Installations vary in length far more than people expect. A straight swap in a good position can be a single day. A conversion from a cylinder system, or a relocation from an upstairs cupboard to a kitchen, is comfortably two to three days, mostly spent on pipework rather than on the appliance.
What should not vary is the sequence, or the paperwork you hold at the end. Here is the whole thing, stage by stage.
Stage by stage
- 1
Survey, before any quote
Mains flow and pressure measured, gas supply pipe sized, flue route and terminal position checked, system water condition assessed, electrics and controls reviewed.
- 2
Protecting the house
Dust sheets, floor protection on the route in and out, and a plan for where the old appliance and packaging go.
- 3
Isolation and drain down
Gas, water and electrical supplies isolated and proved dead, then the system drained at the lowest point.
- 4
Removal
Old appliance disconnected and taken out, along with the old flue. On conversions, cylinder and loft tanks are removed and redundant feeds capped.
- 5
Pipework and gas
New primaries run, gas supply upsized where the survey required it, condensate routed to a frost-safe termination, filter position prepared on the return.
- 6
Hanging and flue
Boiler mounted level and secure, flue assembled to the manufacturer's kit and sealed, terminal clearances confirmed against the position rules.
- 7
Flushing and dosing
System cleansed to remove debris, then refilled and dosed with corrosion inhibitor. On a dirty system this is where a power flush belongs.
- 8
Commissioning
Gas rate checked, combustion analysed against the data plate, pressures set, controls configured, and every radiator brought up and balanced.
- 9
Handover
Operation demonstrated, controls explained, and the documentation handed over rather than posted later.
The paperwork you should end up holding
If any of these is missing, ask for it before the job is closed.
- Building Regulations compliance notification for the installation
- Benchmark or equivalent commissioning record, completed and signed
- Gas Safe registered engineer details for the work carried out
- Manufacturer warranty registration confirmation for the appliance
- Inhibitor dosing record and details of the filter fitted
- Manuals for the boiler and any new controls
Where installations most often go wrong
The two failures we see most in other people's work are skipped system cleaning and unsized gas supply. Both are invisible on the day and both cause problems later: the first fouls a brand-new heat exchanger, the second means the appliance can never reach its rated output without dropping the gas pressure outside limits.
A third is controls left as they were. Fitting a modulating condensing boiler and leaving it slaved to an old on-off cylinder thermostat wastes much of the efficiency you have just paid for.
Book a boiler installation survey
Every quote we issue follows a survey of the gas run, flue route, mains flow and system condition — so the sequence above is planned before anyone arrives with a boiler.
You can judge an installation without knowing a thing about gas: was there a survey, was the system cleaned, was the boiler commissioned with a meter rather than by eye, and did the paperwork arrive. Four questions, and they filter out most bad jobs.