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Combi boilers, in a nutshell, combine the ability to provide hot water and central heating in one compact box.  But before you rush out and start googling your nearest Gas Safe registered installer, it would be advisable to find out a bit more about the advantages and disadvantages of a combi boiler, so please read on and if you have any questions at the end then let me know.

How do combi boilers work?

The hot water is provided via the cold water mains which passes through the boiler and is heated on demand, when I say “on demand” I mean if you want hot water you open a tap, the boiler then heats the water before it gets to the tap outlet, once you have finished washing the dishes or taking a bath, you turn the tap off, which sends a signal to the boiler (via a flow switch) and the boiler stops heating the water.

The Central Heating works in much the same way, the water is pumped around the central heating circuit when you “call for heat” via a room stat/programmer, once the required temperature is reached the boiler switches off. All combi boilers are now condensing which means that they cool down the flue gases to produce energy, which in turn improves efficiency and lowers running costs , this process causes a build up of condensation which is acidic,  the condensate leaves the boiler via a plastic pipe and terminates in a drain or waste pipe (so bear in mind that you will need to site your new boiler near a drain).

New condensing combi boilers are fan flued, which means that they have a fan which is used to suck the fumes in to the outside air via the flue, this method increases the safety of your appliance, as the boiler will not “fire up” unless the fan is running.

Advantages over a system boiler

A system boiler is a central heating boiler which uses a hot water storage tank to store hot water until the user needs it, this is obviously costly, as unlike a combi you are heating the storage tank up regardless if  your using the hot water or not, whereas with a combi its “on demand”, so the first advantage is its cheaper to run.

The second advantage is space, with a combi  boiler you only have the boiler, and everything your system needs is contained within the one box, so the tank, 3 way valve, tank pipe work, header tanks, and anything else associated with a system boiler can be removed freeing up a lot of storage space in your home.

With a combi boiler you will often find an increase in pressure compared with your old gravity or fully pumped system (especially gravity fed) this does depend however on your cold water pressure.

Disadvantages of a combi boiler

For the life of me I can only think of one disadvantage of a combi boiler, and that is the hot water flow rate. In a nutshell a combi can only produce between 10 and 16 litres of water per minute (depending on boiler size), so if you had 2 showers that were often used at the same time, then I would advise against a combi, as one of the showers would run cold, as the boiler could not keep up with the demand. However if you have only one shower or one bathroom then I would recommend a combi, even if you did have 2 showers/bathrooms as long as you were happy to only have one in use at any given time, then a combi would still be the system I would recommend. A system boiler will give you as much hot water as you need due to the capacity of the hot water tank.

NOTE: Some combi boilers do contain small storage tanks, which can combat this problem to a certain extent.

I hope this article has broadened your combi boiler installation knowledge, and helps you make the correct decision, if you would like to discuss this article or just want something clarifying then feel free to give us a call by clicking here.