Two quotes for the 'same' boiler can land £1,000 apart, and that gap is rarely the boiler itself. It is almost always the labour, the parts around the boiler and the state of the pipework it is joining onto.
This guide splits a typical new boiler job into its real cost components, so you can read a quote line by line rather than just comparing the bottom number.
The four things you are actually paying for
Every boiler installation is really four separate costs bundled into one figure: the boiler unit itself, the labour to fit it, the system extras that protect it, and any building work needed to get pipework, gas and flue where they need to be.
A cheap quote that skips the extras is not a bargain, it is a boiler installed onto dirty water with no filtration, which tends to fail early.
- Boiler unit: the appliance itself, priced by output (kW) and brand tier
- Labour: removal of the old boiler, fitting, testing and commissioning
- System extras: magnetic filter, chemical flush, new thermostat, condensate pump if needed
- Building work: flue routing, gas pipe upsizing, cylinder removal or relocation
Swap, conversion or relocation, priced differently
A like-for-like swap, putting a new combi where the old combi was, is the simplest and cheapest job because the gas, flue, and pipework are already in the right place.
A conversion, such as changing a system boiler with a cylinder to a combi, or moving from an old back boiler, involves capping off pipework, removing a redundant cylinder and tanks, and rerouting the flue. This adds labour and materials.
A relocation, moving the boiler to a different room such as a loft or garage, adds pipe runs, possibly a condensate pump if it cannot drain by gravity, and more flue length. It is the most expensive option but sometimes the only sensible one in a small kitchen.
Indicative cost ranges
| Job type | Indicative range | What drives the top end |
|---|---|---|
| Like-for-like combi swap | £2,200 to £3,500 | Premium brand, higher kW output |
| System to combi conversion | £2,800 to £4,500 | Cylinder removal, extra capping off |
| Boiler relocation | £3,200 to £5,500 | New flue run, condensate pump, longer pipe runs |
| Gas pipe upsizing | £150 to £600 | Length of run, number of fittings, wall chasing |
| Unvented cylinder addition | £1,200 to £2,200 | Cylinder size, kitchen or loft access |
Why older Borders stone properties often cost more
A lot of the housing stock across Kelso and the wider Borders is solid stone with narrow void spaces, timber suspended floors and gas meters set well away from where the boiler needs to sit. That geography adds real cost that has nothing to do with the boiler brand.
Common extras we price in on these properties include longer gas pipe runs from an external meter box, flue terminations that need to clear a neighbouring window under Building Standards guidance, and additional pipe insulation where runs pass through unheated lofts or cold voids.
Thick stone walls can also mean the flue core drill takes longer and sometimes needs a longer flue kit than a standard new-build fitting would, which is worth asking about at quote stage.
Reading a quote so you compare like for like
Ask each installer to itemise the boiler model and kW output, whether a magnetic filter and power flush are included, what warranty length applies and whether it is registered on installation, and whether gas pipe or flue work has been allowed for.
A quote that is silent on filtration and flushing is not automatically wrong, but it means those costs may appear later, either as an add-on or as an early breakdown that is not covered under warranty.
Frequently asked questions
- Is the cheapest quote ever the right choice?
- Sometimes, but only if it includes the same scope as the other quotes. Compare the boiler output, filter, flush and warranty registration before comparing price.
- Does moving the boiler always cost a lot more?
- It usually adds cost because of extra pipe, flue and possibly a condensate pump, but the amount depends on how far it is moving and whether a gravity drain for condensate is available at the new location.
- Why do some quotes include a cylinder and others do not?
- It depends on your hot water demand and current setup. A single-bathroom combi household needs no cylinder, while a larger household moving to an unvented cylinder for better pressure will see that added as a separate cost line.
- Will an older property always cost more to fit?
- Not always, but solid stone walls, longer pipe runs to the meter, and flue clearance rules mean it is worth having a site survey rather than a phone quote for these properties.
Want a quote that is actually comparable?
We survey the property first, so your quote reflects the real job, not a generic like-for-like price.