What You Need Before You Start Quoting
Turning up to a boiler survey without the right information is the fastest route to underpricing a job. Before you can put a single number on paper, you need to understand what you are actually being asked to install, where it is going, and what is already in the building. This is not just good commercial sense. Under the Gas Safety (Installation and Use) Regulations 1998, specifically Regulation 36, you are responsible for ensuring that any gas appliance you commission is safe to use. If you have not properly assessed the installation conditions, you cannot make that determination.
Arrive at the survey with a notepad, a tape measure, a torch, and a short checklist. You want to record the existing boiler make, model, output, and age. You want to look at the current flue route and note whether it is rear, side, or vertical. Check the gas meter size and the incoming pressure, because on some older properties the existing supply will not cope with a larger modern boiler without a pipework upgrade. Look at the system type (open vented, sealed, gravity fed) and the radiator count, because converting from a regular to a combi will need every radiator checked and the system flushed.
Also record any access constraints. Is the old boiler in a tight airing cupboard? Is there a bedroom above that means you will need to notify the Building Control under Part L of the Building Regulations? Noting these now means your quote reflects reality, not a best-case scenario.
- •Existing boiler make, model, output (kW), and approximate age
- •Current flue position and route, including any obstacles
- •Gas meter size and incoming supply pressure reading
- •System type: combi, regular, or system boiler
- •Radiator count and condition of pipework
- •Access constraints: loft hatch, airing cupboard, ceiling voids
- •Location of existing gas inlet and stop valve
- •Whether the property is rented (changes your obligations significantly)
Step 1: Scope the Job Precisely
A quote is a legally binding offer once the customer accepts it. Under the Consumer Rights Act 2015, section 50, any information given to a consumer before a contract is formed becomes part of the contract. That means if you tell the customer during the survey that the price includes new pipework to the cylinder, that commitment is enforceable even if you forgot to write it down. Your first job is therefore to define with absolute clarity what you will do and, equally important, what you will not do.
Break the scope into three categories. First, the core installation: supply and fit of the named boiler model, new flue, new gas connection to the existing meter outlet, new condensate run to an internal waste. Second, associated works: power flushing the existing system, fitting magnetic filter, fitting room thermostat and programmer, capping redundant pipework. Third, exclusions: any re-routing of radiator pipework, decorating after the job, electrical consumer unit work.
Being explicit about exclusions is where most disputes start. If you write 'supply and install Worcester Bosch 4000 30kW' and say nothing else, the customer will assume that includes draining down, moving a towel rail, and making good the kitchen floor. Write it all down, in plain English, section by section.
- •List every item of work you WILL do, with the specific product model and spec
- •List every item you will NOT do, even if it seems obvious to you
- •Note any items that are 'subject to survey' where the price may change
- •Confirm whether Building Regulations notification is included or if you are handling it separately
Step 2: Calculate Your Materials Cost Accurately
Pull your materials list from the scope you have just written. For a standard combi boiler swap, you will typically need: the boiler unit itself, flue kit (standard horizontal or vertical extension kit if required), flue terminal, condensate trap and pipework, gas cock, flexible gas connector, pressure gauge, expansion vessel (on many combis this is internal, but check), new fill loop, system inhibitor, and a magnetic filter. If you are converting from regular to combi, add: new copper pipework to cap or remove the cylinder and F&E tank, and any additional copper runs to extend or re-route.
Do not use yesterday's prices. Copper and boiler prices have moved significantly over recent years and continue to fluctuate. Call your merchant or check your trade account online on the day you are pricing, not when you get back to the van. If you are buying the boiler on a promotion or getting a merchant discount, factor that in but do not assume the discount will still be there when you come to order. Build a 5 to 10 per cent materials contingency into your quote, especially on older properties where you may find unexpected corroded pipework once you start work.
One common pitfall is forgetting consumables: solder, flux, PTFE, clip screws, bracket fixings, silicone sealant for the flue penetration, and gas pipe clips. These seem trivial but on a full-day installation they can add up to £30 to £50, and if you forget them across ten jobs a month you are losing real money.
- •Price the boiler unit from your merchant account on the day of quoting
- •Include flue components, fittings, and system accessories separately
- •Add system inhibitor, magnetic filter, and fill loop if not already present
- •Do not forget consumables: solder, PTFE, silicone, clips, screws
- •Apply a 5-10% materials contingency for older or unknown installations
Step 3: Calculate Your Labour Cost
Be honest about how long the job will take you. A like-for-like combi swap in an accessible kitchen where the flue is going straight through the wall behind you is a one-day job for most experienced plumbers. A full system conversion, where you are removing a cylinder, draining an open-vented system, capping the feed-and-expansion tank, reconfiguring pipework, and commissioning from scratch, is typically a day and a half to two days minimum. If you underestimate the hours, you will either rush the job and miss something on commissioning, or you will absorb the loss yourself.
