The short answer
A like-for-like combi swap in Birmingham starts at £1,999 fitted and runs to £2,899 for a Worcester Greenstar 8000. Converting an older cylinder or open-vent system to a combi starts at £2,699. Those are fitted figures, not boiler-only figures.
| Job | Warranty | Fitted price |
|---|---|---|
| Baxi / Main Eco Compact — combi swap | 5 yr | £1,999 |
| Worcester Greenstar 1000 — combi swap | 5 yr | £1,999 |
| Baxi 600 — combi swap | 7 yr | £2,199 |
| Worcester Greenstar 4000 — combi swap | 10 yr | £2,699 |
| Vaillant ecoTEC plus — combi swap | 10 yr | £2,699 |
| Worcester Greenstar 8000 — combi swap | 10 yr | £2,899 |
| Conversion to combi (from system or open vent) | — | from £2,699 |
Every price includes the boiler, horizontal flue, wireless thermostat, magnetic filter, system cleanse and inhibitor, Building Regulations notification, and removal of the old boiler. Same-position swaps. Estimates confirmed after a free survey.
What the fitted price includes
A meaningful boiler price is the complete job: the appliance, a horizontal flue, a wireless room thermostat, a magnetic system filter, chemical cleanse and inhibitor, all fittings, the Building Regulations notification, and the manufacturer warranty registered in your name. If a quote you are comparing is much cheaper, check which of those it quietly leaves out.
What can add to it
We would rather flag these now than surprise you on the day. A gas supply pipe that is undersized for the new boiler's output, a flue that has to be re-routed, a fused spur that needs moving, a system so heavily sludged it needs a power flush before the warranty is valid, or condensate that has to be run to a soil stack — any of these add cost. A free survey catches all of them before you commit.
Swap versus conversion
The single biggest driver of price is not the brand — it is whether your new boiler goes where the old one was. A same-position swap reuses most of the pipework and is a one-day job. A conversion removes a cylinder and tanks and re-runs pipework, which is why it starts higher, at £2,699, and takes two days.