UK 2026 / May 2026
Boiler replacement cost by type
Four UK domestic boiler types. Cheapest path is almost always a like-for-like swap on whatever you have today; switching type adds GBP 500-GBP 2,000 of pipework and decommission cost. Sizing for the right kW output is just as load-bearing as picking the type.
Side-by-side comparison
| Type | Installed cost | Install time | Typical kW | Best for |
|---|---|---|---|---|
| Combi | GBP 1,800 - GBP 3,500 | 1 day | 24-32 kW | 1-3 bed homes with one bathroom and decent mains pressure |
| System | GBP 2,000 - GBP 4,000 | 1-2 days | 18-30 kW | 3-5 bed homes, 2+ bathrooms, hot water demand running multiple taps simultaneously |
| Regular (heat-only) | GBP 2,000 - GBP 4,500 | 1-2 days | 12-30 kW | Older homes with existing loft tank, large homes where the system already works well |
| Back boiler conversion | GBP 2,500 - GBP 5,000 | 2-3 days | 24-32 kW combi target | 1960s-1980s houses with a back boiler behind the gas fire that has stopped working |
The four types in detail
Combi
GBP 1,800 - GBP 3,500Heats water on demand from the mains. No hot water cylinder or loft tank needed. The default choice for most 1-3 bedroom UK homes; 70% of UK boiler sales (Energy Saving Trust).
Pros
- Compact (fits in a kitchen cupboard)
- No tank, no cylinder, no airing-cupboard real estate lost
- Instant hot water
Cons
- Struggles with two showers running at once
- Output limited by mains pressure
- Not ideal for 4+ bed homes
System
GBP 2,000 - GBP 4,000Heats a hot water cylinder which then feeds multiple taps. No cold water tank in the loft (the mains feeds the boiler directly). The sweet spot for 3+ bed homes with multiple bathrooms.
Pros
- Strong flow to multiple taps
- No loft cold tank needed
- Compatible with solar thermal
Cons
- Hot water cylinder takes space (typically an airing cupboard)
- Tank can run out on extended demand
- Higher install cost than combi
Regular (heat-only)
GBP 2,000 - GBP 4,500The traditional UK setup. Boiler + hot water cylinder + cold water tank in the loft. Found in older homes (pre-1990s). Usually replaced like-for-like to avoid major pipework changes.
Pros
- Works with existing pipework
- Excellent for high-demand homes with multiple bathrooms
- Loft tank gives gravity feed reliability
Cons
- Requires loft cold tank space
- Most components to maintain
- Higher total cost vs combi when converting
Back boiler conversion
GBP 2,500 - GBP 5,000Replacing a back boiler (the unit behind a 1960s-1980s gas fire) almost always means converting to a wall-mounted combi. Highest-cost replacement path because of the decommission, pipework rerouting, and new flue work.
Pros
- Frees up the chimney breast / fire surround
- Reclaims hot-water cylinder space
- Modern combi is 30-40 percentage points more efficient
Cons
- Most disruptive replacement
- Old back boiler must be decommissioned by Gas Safe engineer
- New flue must be cut through external wall (Part J distance rules apply)
Still deciding whether to replace at all? Start with repair or replace? or 8 signs you need a new boiler. Considering low-carbon? See gas boiler vs heat pump cost.