How to install an immersion heater

This guide should only be used by qualified personnel who should follow the latest IEE regulations and site regulations.

Immersion Heater Installation, Wiring And Maintenance Instructions


When you fit the heater, allow enough space that the element is not covered by any silt or deposits at the bottom of the tank.
Ensure that the thermostat or cutout, if fitted, and offset in the heater, are at the top side of the element bundle.
Make a drip-proof seal between the heater and the tank, leaving enough room to withdraw the heater.
Mount the heater away from shock, vibration, explosive or hazardous atmosphere or dust-laden or corrosive environments—unless specifically designed for such applications.


The mains supply voltage available to power the heater must correspond with the supply voltage stated on the heater nameplate. If the heater is so designed, the neutral line should be connected.
2.2 Ensure that the sizes of supply cables and contactors are adequate for the electrical load they carry.
2.3 If the heater is divided into anumber of stages, then the section of elements adjacent to the safety cut out probe must be wired into the first heater stage, ie, the stage that is continuously switched on whilst the heater is energised.
2.4 Chech that the thermostat / safety cutout, if fitted, is corectly wired to ensure complete shutdown of the heater, ie, in series with the coil of the main contactor. Ensure the rating of the conatactors and the fuses are adequate.
2.5 Check that a sufficently good earth is conneccted to the heater unit.
2.6 check all electrical connections for tightness, including all element terminations.
2.7 check that the terminal cover is correctly fitted before switching the heater on.


3.1 Check that the active part of the element is well covered by the fluid.
3.2 It is general practice for control to be automatic, a thermostat is used to sense any change in heat requirement and then operate the heater directly (up to 3kW) or through a contactor (over and above 3kW).
3.2 iIn the event of shutdown caused by overheating, the main isolator must be switched off before checking the system. The fluid level should be checked and the control systems inspected. Reset the cutout (if fitted).


4.1 The heater must be isolated before removing the terminal cover, and should not be switched on until the terminal cover has been replaced and the system refilled with fluid.
4.2 Periodically inspect the heater to ensure that there is no build up of deposit on the elements.

This guide should only be used by qualified personnel who should follow the latest IEE regulations and site regulations.


Wiring specifications have altered over the years, as detailed below –

 Pre-1977 IEEPre-2004 IEECurrent IEC
Protective earth (PE)GreenGreen/yellow bi-colourGreen/yellow bi-colour
Neutral (N)BlackBlackBlue
Single phase: Line (L)RedRedBrown
Three-phase: L1RedRedBrown
Three-phase: L2YellowYellowBlack
Three-phase: L3BlueBlueGrey

For further detail, here are the IEE Wiring Regulations

3 phase

An example of a correctly wired 3-phase heater, kindly supplied by one of our customers –

You can find more techincal info about industrial immersion heaters at the Process Heating Services website.