The Boiler. The heart of the machine. No hot water - no coffee. Now this is one of those occassions where size may be important. The larger the boiler (in litres) the less of a temperature drop when you brew coffee or draw water. Think of it this way - if you take a cup of water from a boiling two cup kettle the temperature will fall by ~50%, take a cup from a boiling ten cup kettle the temperature will only fall by ~10%. This is important as the coffee will taste differently when brewed at different temperatures, so if you plan to use the espresso machine as a source of hot water (for say plunger coffeemakers or cups of tea) and the boiler is too small then there will be a wait till the temperature climbs back to the correct level - not very clever if you've got a queue of customers. Mind you the bigger the boiler the longer to get to temperature from cold, so lets look at .....(it does occur to me that some espresso machines use "flash" boilers. These clever(?) devices literally heat the water on demand - like for example an electric shower. Now the manufacturers will claim all sorts of advantages (they would wouldn't they), suffice it to say that for coffee there should be a problem but if you require water best to take claims with a pinch of salt and remember that the temperature of the water going into the machine is much colder in winter!)

The Power Source. The very first espresso machines used open fires to heat the boiler and it is still possible to get espresso machines which will run on a gas burner supply. However to all intents electricity is the usual power source. As with the boiler, size can be important. It is possible to get machines which will run from a standard 13A plug, however you are going to be restricted to the size of element availble - maximum of ~2.8kW. If you want to get some idea of how this will work fill your kettle with a litre of water and time it to boiling. Take that time and multiply it by the number of litres in the machine boiler and that's your time to ready from cold! The usual connection is through a standard "cooker" type fixed connection, so you'll need to organise another fuse in the fuse box!

The Pump. This pushes the water into the boiler and through the coffee. This is usually split into two parts- - the pump bit which physically moves the water and the motor which turns the pump. Not a lot to say really some machines have these as an external part which means you'll need to allow for them in the plans of the site otherwise it is important that they should have "two screw" access. If they fail you don't really want to have a major repair job on your hands.

The Control Gear. All the sensors that check for the boiler being full of water, at the correct temperature, at the right pressure. Not a lot to say about these parts - when they do their job they're invisible, when they don't ......It goes without saying that these should all have easy access for replacement (no you just don't repair things anymore) purposes.

Part Three - outside the machine