The Combi Boiler
A combination boiler (Combi) is an all in one unit for heating your water and supplying heating to your property, they are very efficient because you only pay for the hot water you use as there is no hot water storage. All boilers these days condense which means most of the heat in the flue gas is converted back into energy this can give you 90% efficiency converted in to cash for every pound you spend your only wasting 10p.
How do they work ?
In simple terms, you turn the hot tap on, cold water enters the boiler this then gets heated up through heat exchange and you then instantaneously get hot water delivered at high pressure and because of the high mains pressure hot water these boilers make fantastic high pressure showers with out the need for costly noisy shower pumps.
This all in one unit also heats your radiators again through heat exchange, this process is extremely efficient because of the condensing aspect of the boiler in basic terms hardly any energy is wasted, you can still have your heating controlled via a programmer and room thermostat but the hot water does not need to be timed as it’s instantaneous. For 1 bathroom properties they are perfect easy and cheaper to install and easy to repair and maintain.
What’s the catch ?
There are many different makes, models and outputs in the Combi world unfortunately they do have limitations and the problems are all do do with hot water supply, firstly you need a decent cold water supply into your property because this determines the hot water output therefore low cold in equals low hot out also your Combi has a maximum hot water delivery so basically the hot water has to be shared with the more hot water taps you open at the same time, if you have excellent cold water IN supply and a high output combination boiler (40kw) you will just about get away with a 2 bathroom house with 18 ish radiators anymore than that and you will need stored hot water (cylinder) because of your hot water demand.
The pressure gauge
The dreaded pressure gauge, this can be the most confusing subject but it really isn’t, so in simple terms the pressure in a Combi boiler system is just the quantity of water with in that system, the more water the more pressure and remember as water heats up it expands and will increase the pressure and give you a false reading so when checking the pressure make sure your heating is COLD (sorry for shouting) so when COLD check the gauge youwant anywhere between 1 and 1.5 bar approximately and just to confuse you some Combi boilers need 1.5 bar to run the makes I’ve come across are SIME boilers, some FERROLI boilers but most need 1 bar. Ok so we have low pressure that means we need to add water to the system there are dozens of different makes and models of boilers and most have different ways of adding water therefore I will over the next few months add pictures of as many different boilers as I can.
Combination boilers look good on paper because of the cheaper installation cost and the lack of a hot water cylinder can create more room with in your property but you need to make sure they will provide all the hot water you require, it’s no good having 2 showers if you can’t use both at the same time and a bath that takes 45 mins to fill up !!! (I’ve seen this happen more than once) get some advice from a few suppliers ask the right questions.