A heat-only boiler costs roughly £500–£1,000 less than a like-for-like combi installation, but adds £800–£2,000 in cylinder and tank hardware.
If your home has a traditional hot water cylinder and you are replacing a heat-only (regular or system) boiler, you may save on the boiler unit itself but face extra costs for the separate storage tank. Heat-only boilers heat water in a cylinder, storing it for later use, whereas combi boilers heat water on demand without a cylinder.
According to Checkatrade and Boiler Guide 2026 pricing surveys, the typical total installed cost for a heat-only boiler ranges from £1,800 to £3,500, compared with £2,500 to £4,500 for a combi boiler (Checkatrade, 2026; Boiler Guide, 2026). The Energy Saving Trust notes that the extra cylinder and tank hardware typically adds £800–£2,000 to a heat-only system (Energy Saving Trust, 2026).
Heat-only boiler prices range from £600 to £1,400 for the unit alone, depending on output and brand.
The unit price of a heat-only boiler varies with its heat output (measured in kilowatts, kW) and manufacturer. Lower-output models for small homes cost less, while high-output models for larger properties command a premium.
- Entry-level 12–18 kW units: £600–£900 (e.g., Baxi 600, Worcester Greenstar Ri).
- Mid-range 18–24 kW units: £800–£1,200.
- Premium 24–30 kW units: £1,000–£1,400 (e.g., Vaillant ecoTEC plus, Ideal Logic+).
These figures are based on manufacturer RRP lists from Baxi, Worcester, Vaillant, and Ideal for 2026, as well as the MCS product database (MCS, 2026).
Installation labour adds £800–£2,000, with higher costs for cylinder and tank fit.
Labour costs depend on the complexity of the job. A simple swap of an existing heat-only boiler in the same location is cheapest, while a full system with a new unvented cylinder and expansion tank costs more.
- Basic swap (boiler only, same location): £800–£1,200.
- Full system including unvented cylinder and expansion tank: £1,500–£2,000.
- Additional costs: flue repositioning (£200–£400), gas pipe upgrade (£150–£300), system flush (£100–£200).
Data from the Gas Safe Register 2026 average installation cost survey and the Energy Saving Trust guide to boiler installation confirm these ranges (Gas Safe Register, 2026; Energy Saving Trust, 2026).
A heat-only system typically costs £1,500–£2,500 more than a combi over 10 years due to cylinder losses.
Heat-only systems lose 1–2 kWh/day through cylinder standing losses, heat escaping from stored hot water. Combi boilers have no standing losses because they heat water on demand, but they have lower flow rates for multiple taps simultaneously.
The Energy Saving Trust estimates that the annual extra gas cost for a heat-only system in a typical 3-bedroom home is £50–£100 (Energy Saving Trust, 2026). Over 10 years, this adds up to £500–£1,000 in fuel costs. Combined with the higher initial hardware cost (£800–£2,000), the total extra cost is roughly £1,500–£2,500 compared with a combi system, as per DESNZ energy consumption tables (DESNZ, 2026).
Quick numbers, typical heat-only boiler costs at a glance
| Boiler type | Unit price (excl. VAT) | Installation labour (basic swap) | Installation labour (full system with cylinder) | Total installed cost (low) | Total installed cost (high) | Annual gas cost (3-bed home) |
|---|---|---|---|---|---|---|
| 12 kW | £600 | £800 | £1,500 | £1,400 | £2,100 | £50–£100 |
| 18 kW | £800 | £900 | £1,600 | £1,700 | £2,400 | £50–£100 |
| 24 kW | £1,000 | £1,000 | £1,800 | £2,000 | £2,800 | £50–£100 |
| 30 kW | £1,200 | £1,200 | £2,000 | £2,400 | £3,200 | £50–£100 |
Data sources: MCS register, Gas Safe Register, and Energy Saving Trust 2026 (MCS, 2026; Gas Safe Register, 2026; Energy Saving Trust, 2026).
The cheapest heat-only boiler option in 2026 is a 12 kW unit with a basic swap, totalling roughly £1,400–£1,600 installed.
A 12 kW heat-only boiler is the smallest common size, suitable for a 1–2 bedroom home with low hot water demand. A basic swap assumes your existing cylinder and pipework are compatible with the new boiler, so no major system changes are needed.
The typical breakdown is £600 for the boiler unit plus £800–£1,000 for labour, giving a total of £1,400–£1,600. This is based on Checkatrade 2026 data and Gas Safe Register installer quotes (Checkatrade, 2026; Gas Safe Register, 2026).
To qualify for a heat-only boiler installation, the installer must be Gas Safe registered and the system must meet Building Regulations Part L.
Gas Safe Register registration is a legal requirement for any gas boiler work in the UK. If your system includes an unvented hot water cylinder, the installer must also hold a G3 unvented hot water storage certificate (GOV.UK, 2026).
The system must comply with Building Regulations Part L, which requires a boiler efficiency of at least 92% ErP, a smart thermostat, and zone controls for heating (GOV.UK, 2026). DESNZ boiler efficiency standards also apply (DESNZ, 2026).
Compare heat-only vs combi boiler costs Guide to hot water cylinder installation costs
Frequently Asked Questions
A heat-only boiler costs £1,800–£3,500 installed, according to Checkatrade and Boiler Guide 2026 pricing surveys. The unit alone ranges from £600 to £1,400, with cylinder and tank hardware adding £800–£2,000.
Yes, a heat-only boiler is typically £500–£1,000 cheaper than a like-for-like combi installation. However, the extra cylinder and tank hardware adds £800–£2,000, so total costs may be similar.
Installation labour for a heat-only boiler costs £800–£2,000, according to the Energy Saving Trust. A basic swap in the same location is cheapest, while a full system with a new unvented cylinder costs more.
Entry-level heat-only boilers from Baxi and Worcester cost £600–£900 for 12–18 kW models. Premium brands like Vaillant and Ideal cost £1,000–£1,400 for 24–30 kW units, based on 2026 manufacturer RRP lists and the MCS product database.
Yes, a heat-only boiler requires a separate hot water cylinder and usually an expansion tank. The Energy Saving Trust notes that cylinder and tank hardware typically adds £800–£2,000 to the total installation cost.
