An electric shower is a relatively straightforward thing to install but there are several factors that you must consider beforehand. They require a minimum water pressure to work - usually around 1 to 1.5 bar - and will also have a minimum flow rate requirement. Details of this will be included in the manufacturer's detail sheet.
It is generally best to get the plumbing side of things done first so that you can test your work fully without any electrics nearby. Obviously if there are electrics in the vicinity you must isolate this at the consumer unit before carrying out any work.
These shower units are normally fed from the rising main in your house. It may be possible to feed from its own dedicated supply from the cold water storage cistern in the attic but the chances are that this will not provide an adequate head and the resulting poor pressure will be insufficient.
The water supply is run in 15mm pipe work. This may be copper or plastic depending on your preference. If the pipe work will be hidden, plastic is the more usual choice and is generally easier to work with.
Decide where the shower is going to be mounted. Take into account the ease of accessing a suitable route for both the plumbing and the power supply. Also ensure that it will be mounted over a suitable shower tray or bath and that the surrounding area is sealed. To ensure there can be no backflow or contamination, the shower head should not be able to reach within 25mm of the highest likely water level. If this requirement cannot be achieved, a suitable double check valve must be fitted in the supply pipe.
Decide on the entry point on the shower unit to be used for the water. Most units have cut outs available for side, top, bottom, and back. Using the back option will hide the pipe work completely. Hold the unit against the wall where it will be mounted and mark the entry point with a pencil. Put the unit back in its protective packaging to keep it dust and dirt free.
Identify how you are going to run the 15mm supply to the marked position. If you’re lucky this will be on a stud work wall which will make routing the pipes much easier. If not, you might want to consider battening out a false wall rather than having to chase brick or block work for the pipe. Remove the plasterboard from this shower wall and replace with WBP plywood. This is far more durable for mounting the shower and should be sealed to prevent it absorbing any moisture. Loose fix the ply and cut out the marked entry point for the water pipe.
The ply should also have a cut out for the cable needed to supply power. See later details regarding electrics, but if you have the correct cable ready, you can install this now and simply run it back to a convenient point ready for later connection to the consumer unit. Otherwise, leave a draw string running from here to a suitable access point so that the cable can be pulled through when ready.
Assuming that you are connecting to the rising main at the nearest available point, you should now turn off the main stop valve. Drain the water from this pipe using the drain point adjacent to the valve or, if there isn’t one, run the cold at the kitchen tap till it stops.
Cut the pipe and fit a Tee with a 15mm outlet. Run your new pipe work from here to the shower unit and include an isolating valve at an easy to access point. This will allow you to turn the water to the shower off for maintenance. Run the pipe work inside the wall up to the shower and out through the previously made cut out. Make sure the isolating valve is closed, and then open the mains stop valve and check your work to ensure there are no leaks.
Mounting the Electric Shower
Take the back plate off the shower and hold this against the wall in position. Mark the fixing points and the drill and plug as required. Fix the back plate to the wall but do not fully tighten the screws yet. This will allow you to make adjustment for square once the plumbing is connected. If you are using copper pipe, when making the plumbing connections, do not use any jointing compound, or solder joints near the shower as heat transferred along the pipe can damage it.
Make the final water connection to the shower inlet. Check the manufacturer’s instructions for this but it will normally be with a brass compression fitting. Align the back plate so that it’s perfectly square and level then tighten the fixing screws.
Note that it is a good idea to seal around the pipe where it comes through the wall to ensure that no water can get down inside the wall and cause damp problems later.
Electrics for the Shower
The load for an electric shower is high and the electricity supply in your home must be checked to ensure that it can cope with the additional load. If your supply is inadequate, you will need to speak to your supplier and you may well need a new consumer unit.
Most electrical work is now notifiable under Part P of the Building Regulations. Essentially, this means that the work must be carried out by a Registered Electrician. If a competent home owner wishes to do the work themselves, they must submit a Building Regulations application, pay a fee, have a Building Control inspection at first fix stage, and then have the work tested on completion. In reality, this means that the later is more expensive in the long run and it is better to have a professional installer do the work
The electrical supply for the shower requires a separate dedicated supply from the consumer unit and involves work in a bathroom. Residual Current Device (RCD) protection of the circuit is also needed as well, and appropriate earth bonding of metal work. This is all notifiable work so the safest, and usually most cost effective route, is to have this aspect of the job carried out by a professional electrician.
The MCB at the consumer unit will be determined by the rating of the shower. For example, a 7kW shower will need a 32 amp MCB, a 9.5kW will require a 40 amp MCB and a 10.5kW shower will need a 45amp MCB. The twin and earth cable required for the supply from the consumer unit will depend on a number of factors including the rating of the shower and your electrician will determine whether this will need to be 6mm2, 10mm2, or larger.
A double pole isolating switch must be included in the power supply and this is commonly fitted outside the bathroom in a convenient location safely out of the reach of anyone using the shower. It is possible to have this fitted inside the bathroom but, in this situation, it must be a pull cord type which guards against possible electric shock.
The live, neutral, and earth will be connected by your electrician to the terminal block inside the shower unit and the cable will be passed through a cable clamp to secure it. The earth conductor will also be sheathed with green and yellow sleeving. Once the electrics have also been connected to the shower unit following the manufacturer’s instruction, and the cover fitted securely, you will be ready to commission it.
Commissioning the Electric Shower.
Fit the shower hose to the unit but without the shower head. Leave the shower hose directed at the waste outlet / into the bath. With the power supply to the shower switched off at the double pole isolating switch, check that the shower control is set to off or stop, and set the temperature selector to maximum (minimum water flow). Turn the water isolating valve on and inspect. All being well, turn on the power supply. The power indicator on the unit should now be lit.
Turn the shower on using the cold setting and allow it to flush through to remove any debris or dirt. This also allows the heater unit to fill before the elements are switched on. With the unit still set to cold, turn the temperature dial to minimum (max water flow). Continue the flushing until the water flows steadily and all air has been released. Turn off again and connect the shower head to the hose before final testing with the unit set to a reasonable temperature.