What affects the cost
Cost depends on the type of system (combi vs system vs conventional), whether it's a straightforward swap or a full system change, boiler brand and output size, and property access. Moving a boiler's location, rather than replacing it in place, adds cost because of the extra pipework, flue routing and making good involved.
What a good heating quote should include
A proper quote should specify the boiler make and model (not just "a combi boiler"), whether a powerflush is included, the warranty length, and what certificate you'll receive on completion. If a quote is missing the boiler model, ask before agreeing.
What size boiler do you actually need?
An oversized boiler costs more to buy and can run less efficiently; an undersized one struggles with demand, particularly hot water for multiple bathrooms. Sizing should be based on a heat loss calculation for the property and how many bathrooms/hot water outlets are used at once, not just the previous boiler's output copied across.
Common heating engineer jobs
Heating engineers install, service and repair boilers and central heating systems: annual boiler services, fault diagnosis, radiator installation and balancing, powerflushing, and full system replacements. Many also work on unvented hot water cylinders and, increasingly, heat pumps and other low-carbon heating.
Why Gas Safe registration is a legal requirement
Anyone installing, servicing or repairing a gas appliance or gas pipework in the UK must by law be on the Gas Safe Register, which replaced CORGI in 2009. This covers boilers, gas fires and gas cookers. Using an unregistered engineer for gas work isn't just risky, it's illegal, and any resulting certificate isn't valid.
Boiler cover and service plans
Separate from a manufacturer's warranty, some homeowners take out an annual boiler cover plan (often through an energy supplier) that includes servicing and breakdown cover. Worth checking what's already included in a recent warranty before paying for overlapping cover.
Oil-fired boilers, what's different
Oil boilers are common in properties off the mains gas network, need an oil storage tank with its own maintenance and safety considerations, and are serviced by OFTEC-registered engineers rather than Gas Safe (which only covers gas). If you're off-grid, confirm your engineer's OFTEC registration specifically.
Why an annual boiler service matters
An annual service checks for gas leaks, correct combustion, and general safety, and most manufacturer warranties require it to stay valid. It's also when a heating engineer is most likely to catch a developing fault — a failing part or a a pressure issue — before it causes a breakdown, particularly in winter when boilers are used hardest.