Storage Geyser With Hot Water Failure
A 15-litre, 2 kW, 230 V storage geyser in a Nagpur bathroom has stopped giving hot water. The neon indicator on the geyser glows whenever the switch is on, but the water stays cold even after 40 minutes. The neon is wired across the supply terminals after the thermostat, so it lights whenever power reaches the unit. The owner has replaced the 15 A fuse in the plug top and confirmed 230 V at the geyser terminals. A multimeter is available. The installation has a 16 A MCB and a proper earth. The thermostat knob is set at 60°C. The thermal cutout is a one-shot type mounted on the tank, and the element is a flanged type that can be removed after draining the tank. The bathroom is on the first floor and the geyser is supplied through a 16 A switch.
1. Describe a safe, logical test sequence to locate the fault, stating the expected readings and what each reading proves.
Read the worked answer
- Isolate the geyser at the double-pole switch and MCB, then verify dead with a tester.
- Close the inlet and drain the tank, or let it cool fully, before opening the element.
- Inspect for burnt wiring, loose terminals, scale and water leakage.
- Disconnect the element and measure its resistance. A good 2 kW, 230 V element reads about 26.5 Ω; 'OL' means an open element.
- Check thermostat continuity at room temperature. With the knob at 60°C and the tank cold, the thermostat should be closed and read near 0 Ω.
- Check the one-shot thermal cutout continuity. It should be closed; open means it has operated.
- Check element insulation resistance from terminal to tank, which should be at least 1 MΩ at 500 V DC.
- If all components are continuous, re-energise and measure voltage from the incoming terminals to the thermostat, cutout and element. A healthy circuit shows about 230 V up to the break and 0 V after it.
Each voltage step localises the break; each resistance step proves whether the component itself is open or closed.
2. With the unit energised and the switch on, you measure 230 V at the incoming terminals but 0 V directly across the element terminals. What does this tell you? How does this differ from an open element?
Read the worked answer
0 V across the element means there is no potential difference being applied to it. Since one side of the element is connected to neutral, and no current is flowing, the other side is also at neutral potential because the circuit is open upstream. The break is therefore in the thermostat, the thermal cutout or the wiring between them, not in the element.
If the element itself were open, the full 230 V would appear across the element terminals. The upstream path would be complete, no current would flow, and there would be no voltage drop anywhere except at the break, which is the element.
This is the key diagnostic distinction: 230 V across the element with supply healthy indicates an open element; 0 V across the element with 230 V at the incoming terminals indicates an open switch, thermostat, cutout or wiring upstream. Replace the faulty component, not the element.
3. The thermal cutout is found open. The owner wants it bypassed because 'the thermostat already controls temperature'. Explain why this is unsafe and what must be checked before fitting a new cutout.
Read the worked answer
The thermal cutout is an independent fail-safe limit. It opens if the thermostat sticks closed, if the tank overheats, or if the element runs dry. Bypassing it leaves the thermostat as the only control; a stuck thermostat would then boil the water, raise tank pressure and risk steam release, scalding, and element or tank failure. The cutout is not a duplicate of the thermostat, and it must never be shorted out.
Before fitting a new cutout, check the thermostat for sticking, because it may be the real cause. Check for heavy scale on the element, which causes local overheating. Confirm that the replacement cutout has the same temperature rating and type as the original. Check the element insulation and the earthing, and confirm the wiring. Refill the tank before switching on, never dry-heat the element, and test the cut-out temperature after reassembly. If the new cutout operates again, find the underlying cause rather than repeatedly replacing it.