What are the parts of an immersion heater element?
What are the parts of an
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When attached to the cylinder… |
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When attached to a hot water cylinder, the only part of an immersion heater element that is visible is its casing. The element coil and thermostat extend inside the cylinder. | |||
Immersion heater fibre washer |
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A fibre washer (also known as a fabric seal) prevents leaks by plugging the gap between the immersion heater element and the copper boss or flange it has been screwed into. | |||
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The material from which the washer is made expands when it gets wet, which means it has a built in anti-leaking mechanism!
The washer will conform to the surfaces it is sandwiched between – in other words, it changes shape to mould around any minor lumps and bumps. |
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Immersion heater element coil |
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The element coil is the part of the immersion heater element that heats the water. | |||
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When switched on, the element coil works in exactly the same way as a kettle. Electricity passes through the wire in the coil, which becomes hot. This heat is then transferred to the water in the cylinder. | |||
Immersion heater thermostat |
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The thermostat is the only component in the immersion heater element that extends into the hot water cylinder but is visible beneath the casing. | |||
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The long rod at the back of the thermostat allows the device to take the temperature of the water inside the tank.
The rod of the thermostat fits into a sleeve so that it can be removed easily and without draining the cylinder. |
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The head of the thermostat is usually plastic and contains the control dial that allows the user to select the temperature of the water in the tank. | |||
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This is usually set between 60˚ and 65˚ centigrade. | |||
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An immersion heater element thermostat unit actually contains two thermostats. One allows you to manually adjust the temperature of the water in your hot water cylinder. The other is a limit thermostat that is built into the unit as a fail safe. | |||
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If the main thermostat fails, the limit thermostat will ensure that the heater cuts out at around 85˚ – 90˚ centigrade in order to prevent the water in your cylinder from boiling. It does this by cutting power to the element. When this happens, the immersion is said to have tripped. | |||
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This is a safety device and will not reset automatically. Manually reset the trip by inserting a small object, such as a paper clip, into the reset hole and push to reset.
If the thermostat trips again, or on a regular basis, call a qualified plumber for advice. |
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Sometimes this limit thermostat can trip accidentally (particularly if you cover the immersion heater casing with clothes) which can cause heat to build up and fool the thermostat into thinking the water in the tank is hotter than it actually is.
So make sure you don’t bury your immersion heater element in laundry! Never cover the thermostat. keep clothes and insulation well away to avoid nuscience tripping. |
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Immersion heater element base |
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The base of the element has a screw thread that helps the immersion heater element attach securely to the hot water cylinder without leaks. | |||
Inside the immersion heater casing |
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WARNING – removing the casing will reveal live parts. When replacing an immersion heater element, you will need to remove the casing by removing the nut at the top. This will then expose the wiring and the thermostat control. |
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There are three posts beneath the immersion heater element casing. A red or brown insulated wire connects the Live post of the element to the thermostat. The mains cable will have three wires, a brown (Live) wire connected to the other side of the thermostat, a blue (Neutral) wire connected to the Neutral post of the element, and a green and yellow earth wire attached to an extended screw which is usually the same screw that is used to secure the element casing. | |||
