Geyser not heating, leaking or tripping the MCB: what each fault means

Most geyser faults fall into five groups, and each one points at a short list of causes. No hot water is usually the thermal cut-out, the element or the thermostat. A leak is a fitting, the relief valve, the element gasket or the tank, in rising order of seriousness. Water too hot or too cold is the thermostat. The MCB or RCCB tripping is a leaking element or damp wiring. Slow heating is scale. Here is how to tell them apart, and what is safe to check before anyone visits.

No hot water at all

Lamp off, nothing happening. Check the switch, the socket, and the MCB for that circuit. If the MCB has tripped, reset it once. If it trips again, stop — that is the next section.

Lamp on, water cold. Three usual causes, all inside the unit:

• The thermal cut-out has tripped. This is a safety switch that opens if the water overheats, often because the thermostat stuck on. It sometimes resets by itself once cool; if it keeps tripping the thermostat is the real fault.
• The element is open-circuit. Common on older geysers and on hard water, where scale makes the element run hot until it burns out.
• The thermostat has failed open and is never calling for heat.

On a digital geyser the control PCB is the fourth possibility, especially after a voltage spike. All of these are behind the cover. Switch off at the MCB and book it as "no hot water" — ₹399 for diagnosis and standard labour, parts at MRP shown before fitting.

Leaking

Where the water comes from tells you how serious it is.

Where	Usually	How serious
Inlet or outlet connection	Loose fitting, worn thread tape, a cracked flexible hose	Minor — tighten or replace the fitting
Relief-valve outlet, drips only while heating	Normal expansion	Not a fault
Relief-valve outlet, steady drip or flow	Valve worn or seated on grit; or inlet pressure too high	Valve replacement; check pressure
Bottom cover, near the element	Element gasket or flange seal	Gasket replacement, element checked at the same time
Body or bottom of tank, rusty water	Tank corroded through	Not repairable — replace the geyser

Any leak near the electrical side means MCB off before anything else. A leak repair is ₹350 on the rate card; a tank leak is a repair-or-replace conversation, and we have a separate guide for that.

Water too hot, too cold, or swinging

The thermostat sets the temperature and switches the element off when it gets there. When it drifts, you get lukewarm water at the same setting as before, or water so hot that the relief valve starts dripping and steam comes out of the tap. When it sticks on, the thermal cut-out trips and you get nothing.

If turning the knob makes no difference, or the geyser seems to heat far past where you set it, it is the thermostat. Replacement and calibration is ₹399 plus the part. Do not try to "fix" an overheating geyser by turning the thermostat down and living with it; the cut-out is the only thing between that and a boiling tank.

MCB or RCCB tripping

RCCB (the earth-leakage switch) trips when the geyser is switched on. Nine times out of ten this is the element: the sheath has cracked and current is leaking into the water. The RCCB is protecting you. Leave it off and book the repair.

RCCB trips only in the monsoon, or only first thing in the morning. Damp has got into the terminal box, the plug or the switch. Common in October–December when the bathroom never dries. It still needs fixing — a damp earth path is a shock path.

The MCB (not the RCCB) trips. Either a short circuit in the wiring or element, or the circuit is overloaded. A 3 kW or 4.5 kW instant geyser on a 10 A MCB or thin wire will trip every evening when the supply voltage sags and the current rises. That is an installation fault, not a geyser fault.

Resetting a breaker repeatedly to "see if it holds" is the one thing not to do.

Takes too long to heat

A 15 L, 2 kW storage geyser should bring cold water to bathing temperature in roughly fifteen to twenty minutes; a 25 L unit in about half an hour. If it has stretched well past that:

• Scale on the element — by far the most common reason on borewell water. A flush and descale fixes it.
• Thermostat set low — check the knob before anything else.
• Low voltage — in the evening dip a resistive heater simply heats slower.
• One of two elements failed on a larger geyser.
• A 10 L geyser for a family of five — not a fault, a size problem.

Noises, smells and tingles

Rumbling or popping while heating is sediment boiling at the bottom of the tank — flush it. A smell of hot plastic at the switch or plug means a loose, overheating connection; switch off at the MCB. A tingle from the tap or the geyser body is an earth fault: MCB off, do not use it, and have the earthing and the element checked the same day you notice it.

When to call

Anything behind the cover, anything involving a trip, any leak you cannot trace to a fitting, and any tingle. What you can do yourself is the switch, the socket, the MCB once, the thermostat knob and a look at where the water is coming from — usually enough to describe the fault accurately when you book.