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What is A Combi Boiler

cobi boiler layoutCombi boilers, in short, blend the capability to supply hot water and central heating in one compact box. But before you rush out and begin googling your nearest Gas Safe registered installer such as this gas engineer in Cambridge, it could be wise to learn a bit more about the advantages and disadvantages of a combi boiler, so please read on .

How do combi boilers work?

The hot water is supplied via the cold water mains which goes through the boiler and is heated on-demand, when I say “on demand” I mean if you need hot water you open a tap, the boiler then heats up the water before it reaches the tap outlet, once you’ve finished cleaning the dishes or having a shower, you switch the tap off, which delivers a signal to the boiler (by way of a flow switch) and the boiler ceases heating the water.

The Central Heating works in much the same manner, the water is pumped around the central heating circuit when you “call for heat” via a room stat/programmer, once the demanded temperature is achieved the boiler turns off. All combi boilers have become condensing which means they cool-down the flue gases to generate energy, which consequently improves efficiency and lowers operating costs , this process leads to a build up of condensation which is acidic, the condensate leaves the boiler via a plastic pipe and ends in a drain or waste pipe (so keep in mind that you will have to site your new boiler near a drain).

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

system boiler layoutStrengths over a system boiler

A system boiler is a central heating boiler which uses a hot water storage tank to store hot water up until the user needs it, this can be clearly costly, as in contrast to a combi you’re heating the storage tank up regardless of whether your using the hot water or not, whilst with a combi its “on demand”, so the first advantage is its less expensive to operate.

The next advantage is space, with a combi boiler you only have the boiler, and everything your system needs is contained in the one box, so the tank, 3 way valve, tank piping, header tanks, and everything else associated with a system boiler can be taken out freeing up lots of storage space in your home.

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

Disadvantages of a combi boiler

I can only see a single problem with a combi boiler installation, and that is the hot water flow rate. In a nutshell a combi is only able to produce between 10 and 16 litres of water every minute (depending on boiler size), so if you had 2 showers which were often used simultaneously, then I would advise against a combi, as one of the showers would run cold, as the boiler couldn’t maintain the demand. If however you have just one shower or one bathroom then I would certainly suggest a combi, even if you did have 2 showers/bathrooms providing you were happy to have only one in use at any time, then a combi would still be the system I would suggest. A system boiler provides you with as much hot water as you need because of the capacity of the hot water tank.

NOTE: Some combi boilers do include smaller storage tanks, that may combat this problem to some degree.

I hope this article has enhanced your combi boiler installation know-how, and will help you make the correct decision.