Two quotes for the same property can differ by thousands and both be honest. The gap is almost never the boiler itself — it is what the installation includes. A straight swap in the same position with existing pipework reused is a different job from relocating an appliance, converting a system type, upgrading the gas run and cleaning a twenty-year-old heating circuit.
This page explains the line items so you can compare quotes on the same basis rather than on headline price.
The five things that move the price most
- Straight swap vs conversion: moving from a cylinder system to a combi, or vice versa, adds pipework, controls and often a cylinder removal.
- Position: relocating the boiler means new flue, gas, condensate and heating connections, plus making good.
- Gas supply: an undersized existing gas run has to be upgraded to meet the new appliance's demand.
- Flue route: a simple horizontal flue is cheap; a vertical flue, a long run or a listed-building elevation is not.
- System condition: a heavily sludged system needs a power flush and filter before a manufacturer will honour a warranty.
Indicative ranges for this area
As a guide only, a like-for-like combi replacement in a straightforward property typically sits in the low thousands; system conversions, relocations and larger properties push meaningfully higher. Oil boiler replacements and LPG work carry their own cost profile because of tank, supply and siting factors.
We do not publish a fixed figure because a genuine price depends on the gas run, flue route and system condition — and any installer quoting confidently without seeing those is guessing.
What should always be in the quote
- The exact appliance model, output in kW, and the warranty length in writing.
- Whether a system clean or power flush is included, and which type.
- A magnetic filter and correct inhibitor dosing.
- Controls: what thermostat or smart control is fitted, and whether the system is zoned.
- Gas Safe registration, Building Standards notification and warranty registration.
- Making good, waste removal and the old appliance's disposal.
Where spending more genuinely pays back
Correct sizing, a longer manufacturer warranty and proper controls are the three places extra money reliably returns. An oversized boiler cycles, wastes fuel and wears faster. A twelve-year warranty on a well-supported brand removes a decade of repair risk. Good controls with zoning cut runtime in houses that are not occupied evenly all day — which describes most rural Borders properties.
Frequently asked questions
- Why does one quote include a power flush and another does not?
- Because one installer has assessed the system condition and the other has not, or has priced a chemical clean instead. On an old system, skipping this risks the new appliance and the warranty. Ask which is included and why.
- Is a bigger boiler better?
- No. Output should match heat loss and hot water demand. An oversized appliance short-cycles, which reduces efficiency and increases wear. A correct heat loss calculation should sit behind the recommendation.
- Does a longer warranty cost much more?
- The extended warranty itself is typically modest, but it is usually conditional on accredited installation and annual servicing. As a Vaillant Advanced Installer we can offer extended warranty terms that a non-accredited installer cannot.
- Do you charge for a quotation visit?
- No. We survey, calculate the heat loss and provide a written quote with the specification set out line by line.
Get a boiler quote that shows the whole job
Send your postcode, current boiler make and whether you have a hot water cylinder, and we will arrange a survey.