Set your daily or hourly rate based on your actual costs, not what you think the market will bear. Work out what you need to earn to cover your overheads (tools, van, insurance, Gas Safe registration, materials account, accountant, phone), then add your desired net income on top. As a rough benchmark in 2025, Gas Safe registered sole traders in England are typically charging between £280 and £450 per day depending on location, though London and the South East regularly exceed that. Do not use a day rate you pulled from a forum three years ago.
For a boiler installation, price labour as a fixed element tied to the scope, not an open-ended hourly rate. If the customer asks 'what if it takes longer?', that is your cue to explain that your quote covers the defined scope and that any additional works discovered (such as needing to upgrade the gas supply pipework) will be quoted separately before you proceed.
- •Be realistic about hours: do not price a 1.5-day job as a 1-day job
- •Base your day rate on your actual overheads, not market guesswork
- •Price labour as a fixed amount tied to a defined scope
- •Agree in writing how variations (extra works discovered on site) will be handled
Step 4: Account for Gas Safe Registration and Building Regulations Costs
Every boiler installation in the UK must be carried out by a Gas Safe registered engineer and must be notified to Building Control unless you are a member of a Competent Person Scheme. As a registered Gas Safe member, your registration with an approved Competent Person Scheme (such as APHC or NAPIT for plumbing) covers the Building Regulations notification and the Building Regulations compliance certificate for most boiler installations in England under Part L. However, this has a cost, typically around £30 to £60 per job depending on your scheme provider, and it needs to appear in your quote.
Do not absorb this cost into your general overhead and forget about it. On ten boiler installations a month, that is up to £600 in direct costs that needs to be recovered. Some tradesmen list it as a separate line item on the quote ('Building Regulations notification: £35'). Others build it into a fixed 'commissioning and certification' line. Either approach works, but it must be in the quote so the customer can see what they are paying for.
If you are working on a rental property, your obligations go further. The Gas Safety (Installation and Use) Regulations 1998 require the landlord to hold a valid Gas Safety Record (the CP12) within 12 months of your installation. That is the landlord's duty to arrange annually after you have completed the job, but you must commission the boiler correctly and issue your commissioning record at the point of handover. Build commissioning documentation time into your quote: it takes at least 30 minutes done properly.
- •Include the Building Regulations notification fee from your Competent Person Scheme
- •List commissioning and Gas Safe certification as a separate line on the quote
- •On rental properties, remind the landlord in writing of their CP12 obligations
- •Factor in at least 30 minutes for proper commissioning and documentation
Step 5: Add VAT (if Applicable) and Check the Reduced Rate
If you are VAT-registered, you need to apply the correct VAT rate to the job. Standard rate VAT on a boiler installation for a property that has been in use for more than two years is 5%, not 20%, under VAT Notice 708 (Energy Saving Materials and Heating Equipment). This reduced rate applies to the supply and installation of a boiler as a heating appliance in an existing residential property. This is a significant point that many sole-trader plumbers either miss entirely or get wrong, and HMRC will come after the difference.
The reduced rate covers the boiler, flue, controls, and reasonable associated materials when supplied as part of the installation. It does not cover pipework works that are clearly a building job rather than part of the boiler installation itself. If you are doing major pipework re-routing that is separable from the boiler fit, you may need to split the invoice and apply different rates to different lines. When in doubt, ask your accountant rather than guessing. Getting VAT wrong on ten jobs at, say, £4,000 per job is a very expensive mistake.
If you are not VAT-registered (below the £90,000 threshold as of 2025), none of this applies and you simply do not charge VAT. But if you are approaching that threshold, bear in mind that registering mid-year will require you to retrospectively account for VAT on previous sales over the threshold, so keep an eye on your turnover.
- •Residential boiler installations on properties over two years old: 5% VAT, not 20%
- •Reduced rate covers the boiler, flue, controls, and associated installation materials
- •Separable building works (major pipework re-routes) may attract 20% VAT
- •If not VAT-registered, confirm you are below the £90,000 threshold before the job starts
Step 6: Structure the Quote Document Correctly
A well-structured quote does three things: it tells the customer exactly what they are getting, it protects you legally if there is a dispute later, and it looks professional enough that the customer does not feel the need to get three more quotes from your competitors. You do not need a complicated multi-page document, but you do need specific elements in the right order.
Start with your business details: your name, trading name (if different), address, Gas Safe registration number, and contact details. Then include the customer's name and property address, and the date the quote was issued. A quote validity period is important: most tradesmen use 30 days, because materials prices and your availability can change beyond that. Next, list the works in clear sections as you scoped them in Step 1: what is included, what is excluded, and any provisional items. Include a payment terms section: how much is due on completion, whether you require a deposit, and how you want to be paid.
Under the Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013, if you are entering into a contract at a distance (for example, the customer accepted your emailed quote without meeting you in person to sign) or away from your business premises, the customer has the right to cancel within 14 days. You must make this clear in your quote or accompanying terms. In practice for boiler installations, most quotes are signed after a face-to-face survey, which means the cancellation right can be waived once work starts, but you must inform the customer of this in writing before they accept.
