The things that move the price most
- Whether the boiler stays where it is. A like-for-like swap in the same position is the cheapest job there is. Moving it means new gas, new flue, new condensate and often new pipework, and that is a substantially bigger piece of work.
- What type you are going to. Combi, system and regular boilers are different installs. Swapping from a regular boiler with a tank and cylinder to a combi means removing them and reworking the pipework, not just changing the appliance.
- The gas supply pipe. A lot of older properties were run in 15mm where a modern boiler needs 22mm. Upgrading that run can mean lifting floors, and it is one of the biggest hidden differences between quotes.
- The flue. Length, route, and whether it terminates somewhere that needs scaffolding or a roof kit.
- Cleaning the existing system. A chemical flush, or a full power flush on a dirty system, plus a magnetic filter. Most manufacturers require the system to be cleaned for the warranty to stand.
- Controls. A basic programmer, or a smart thermostat and thermostatic valves throughout.
- Making good. Boxing in, plastering, and taking the old cylinder or tank away.
What a complete quote should say
- The exact boiler make, model and output — not just "a new combi"
- The warranty length, and what you have to do to keep it valid (almost always an annual service by a registered engineer)
- Whether the system will be flushed, and how
- Whether a magnetic filter is included
- Whether the gas supply pipe needs upgrading, and if not, why not
- What controls are included
- Whether the old appliance, cylinder and tank are being removed
- That the installation will be notified under Building Regulations by a Gas Safe registered installer
Questions worth asking
Ask whether the gas run has been checked and measured, not assumed. Ask what happens if they lift the floor and find something. Ask who you ring if it fails in February, and whether that is the installer or the manufacturer.
An installer who has actually looked at your property will have clear answers to all three. One quoting from a phone call will not.
Getting comparable quotes
Get at least two, ideally three, and give each of them the same information — photographs of the current boiler, the flue outside and the position, plus your postcode. On PlumbGo you post the job once and local Gas Safe registered engineers come back to you, which at least means everyone is quoting the same job.
Be wary of any quote that is dramatically cheaper without explaining what it leaves out. Usually the difference is the flush, the filter, the gas run or the controls.
Common questions
Why are two quotes for the same boiler so different?
Usually because they are not quoting the same job. One may include a power flush, magnetic filter, gas pipe upgrade and new controls where the other is an appliance swap and nothing else. Compare the inclusions, not the totals.
Do I have to have an annual service?
For safety, it is strongly advisable. For your warranty, it is usually mandatory — most manufacturers void cover if you cannot show an annual service by a registered engineer.
Can I fit a boiler myself?
No. Work on gas appliances must be carried out by a Gas Safe registered engineer. It is a legal requirement, the installation has to be notified under Building Regulations, and doing it otherwise invalidates your insurance as well as being dangerous.
Related guides
What is actually included in a boiler service? Radiators cold at the bottom, hot at the top Landlord gas safety certificates: what you actually need
Find someone near you
Engineers set their own travel radius, so these pages show who genuinely covers each area.
Sunderland Newcastle Gateshead South Shields Washington Durham All areas