Heating element
A resistive conductor that turns electrical energy into heat — the business end of most electric heating.
What it is
A heating element is a length of resistance wire (often inside a protective sheath) that gets hot when current flows through it. It's the part that actually produces the heat.
How it works
Current through the element's resistance dissipates power as heat. The amount of heat depends on the voltage and the element's resistance. In multi-element banks, the elements share the load across the phases.
Elements fail open (no current, no heat) or degrade (higher resistance, less heat). Sheathed elements can also break down to earth — especially with moisture — which trips earth-leakage protection.
Where it's used
Hot water systems, ovens and cooktops, industrial heater banks, band heaters on barrels, and space heating. Often switched by a contactor or SSR under thermostat control.
What it looks like when it fails
Elements fail open — the contactor pulls in, the controls all work, but no current flows and nothing heats. They also break down to earth, classically only once hot: the element expands, a hairline crack lets the live coil see the sheath, and the RCD trips mid-cycle — then everything tests fine cold.
In multi-element banks, one dead element shows as uneven phase currents and slow heating rather than total failure — nobody notices until the process can't hold temperature.
How to test it
The one-formula test: expected resistance ≈ volts² ÷ watts. A 2.4 kW / 230 V element should read about 22 Ω (230² ÷ 2400). OL is an open element; way over the calculated figure is a degraded one. Test isolated, with at least one lead lifted.
For earth-leakage suspects: insulation resistance from the element terminals to the sheath/earth — low condemns it. Under load, a clamp meter confirms the other direction: current ≈ watts ÷ volts, so that 2.4 kW element should pull about 10 A.
Gotchas
Check the thermostat and its wiring before condemning the element — no-heat calls split roughly evenly between the two. And a brand-new hot water element reading slightly low on insulation may just be moisture in the packing, which often dries out in service — verify against the acceptance value you work to before condemning it.
An element that only trips the RCD at temperature will pass every cold test you throw at it. If the pattern is 'trips mid-cycle, tests fine on the bench', trust the pattern.
Safety first
Elements run at full load current and get very hot. A failed element can leak to earth — never bypass earth-leakage protection. Allow to cool and prove dead.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Related faults
Heater not heating at all
A heater (element, band, or bank) produces no heat — temperature won't rise, the process stays cold, despite the control calling for heat.
Heater bank drawing uneven current across phases
A multi-element heater bank pulls noticeably different current on each phase. Heating is uneven, output is low, or a phase reads much lower than the others.
Heater tripping the RCD / earth leakage
A heater circuit trips its RCD/earth-leakage protection — often when cold and first switched on, or once it's been damp — pointing to leakage to earth from the element.
Related definitions
SSR (Solid-State Relay)
Switches a load electronically with no moving parts — fast, silent, ideal for frequent switching like heaters.
Thermostat
Switches a heating or cooling load on and off to hold a temperature at a setpoint.
Thermocouple
A temperature sensor that produces a tiny voltage proportional to the temperature at its junction.
Contactor
An electrically-operated switch that uses a coil to make or break a load circuit, usually three-phase power.