- •Your name, Gas Safe registration number, address, and contact details
- •Customer name, installation address, and quote date
- •Quote validity period (typically 30 days)
- •Detailed scope of works: inclusions, exclusions, and provisional items
- •Payment terms: deposit (if any), balance due on completion, accepted payment methods
- •14-day cancellation rights notice for distance or off-premises contracts
- •Space for customer signature and date of acceptance
Step 7: Present the Quote and Handle Objections
Do not email a quote and then go silent. Follow up within 48 hours to check the customer received it and to answer any questions. Most price objections at this stage are not actually about the total number. They are about the customer not understanding what they are paying for. If your quote is itemised properly, you can walk them through each line and explain why it is there. A customer who understands why the power flush is £200 is far less likely to argue about it than one who just sees a total figure.
If a customer comes back and says they have a cheaper quote, ask them what the other quote includes. Nine times out of ten, the cheaper quote is missing something: the Building Regulations notification fee, the magnetic filter, the power flush, or the correct boiler model. Do not drop your price to match an incomplete quote. Instead, explain what is in yours that is not in theirs. If the customer is still determined to go cheaper, let them go. A job where you have already compromised on price before you have started is never a pleasant one to be on.
One practical tip: send the quote as a PDF, not an editable Word document. A PDF cannot be tampered with after you have sent it, and it looks considerably more professional. If the customer needs to sign and return it, most PDF tools allow electronic signature, or you can ask them to reply by email with written confirmation, which is a valid form of contract acceptance in English law.
- •Follow up within 48 hours of sending the quote
- •Walk the customer through each line item if they query the price
- •Compare like-for-like if they have a cheaper competing quote
- •Send as a PDF, not an editable document
- •Get written acceptance before ordering materials or booking the job in
Step 8: Protect Yourself with Variation Clauses
Even the best survey cannot predict everything. On older properties especially, you will sometimes find corroded pipework, undersized gas supply pipes, or a flue route that simply cannot work in the way you planned. If your quote is entirely fixed and you have no variation clause, you absorb all of those surprises yourself. That is not sustainable on a tight margin job.
Include a short variation clause in your quote terms. Something along the lines of: 'This quote is based on the installation conditions observed during the survey on [date]. Should additional works be required as a result of conditions not visible at the time of survey (including but not limited to: gas supply pipework upgrades, additional flue components, or remediation of existing system defects), a variation will be agreed in writing before those works proceed.' This is not a blank cheque for you to add costs later; it is a fair protection for both sides.
The key phrase is 'agreed in writing before those works proceed'. If you discover a problem on site, stop, call the customer, explain the issue and the additional cost, get their written agreement (a reply-to-email or a message in your quoting app is sufficient), and then continue. Do not do extra work and then surprise them on the invoice. That is the fastest way to a dispute you are unlikely to win.
- •Include a variation clause in every quote for boiler work
- •Define what triggers a variation: conditions not visible at survey
- •Always agree variations in writing before carrying out the extra work
- •A WhatsApp or email reply from the customer is valid written agreement
Worked Example: Quoting a Combi Boiler Swap in a Three-Bed Semi
Here is a realistic worked example. The customer is Mrs Ahmed, who lives in a three-bedroom semi-detached house in the East Midlands. The existing boiler is a 14-year-old Potterton regular boiler in the kitchen, and she wants a like-for-like swap to a Worcester Bosch 4000 30kW combi, with the existing cylinder and F&E tank removed. The survey was carried out on 2 June 2025.
Materials breakdown: Worcester Bosch 4000 30kW combi (trade price from merchant) £820. Standard horizontal flue kit £55. Magnetic filter (Fernox TF1) £65. System inhibitor, sealant, and power flush chemicals £40. Copper fittings, PTFE, solder, and consumables £45. New gas cock and flexi connector £18. New room thermostat and programmer (Hive Active) £110. Condensate pipe run materials £22. Cylinder removal, capping materials £35. Total materials: £1,210.
Labour: Two days at a day rate of £320 per day. Total labour: £640. Building Regulations notification via Competent Person Scheme: £40. Commissioning and certification (including Gas Safe documentation): included in labour above. Quote subtotal before VAT: £1,890. VAT at 5% (reduced rate, residential installation, property over two years old): £94.50. Total quoted price: £1,984.50. Quote valid for 30 days from 2 June 2025. Payment terms: 30% deposit on acceptance (£595.35), balance on completion. This quote includes supply and installation of the above boiler and removal of the existing boiler, cylinder, and tank. It excludes any re-routing of existing radiator pipework, making good of walls or flooring, and any electrical consumer unit works. Should gas supply pipework need upgrading (to be determined on the day of installation), a written variation will be agreed before those works commence.
- •Boiler unit: £820 (trade price, Worcester Bosch 4000 30kW)
- •All materials and consumables: £390
- •Labour (2 days at £320/day): £640
- •Building Regulations notification: £40
- •Subtotal: £1,890
- •VAT at 5% (reduced residential rate): £94.50
- •Total: £1,984.50
- •Deposit on acceptance: £595.35 (30%)
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