Heating Appliances (Electric Iron, Heater, Geyser, Oven, Induction Cooktop)
What this domain tests
Heating Appliances covers electric iron, room heater, geyser, oven and induction cooktop. The exam checks heating-element principles, thermostats, thermal cutouts, insulation, earthing and appliance-specific faults.
Core rules
- Most elements are nichrome resistance wire. Cold resistance is lower than hot resistance, so a calculated R = V²/P is only an approximation when the element is cold.
- A bimetallic thermostat cycles the element; a thermal fuse or cutout is a one-shot or resettable safety device and must never be bypassed.
- An electric iron uses a soleplate, thermostat and pilot lamp. A geyser uses an immersion element, thermostat, pressure-relief valve and sacrificial anode. An oven uses elements, thermostat, timer and door interlock. An induction cooktop uses a coil, IGBT switching and pan detection; it heats only ferromagnetic cookware.
- Metal bodies must be earthed. Insulation resistance and earth continuity are safety-critical tests.
Worked example
A 1500 W heater does not heat. At 230 V the expected current is 6.52 A and the hot resistance is 35.3 Ω. With the heater isolated, a continuity test shows an open circuit across the element, while the thermostat is closed. Reasoning: the element has failed. Replace it with the same wattage and voltage rating, check the thermal cutout and earth bond, then test insulation before returning the appliance.
Traps that cost marks
Testing an element while it is live; fitting a higher-wattage element than the appliance is rated for; bypassing a thermal fuse; using an induction cooktop with an aluminium pan; and ignoring a low insulation reading because the appliance still heats.