This job is not particularly difficult to do, however if you do not feel confident to do it, then you should call a professional plumbing service like the ones for Finchley Boiler Repair.NOTE: If the old pump is defective always make sure you have the correct replacement booster pump. A). Isolate the power and the water supply to the shower. Confirm that they are isolated correctly. If available open the drain-cock to release any water from the pump pipework. If not prepare for some water discharge when you disconnect the pumps pipework. These connections are normally flexi with push-fit or compression joints and the new unit should be the same making the re-fit really straightforward. B). Next, unbolt the broken pump from its base and disconnect the electrical cables from its terminals. You should use a voltmeter to ensure that no electrical voltage (240ac) is present even though it is isolated (trust your testers). When this is done, remove the pump. When you are happy, re-fit the new pump in reverse order. Finchley Boiler Repairs carry out work in accordance with current Regulations.TIP: A good idea is to make a drawing of electrical connections or even take a photo to ensure correct re-connection.On Completion:Turn the water supply back on and check all the pipework for any leaks that may occur. Connect the new pump into its supply point (usually a 3 pin 13 amp socket outlet). If there are no flex connections provided there will be a need to modify the pipework to achieve this. During this process a great deal of care must be taken so as not to damage the plastic water connections on the replacement pump with heat from any soldering procedure if it needs to be done. You must try very carefully not to cross thread any of the plastic connections.