This type of boiler produces instantaneous hot water and works directly off the incoming water main.
They are self contained so there are no other water storage tanks in the property.
They contain all the main components otherwise found elsewhere on the system such as the heat exchanger and the expansion vessel.
As a result over 80% of new installations in the uk today are of the combination type.
Combis are easier to install & maintain.
They are widely recognised as being cheaper to run and maintain than the storage type.
If you have a property but with more than one bathroom it’s best to choose a larger output.
This is done automatically in our pricing tool.
- Lower running costs – there is no waste associated with keeping a hot water cylinder full when you may not need it.
- Space saving – you can remove your old tanks creating space for storage and other purposes.
- Service and maintenance costs can be reduced if you buy a boiler with an extended manufacturer warranty as key system components are mostly covered.
- Hot water on demand – get your hot water exactly when and where you need it just by opening the tap.
- Poor incoming water pressure or flow rates affect the hot water delivery performance.
- Without a hot water cylinder there is no hot water back up provided by an immersion heater.
- Hot water delivery to the taps can be affected when two or more users are trying to draw hot water at the same time.
System Boilers are similar to Combi’s and they are ‘closed system’ meaning they work in tandem with a pressurised storage cylinder.
This type of boiler incorporates many of the same components as Combi’s
They do still still rely on water storage tanks to supply the heating system and hot water taps.
These are generally situated elsewhere in the central heating system.
There are no tanks in the loft which with regular boilers are used to supply the heating system with water.
The heating pump and expansion vessel are normally incorporated within the boiler case.
They are often installed to work alongside unvented hot water cylinders.This type of boiler
- Better for properties with a high hot water demand where there is a need to service 2 or more hot taps at the same time
- Like combis the majority of system components are inside the boiler case meaning the boiler warranty gives greater protection.
- This type can be a benefit in flats where there is no room for storage tanks above the boiler.
- This product relies on good incoming water flow rates to be effective.
- More space is required to site your boiler and cylinder. This is worth remembering if you want to change from a combi boiler.
Expansion occurring as the heating system water temperature rises is catered for within the boiler by the expansion vessel.
The user will be required to ensure the system pressure is topped up via the filling loop.
This is similar to how a combi works.
A separate hot water cylinder will be required to feed the heating circuits and hot water taps.
This will almost certainly be of the unvented type.
This avoids the need for feed and expansion tanks above the boiler.
Regular or ‘heat only’ boilers work in harness with a storage cylinder
They provide heating and hot water.
Utilise traditional British design and are found in many hundreds of thousands of properties.
This type is often replaced by a combi when house type, number of bathrooms and flow rate considerations have been made by your installer.
There is no reason why a regular type can’t be replaced by another one
This could turn out to be the best option in your circumstance.
It’s possible your boiler is situated behind a gas fire in the living area. This is called a fire and back boiler unit (BBU).
If you have a BBU you will need to upgrade to another type.
BBU’s are now unavailable.
- Less reliant on acceptable incoming water flow rates as they are designed to work on low pressure.
- Less expensive to buy than other types as there are less system components within the case.
- Likely to work better on older ‘open-vented’ system due to low internal system pressures.
- Immersion heater back up ensures hot water is available in the event of a breakdown.
- More important system components are external to the case and will not be covered by the warranty.
- Slower heat up than sealed system variants due to low pressure operation.
- More chance for system corrosion to occur due to ‘open vent’ to atmosphere. This could increase maintenance and service costs.
Note the difference between the combi set up and this regular schematic.
There are many benefits to sealing your heating system.
We always recommend this option providing system considerations allow.