How to Compare Boiler Quotes Without Getting Caught Out

Updated July 2026 · Emergency Plumber Chelsea

Start with the same boiler. A quote is only comparable if it names the exact boiler: the manufacturer, the model and the output in kilowatts. A quote that says "combi boiler, supply and fit" tells you almost nothing, because a budget model and a premium one can differ a great deal in build quality, warranty and price. If one installer recommends a bigger or smaller output than another, ask why. Our guide on what size boiler you need explains how output should be matched to your hot water demand and the size of the property, not simply to the old boiler.

What a good boiler quote should list. Expect a written, itemised quote that covers the boiler and its output, the flue and any flue extension or relocation, the heating controls, a system clean or flush and a magnetic filter, any gas pipe upgrade, the condensate pipe route, removal and disposal of the old boiler and any tanks, commissioning, notification under Building Regulations and registration of the manufacturer warranty. It should also say how long the job will take, what is excluded, and how and when you pay. If any of these items are missing, ask whether they are included before you compare prices.

Why boiler quotes differ so much. The same boiler can be quoted at very different prices because the work around it varies from home to home. A like-for-like swap in the same position with a flue that meets current rules is the simple end. Costs rise when the boiler moves, when the flue has to be rerouted, when the gas supply pipe is too small for a modern combi, when the condensate pipe has no easy route to a drain, when the system needs a thorough clean, or when an old tank-fed system is being converted. A quote that seems cheap may simply leave these things out, and a quote that seems high may be the only one that has priced them in.

Survey or online quote? Online fixed-price quotes built from a few photos are convenient, and for a straightforward swap they can be accurate. The risk is the job that turns out not to be straightforward, where extras are added on the day. A survey in person lets the installer check the flue position, gas pipe size, condensate route, pressure and flow at the taps, and access to the boiler location. For anything other than a simple like-for-like swap, a survey-based quote is usually the safer basis for comparison.

The system clean and filter. Most manufacturers expect the heating system to be cleaned when a new boiler goes in, and a magnetic filter is commonly fitted to catch sludge before it reaches the new heat exchanger. Many make the warranty conditional on this work being done and recorded. If one quote includes a power flush or chemical clean and another does not, the gap in price is partly explained. Our guide to power flush costs explains when a full power flush is needed and when a lighter clean will do.

Heating controls count too. When a boiler is replaced in England, the Building Regulations require suitable time and temperature controls, and a replacement combi boiler also needs an extra energy-saving measure such as a smart thermostat with automation and optimisation, weather compensation or load compensation. A quote that includes a basic dial thermostat and one that includes a smart control are not pricing the same thing. Check which control each installer is proposing and whether it meets the rules.

Check the engineer, not just the price. Anyone installing a gas boiler must be on the Gas Safe Register. Ask for the engineer's registration number and check it on the Gas Safe Register website, including that they are qualified for the work you need. A registered installer notifies the local authority through the Gas Safe scheme, and you should then receive a Building Regulations compliance certificate. Our guide on how to check a plumber is legitimate covers the wider checks worth making before you let anyone start.

Warranty terms are part of the price. Manufacturer warranties vary by model and often depend on the boiler being registered soon after installation, the system being cleaned and the boiler being serviced every year. Some longer warranties are only available through installers approved by that manufacturer. When comparing quotes, note the warranty length each one offers, who registers it, and what you must do to keep it valid. A slightly higher price with a longer, properly registered warranty can be the better deal.

Red flags in a boiler quote. Be wary of pressure to sign on the day, discounts that expire within hours, a large deposit taken before any materials are ordered, a quote that will not name the boiler model, a price given without anyone looking at the flue or gas pipe, or an offer of a lower price for cash with no paperwork. Get everything in writing. Our guide to consumer rights and payment protection explains your position if work is done badly or not finished.

Chelsea homes: points to raise with every installer. In a mansion block, the flue position may be restricted by the lease or the building, and the freeholder or managing agent may need to approve any change, so ask each installer to confirm the flue route before you commit. In a conservation area, a new flue on a front elevation can raise planning questions; see our guide to boiler flues in conservation areas. In period houses, older pipework, tanks in the loft and long pipe runs up several floors all affect what the job involves. Parking and access on residential streets can also add time on the day, and a good quote will allow for it.

How many quotes to get. Three quotes is a sensible number for most boiler replacements. Fewer gives you little to compare, while many more tends to muddy the picture. Give each installer the same information: the rooms and bathrooms in the home, how many people live there, whether you want to keep the boiler in the same place, and whether you are keeping or removing a hot water cylinder. If the quotes still differ widely, ask each installer to explain the difference. For a guide to typical budgets, see how much a new boiler costs, and for the time the work takes, see how long it takes to replace a boiler.

Should you be getting quotes at all? If your boiler is only a few years old and one part has failed, a repair may be better value than a replacement. If it is older, breaking down often, or parts are no longer made, replacement usually makes more sense. Our guide on when to replace your boiler will help you decide before you start collecting quotes.

Getting a boiler quote in Chelsea. Call Emergency Plumber Chelsea on 020 3002 6667 to arrange a visit. We look at the boiler position, flue, gas supply, condensate route and your hot water needs, then give you a clear, itemised price before any work starts. A boiler replacement runs well over three hours, and there is no call-out fee on jobs over 3 hours. See our boiler installation service for replacements and our boiler repair service if you would like the old boiler checked first. We cover SW3, SW10, Knightsbridge, Sloane Square, South Kensington and Fulham.

Quick tips

• Ask every installer to name the exact boiler make, model and output in writing.
• Check each quote covers the flue, controls, system clean, filter, gas pipe and condensate work.
• Look up the engineer's Gas Safe registration number before agreeing to anything.
• Note the warranty length, who registers it and whether annual servicing is required to keep it.
• In a mansion flat, confirm the flue route with your managing agent before accepting a quote.

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