Combi, system, or regular?
Three types of boiler cover every UK home. The right one depends on how many people shower at once and how much space you have. Here's the quick-but-complete answer.
Combi boiler
A combi (combination) boiler heats your water on demand — no hot water cylinder, no cold water tank. Every tap runs straight off the mains. Around 70% of UK homes have one.
Best for: 1–2 bathroom homes, flats, or households of 1–4 people where only one shower runs at a time.
Pros: Compact (fits in a kitchen cupboard), endless hot water, no heat loss from a stored tank, lowest install cost.
Cons: Flow rate drops when two taps are on at once; not ideal for large households.
Typical cost: £1,800–£3,500 fitted.
System boiler
A system boiler works with a hot water cylinder but no cold water tank in the loft. Hot water is stored ready to deliver at full pressure to multiple taps simultaneously.
Best for: 2+ bathroom homes, 4+ person households, or anyone who wants two showers running at once without pressure drop.
Pros: Strong flow rate to multiple outlets, good with modern unvented cylinders, works with solar thermal and heat pumps.
Cons: Needs airing-cupboard space for the cylinder, stored hot water loses some heat over time.
Typical cost: £2,500–£4,500 fitted (more with a new cylinder).
Regular (heat-only) boiler
A regular boiler — sometimes called conventional or heat-only — uses both a hot water cylinder and a cold-water feed tank in the loft. Traditional UK setup, common in older homes.
Best for: Large older homes where the existing pipework is designed for it, or homes with poor mains pressure.
Pros: Handles poor mains pressure well, replaces like-for-like cheaply in period properties.
Cons: Two tanks to maintain, risk of loft tank leaks, less efficient overall system.
Typical cost: £2,200–£4,000 fitted.
Quick decision guide
- 1 bedroom flat, 1 shower: Combi.
- 2-bed semi, 1 bathroom, 2-4 people: Combi.
- 3-bed detached, 2 bathrooms, family: System (or powerful combi).
- 4+ bed with 2+ showers used simultaneously: System.
- Period property with gravity-fed pipework: Regular (or upgrade to system).
- Any home switching to heat pump later: System (compatible with hybrid setups).
Must-have boiler accessories
Whatever boiler you install, these accessories pay for themselves within 2 years:
- MagnaClean Professional 2 — magnetic filter that extends boiler life 5+ years. See our full filter comparison.
- Tado Smart Thermostat — 15-25% off heating bills via zoning. Full comparison in our smart thermostats roundup.
- Fernox F1 Protector — corrosion inhibitor (required by most warranties).
The brands worth buying
Worcester Bosch, Vaillant and Viessmann consistently top reliability surveys (Which?, Heating Hub). Ideal and Baxi sit in the mid-tier with lower prices but shorter warranties. Avoid older Potterton models where possible — efficiency has lagged the leaders.
Get fixed-price quotes
Tell us your home size, we'll route you to installers who'll spec the right boiler and quote a fixed price.
Get my free quotes