The Main Difference
Choosing between a combi and system boiler affects your hot water, space, and running costs. Here's what you need to know.
Combi Boiler
Heats water on demand - no storage tank needed
Best For:
- 1-2 bathroom homes
- Limited space
- Lower upfront cost
System Boiler
Stores hot water in a cylinder for later use
Best For:
- 3+ bathroom homes
- Multiple simultaneous taps
- High water demand
Detailed Comparison
| Feature | Combi Boiler | System Boiler |
|---|---|---|
| Hot Water | Instant, unlimited | Stored, can run out |
| Water Pressure | Mains pressure (strong) | Gravity or pump |
| Multiple Taps | Pressure drops | Handles well |
| Space Needed | Compact (kitchen cupboard) | Needs cylinder space |
| Installation Cost | £1,500 - £3,000 | £2,000 - £4,500 |
| Running Costs | Efficient, no heat loss | Some cylinder heat loss |
Which Suits Your Home?
Combi Boiler is usually best. Limited space, typically 1 bathroom, and you want instant hot water without storage.
Either works. Combi if 1-2 bathrooms. System if you have 2+ bathrooms used simultaneously or poor mains pressure.
System Boiler recommended. Multiple bathrooms, high simultaneous demand, and space for a cylinder.
Pros and Cons
Combi Pros
- Space-saving (no tank)
- Instant hot water
- Lower installation cost
- No heat loss from cylinder
- Great water pressure
Combi Cons
- Pressure drops with multiple taps
- Flow rate limited
- Poor with low mains pressure
- Not ideal for large homes
System Pros
- Multiple taps simultaneously
- Works with poor mains pressure
- Compatible with solar thermal
- Power showers possible
- Good for large families
System Cons
- Needs cylinder space
- Higher installation cost
- Can run out of hot water
- Some heat loss from cylinder
Cost Comparison
Combi Boiler Total
- Boiler: £800 - £2,000
- Installation: £500 - £1,000
- Total: £1,500 - £3,000
System Boiler Total
- Boiler: £1,000 - £2,500
- Cylinder: £300 - £800
- Installation: £800 - £1,500
- Total: £2,000 - £4,500
Quick Decision Guide
Choose Combi if:
- You have 1-2 bathrooms
- Good mains water pressure
- Limited space
- Budget is a priority
Choose System if:
- You have 3+ bathrooms
- Multiple people use hot water simultaneously
- Space for a cylinder
- Poor mains pressure