A system boiler is similar to a traditional boiler and are common in properties with more than one bathroom. In many cases they can be a good replacement for an older, traditional boiler.
They both store water in a cylinder tank which is then heated up and fed into the system to supply your taps/showers.
However, a system boiler is a closed system that only needs the boiler itself and the hot water cylinder.
While a traditional boiler will have a separate feed and expansion tank and cold-water storage tank in the loft. As such, a system boiler can save quite a bit of space.
It also has many of the external parts built into the unit, which can make installation quicker, easier and cheaper vs a conventional boiler.
For the reasons noted above, system boilers are usually preferable to traditional boilers. With the exceptions being in cases where your home is in a low water pressure area or you have an old radiator system which would not be compatible with one.
How does a system boiler work?
Cold water goes into the boiler directly from the mains. The boiler then heats the water and sends it to the hot water cylinder tank, where it is stored until needed.
When you turn on your tap/shower, water then comes from the hot water cylinder. Not from the boiler itself as is the case with a combi.
Because hot water is fed from a cylinder tank, it means you can run multiple hot taps/showers at the same time. Making this kind of boiler potentially a better choice for larger homes over a combi boiler.
Most system boilers will have programmable controls. This means you can schedule the cylinder to heat up in advance so you won’t have to wait for hot water.
Advantages of a System Boiler
- Easier install than traditional boiler: There are no water tanks in the loft and many components are built into the system.
- Great for homes with more than one bathroom: Because hot water come from a cylinder, a system boiler can supply 2 showers at the same time without loss of pressure or fluctuation in temperature.
- Takes less space than a traditional boiler: No cold-water storage tank or feed and expansion tank is needed in the loft. Especially important for those with limited space or without a loft.
- Built in components: Since many of the parts (pumps, valves etc) are built into the unit, they will be covered by the warranty from your boiler manufacturer. This also makes installation easier and cheaper.
- Works with solar: Since system boilers use a hot water cylinder this can be modified so the immersion heater receives power from your solar panels.
Disadvantages of a System Boiler
- Limited hot water supply: Because water comes from a hot water cylinder, once the tank is empty then you’ll have to wait for the tank to heat up again.
- Requires good incoming water pressure: System boilers don’t work well on low water pressure so you might be better with a traditional boiler if this is an issue in your area.
- Takes more space than a combi: While there is no need for tanks in the loft, a system boiler does still need a hot water cylinder (usually in the airing cupboard).
System Boiler Prices
There are lots of different system boilers on the market and range anywhere from around £500 all the way up to £3500 (excluding installation).