the Gas Safe Register before the work starts.
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The boiler's efficiency figure
Ask your installer to name the efficiency figure for the new boiler, measured as the regulations measure it.
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The controls fitted alongside the boiler
Look for a timer, a room thermostat, thermostatic radiator valves and a boiler interlock named individually.
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An extra measure, if it's a gas combi
Ask your installer which extra efficiency measure the new combi comes with if the quote doesn't name one.
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A system flush with inhibitor
Ask your installer to flush and clean the existing system and add inhibitor, to BS 7593, and to put this in the price.
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Where the flue will go
Ask your installer to name the planned route and termination point for the flue before they start work.
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Who notifies building control
Ask who notifies building control and when, since this is usually done through your installer's own competent-person scheme.
A missing line isn't proof the job is wrong. It's a reason to ask your installer to add it before you sign.
Where the rules leave it to the installer
When you get a quote, some parts of the job have a number attached: a distance, a material or a figure you can read in Approved Document J or Approved Document L. Other parts, your installer decides on the day, using their own judgement. There's no number to check a judgement call against, and that's not a fault in the job, just a different kind of decision.
What's fixed, and what's left to your installer
Flue clearances are a good example of a fixed number. The distance your installer has to keep between the flue terminal and a window, a door or a boundary is set out in Approved Document J, alongside the manufacturer's instructions for the boiler going in. We explain what that looks like in our guide to flue position and the rules that govern it.
Your installer decides the exact path the flue takes through your building, and how they sequence the work on your job. They make that choice within whatever clearances apply to your boiler and your property.
What this means for your quote
When something comes down to judgement, don't expect a citation next to it, because there isn't one to give. What you can ask your installer to show you is the route they've chosen, the reason for it, or a simple note confirming the position keeps the right clearances.
A quote that names a fixed requirement but gives you nothing behind it is a different problem from one that stays quiet on a judgement call. Ask about the first. The second is often just how that part of the job works.
Who signs off this part of the job
Your installer can self-certify some of this work, which means they sign off the work themselves through their registration scheme. They should send you the paperwork for it once the job is done.
For gas work, check that your installer is Gas Safe registered. Gas Safe Register is the statutory register of gas engineers in Great Britain, at gassaferegister.co.uk.
What to ask if something's left open
If a line in your quote reflects your installer's judgement rather than a stated figure, that's not a problem on its own. Ask about it if you can't tell from the quote what they decided or why.
Ask your installer to show you the route they've chosen for the flue and the clearance they're keeping to. We explain how to read a quoted number against what's required in our guide to efficiency figures, so you've got something to compare it against.
Questions about your quote checklist
What should an installer's quote name?
Ask your installer to put the following in writing before you agree to the job: the boiler they're fitting and the efficiency figure they're quoting for it, the controls they're fitting, how they'll clean and treat the system, where the flue will go, how they'll notify building control, and which edition of Approved Document L they're working to. If your installer leaves any of this out, ask them to add it before you sign.
What should I ask if something is missing from my quote?
Ask your installer to name it. If they haven't given an efficiency figure, ask which measure they used to reach it. If they haven't listed the controls, ask what they're fitting and, for a gas combi, which extra measure comes with it. If they haven't named the flue route or how they'll notify building control, ask them to confirm both before the job starts. You're agreeing to this quote, so ask your installer to fill in anything missing before you sign it.
Does the installation need a power flush?
Under Approved Document L, your installer needs to clean and flush the system, then dose it with inhibitor, to BS 7593, before fitting the new boiler. A power flush is one way installers do that, but what's required is the cleaning done to BS 7593, not that particular method. Ask your installer to confirm they'll flush and treat the system to BS 7593, and which inhibitor they're using.
What if the quote doesn't name any controls?
A replacement boiler needs a set of controls: a timer or programmer, a room thermostat, thermostatic radiator valves on the other rooms, and a boiler interlock that stops the boiler firing when nothing's calling for heat. If the new boiler is a gas combi, your installer also needs to fit one of four extra energy-saving measures. If your quote doesn't name any of this, ask your installer to list the controls and, for a combi, which extra measure they're fitting.
What does it mean if the quote doesn't say which edition of Approved Document L it's working to?
If you're getting quotes today, you check your installer's work against the 2021 edition of Approved Document L, as amended in 2023. The 2026 edition takes effect on 24 March 2027. If your installer notifies building control before that date, you still work to the 2021 edition, as long as the job starts before 24 March 2028. An installer who names the edition has checked which one applies to your job. One who hasn't may still have got it right, but you've no way to see that from the quote in front of you. We set out how the two editions relate in What the Building Regulations Require of a Boiler Installation, and what changed between them in What Changed in the 2026 Edition of Approved Document L.
What if the quote doesn't say where the flue will terminate?
Flue position comes with minimum distances from openings, boundaries and other features, and your installer sometimes has to use their own judgement on the exact route within those distances. If your quote names the planned termination point, you can check it against those distances yourself. We explain what governs each distance and each exception in Boiler Flue Position.
What if no efficiency figure appears on the quote?
The efficiency figure the regulations use isn't always the same number a manufacturer prints on its own product page. If your installer gives you a figure without saying which measure it is, you can't tell much from it. The minimum a replacement gas boiler needs to reach, in Approved Document L's Table 6.2, is 92%, measured as efficiency is defined under ErP. Ask your installer to state the figure that meets this minimum. We explain the regulated metric and work through a real quote in Boiler Efficiency Figures.
If an item is missing from the quote, does that mean the installation itself won't comply?
What the regulations require of the job and what your installer writes on the quote are two different things, so a missing item doesn't settle the question either way. Whether a specific installation meets the regulations is a decision for the installer's competent-person scheme or for the building control body. A missing item just means you can't check the job against the rule yet, so ask your installer to add it.