We are redesigning the baptistry water heater, so in the New Year, this will only apply to 4.8kW heaters shown here.
With the 4.8kW heater, one element is the master and the other the slave. Both are independently earthed but the earth on the ‘slave’ flex will not work unless the master is plugged in and switched on. So, unless you have two PAT testing kits, it is important to get the correct plug.
To get an earth, the usual thing to do would be to touch the heating elements with the earth probe. The coil manufacturer advises that a contact should be sought at the base of the coil (see the photograph).
The 4.8kW water heater has two plugs and we mark the flex for the master element with a piece of black tape so you get the correct plug. Then one needs to make a test on both elements (at the base of the element). Even then, scale on the elements can give a false fail, and I have found that the ‘pencil-like’ earthing probe doesn’t get enough contact. Most kits come with an alternative ‘dog-tooth’ clamp fitting to go on the end of the earth probe.
To get at the coils, unscrew the 4 corner screws and lift out the top plate (picture 1). The coils are attached to this and should lift up with it. Use the clamp to scrape away at the scale and get a better contact.
Summary – Use the plug with black tape on flex, and get a good contact on the coil.