If your home currently has a regular boiler, you may be wondering whether replacing it with another regular boiler is the best option — or whether it’s time to switch to a combi.
A regular boiler, also known as a conventional or heat-only boiler, works with a hot water cylinder and usually cold-water storage tanks.
A combi boiler combines heating and hot water into a single appliance and doesn’t need a separate hot water cylinder.
For some homes, switching to a combi can free up valuable space and simplify the heating system. For others, keeping a regular boiler may provide better hot water performance.
A regular boiler heats water for your radiators and hot water cylinder.
The system normally includes:
The cold-water storage tanks are often located in the loft.
This type of system has been used in UK homes for many years and can be particularly useful where mains water pressure is low.
A combi boiler provides central heating and hot water directly from one appliance.
It doesn’t require a hot water cylinder or loft storage tanks.
When you turn on a hot tap, the boiler heats the incoming mains water.
This makes a combi a compact solution and means there is no stored tank of hot water that can run out.
| Feature | Regular boiler | Combi boiler |
|---|---|---|
| Hot water cylinder | Yes | No |
| Loft storage tanks | Usually | No |
| Hot water | Stored | On demand |
| Space required | More | Less |
| Low mains pressure | Can be suitable | May be suitable |
| Multiple simultaneous outlets | Good with suitable cylinder | More limited |
| Hot water storage losses | Yes | No |
| System conversion | Existing arrangeents | Requires changes |
There isn’t a universal answer.
A combi could be a good choice if:
However, staying with a regular boiler may make more sense if:
This is more involved than simply taking one boiler off the wall and putting another in its place.
A typical conversion can involve:
Because of this extra work, a regular-to-combi conversion generally costs more than a like-for-like boiler replacement. Current published cost guides put many conventional-to-combi conversions around £3,000–£4,500, although the actual price depends heavily on the property.
Not automatically.
A combi relies on the incoming mains water supply.
If the incoming mains supply has poor flow or pressure, installing a combi won’t magically increase it.
This is one of the most important checks an installer should make before recommending a combi conversion.
Keeping the replacement boiler in the same position can reduce installation time and the amount of new pipework required.
Moving the boiler means additional work involving pipework, the flue, condensate drainage and potentially electrics.
Modern condensing boilers are designed to operate efficiently, regardless of whether the system is a combi, system or regular arrangement.
The bigger question is whether the system is appropriate for your household.
A smaller home with modest hot water demand may benefit from the simplicity of a combi. A larger home may benefit from storing hot water in a cylinder.
Replacing the boiler can be a good opportunity to review your controls.
Modern heating controls can include programmers, room thermostats, smart thermostats and thermostatic radiator valves. Good controls allow the heating system to operate only when and where heat is needed.
It can be.
The main benefits are:
The potential disadvantages include:
The short answer
A regular boiler doesn’t necessarily need to be replaced with a combi.
If you have good mains water pressure, modest hot water demand and want to reclaim space, a combi conversion may make sense.
If you have multiple bathrooms or high hot water demand, keeping a regular system or changing to a system boiler may be a better option.
The right choice should be based on your home, not simply on the age of your boiler.
Yes. A regular boiler system can usually be converted to a combi, although the hot water cylinder, tanks and some pipework may need to be removed or altered.
A typical conversion can cost around £3,000–£4,500, but the actual price depends on the boiler, property and amount of pipework required.
A combi may not be suitable if your incoming mains water pressure or flow is poor. Your installer should check both before recommending one.
Potentially. Removing the hot water cylinder and loft storage tanks can create useful additional storage space.
Often, yes. A combi can be a practical choice where space is limited and hot water demand isn’t particularly high.
Both use a hot water cylinder. A regular boiler generally also needs cold-water storage and feed-and-expansion tanks, whereas many of the components of a system boiler are built into the appliance.
