What are the different types of boiler?
CONDENSING, NON_CONDENSING
All boiler installed in England and Wales are boilers are now condensing boilers to meet efficiency standards. Condensing boilers are also known as high efficiency boilers.
How to tell; If you have a white plastic pipe coming out of the bottom of your boiler you have one of these. Another way to tell is your flue (exhaust) if this is plastic it's a condensing high efficiency boiler, if it's all metal a non condensing boiler.
COMBINATION BOILER
No external cylinder necessary. The boiler produces direct hot water and does traditional central heating heating without the need for zone valves. Usually best for flats or house with one bathroom. The very best combination boilers can do up to 15 liters/minute fine for two showers simultaneously more might be pushing it (depends on the shower head six bigger - more demand).
(A common mistake my customers make; all boiler can provide you with heating and hot water but that does not make them "combination boilers" this specifically means direct hot water from the boiler not via a storage cylinder
How to tell;
Five copper pipes coming out of the bottom of your boiler.
No external pump or hot water cylinder.
CONVENTIONAL BOILER
Conventional also know as regular boiler or heat only boiler, is your old style boiler with header tank and vent pipe. The pump will always be found on the outside of the boiler. (This can be installed or converted to a sealed system, with an external expansion vessel (red cylinder, with filling link and pressure relief valve) instead of a feed and expansion tank.
How to tell;
Two copper pipes coming out of the top of the boiler.
One copper pipe going into the bottom of the boiler.
Always an external pump.
SYSTEM BOILER
System boilers have most of the components within the boiler itself; pump, expansion vessel, pressure relief valve.
The main difference is instead of a header tank they have an expansion vessel and filling loop (as do combination boilers) with this the heating system is under pressure so much more responsive and efficient.
How to tell;
Three copper pipes attached to bottom of the boiler, none at the top.
No regular external pump (though the still could be an ancillary pump for underfloor heating or return hot water)
No external expansion vessel and no feed and expansion tank (also know as header tank) a small tank usually situated in the loft, (though many flats especially ex and existing social housing may have them at high level in a compartment (most of these have been phased out)
NOT A BOILER
A cylinder such as a Megaflo, or a tradition hot water cylinder is not considered a boiler. These are hot water storage appliances, know as hot water storage cylinders.
INSTANTANEOUS HOT WATER APPLIANCES
An instantaneous gas fired hot water appliance like a Main Multipoint is not technically a boiler, though commonly lay people will refer to them as a boiler.
An Instantaneous hot water appliance refers to an appliance that does not do heating but only instant hot water, no hot water is stored. (In the U.S.A these are being increasingly used and are known as tank-less water heaters, in the U.K. they were once widespread but now are no longer very common)
EXCEPTIONS
There are very few exceptions to the above. Noticeably;
A back boiler, a traditional boiler combined with a gas space heater fire and situated at the back, (hence the name) is also a type of regular or heat only boiler.
A combination boiler that has a built in storage capacity e.g. Vaillant Eco Tec 937 flow rates up to 20 liters per minute suitable for larger properties with two to three bath or shower rooms.
It is possible to use a combination boiler with an external hot water storage cylinder. This would only be done where demand was high and the heating engineer creative. The direct hot water from the boiler can be used for example to supply the kitchen or one bathroom, the heating system would then have to be installed for a system boiler not a combination and the external hot water cylinder would supply the rest of the property. Split supplies with one boiler.