By Boiler Quotes Editorial Team · Updated 15 August 2026
What a Proper Quote Itemises
Ask every installer for the same list and the comparison does itself. A quote worth taking seriously names the appliance, the parts, the labour and the total, so you can lay three of them side by side and see where they actually differ.
| Line | What it should say |
|---|---|
| Boiler | Make, model and output, for example a named 30kW combi. Not "supply and fit new combi boiler" |
| Flue | Standard kit, plus any extension, plume kit or vertical flue the job needs |
| Controls | The thermostat by name, and whether it is programmable, smart or wireless |
| Filter | A magnetic system filter, named. Most manufacturers require one for the full warranty |
| System cleanse | Chemical flush or power flush, stated explicitly, plus inhibitor |
| Labour | Days on site and how many engineers |
| Making good | Removal and disposal of the old boiler, pipework boxing, any plastering |
| Warranty | Length in years, and who registers it with the manufacturer |
| Total | One figure including VAT, with the deposit and payment stages set out |
| Timescale | A start date and how long the work takes |
If a quote is a single number on headed paper, you have nothing to compare. Ask for it itemised before you go any further.
Compare Like for Like Before You Compare Price
Two quotes that differ by several hundred pounds usually differ in scope rather than value. The gap is almost always one of five things.
Boiler tier. Manufacturers run budget, mid and premium ranges. A cheaper range from the same brand is not a worse boiler for every home, but it is a different product with a different warranty.
Warranty length. The same boiler can carry very different warranties depending on the installer’s accreditation with that manufacturer. This is the single biggest hidden difference between two quotes for the same appliance.
System cleanse. A chemical flush and a full power flush are not the same job and do not take the same time. One quote including a power flush and another including neither can look like a price difference when it is a scope difference.
Controls. A basic programmer and a smart thermostat are separated by a meaningful amount of money.
Position. Moving a boiler from an airing cupboard to a kitchen wall adds pipework, making good and time. Our boiler installation cost guide breaks the labour element down by job type.
The Questions Worth Asking
Six questions separate a firm quote from an optimistic one.
Is this a fixed price or an estimate? A fixed price survives what the engineer finds behind the old boiler. An estimate does not.
Who does the work? Some companies quote and then subcontract. Ask who turns up and whether they are employed or self-employed.
What is your Gas Safe registration number? Every engineer working on gas must be on the register, and you can check the number yourself. Our guide to the Gas Safe Register covers how.
Who registers the warranty and notifies Building Control? Both are the installer’s job. In England and Wales the installation has to be notified to Building Control within 30 days, after which you should receive a Building Regulations compliance certificate. Keep it with the warranty paperwork, because a buyer’s solicitor will ask for it.
What happens if you find a problem? Ask what the hourly rate is for anything outside the quote, and get the answer in writing.
What is not included? The most useful question on this list, and the one most people forget.
What Quotes Commonly Leave Out
None of these are dishonest omissions. They are things an installer cannot see until the old boiler is off the wall, which is exactly why they belong in a conversation before you sign.
- Gas supply pipe upgrade. A higher output boiler can need a larger gas pipe run back to the meter. On a long run through a finished house this is real money.
- Condensate route. A condensate pipe needs a fall to a drain. Where there is no easy route, a pump is added.
- Asbestos. Common around older flues and in some airing cupboards. Removal is a specialist job and is never part of a boiler quote.
- Removing an old cylinder and tanks. Converting to a combi frees up a cupboard and a loft tank, but taking them out and making good is separate work.
- Scaffolding. Occasionally needed for a flue at height.
- Decoration. Very few quotes include redecorating after pipework has been chased into a wall.
Red Flags
Walk away, or at least slow down, if you see any of these.
- A price with no boiler make and model on it.
- A discount that expires today, or pressure to sign during the visit.
- A large deposit before any materials are ordered.
- Cash only, or a reluctance to put the quote in writing.
- No Gas Safe registration number offered when you ask.
- A quote well below the other two with no explanation of what is different. Ask what has been left out before you assume you have found a bargain.
Warranty Is Part of the Price
Warranty length varies more between quotes than most people expect, and it is worth real money. The difference between a five year and a ten year warranty on the same appliance is five years of parts and labour you either have or do not.
Two conditions usually apply. The boiler has to be registered with the manufacturer shortly after installation, and it has to be serviced annually by a Gas Safe registered engineer with the service recorded. Missing a service does not usually void the warranty outright, but it can lose you cover for any fault that service would have picked up. Our boiler warranty guide goes through what the longer warranties actually require.
A Worked Example
Take a three bedroom semi with one bathroom, swapping an old combi for a new one in the same position. Three installers visit and all three quote for "a new combi". Here is where the money actually goes.
| Quote A | Quote B | Quote C | |
|---|---|---|---|
| Boiler range | Budget | Mid | Mid |
| Warranty | 5 years | 10 years | 7 years |
| System cleanse | Chemical flush | Power flush | Not stated |
| Controls | Existing reused | Smart thermostat | Programmer |
| Magnetic filter | No | Yes | Yes |
| Old boiler removed | Yes | Yes | Not stated |
Quote A is the cheapest and is quoting a different job. Quote B is the most expensive and includes two things the others do not. Quote C has two blanks, and until those are filled in it cannot be ranked against either.
The useful move is not to pick the lowest number. It is to go back to A and C and ask what they would charge to match B, then compare again. Installers expect this and it is a normal conversation to have.
Before the Visit
Have these ready and every quote you get will be more accurate, which means fewer surprises later.
- The make and model of your current boiler, off the front panel.
- Number of bedrooms, bathrooms and radiators.
- Where the boiler is now, and whether you want it moved.
- Your water pressure at the kitchen tap, if the engineer asks.
- Any known issues: a slow radiator, a noisy pump, a cupboard you suspect has asbestos in it.
If a quote arrives without anyone having asked about radiators or bathrooms, treat the number with caution. Output cannot be worked out from the outside of a house.
How to Decide
Line the three quotes up against the table at the top of this page and fill the gaps by asking. Once every quote covers the same work, the same boiler tier and the same warranty, the cheapest one is genuinely the cheapest one.
If the boiler being proposed differs between quotes, check the output suits your home before you weigh the prices. A quote for the wrong size boiler is not a cheap quote. Our boiler sizing guide covers how output is worked out from bedrooms, bathrooms and radiators.
Finally, judge the installer as well as the paperwork. The person who measured up properly, answered the awkward questions and put the exclusions in writing is usually the one whose price holds.
And if you plan to pay monthly, read our new boiler finance guide before you sign, so the APR gets compared as carefully as the boiler.
