Water Heater Not Working? A Repair Guide

Immersion heaters

A dead immersion is usually the element or the thermostat, both inexpensive parts. Scalding-then-cold water means the stat; simply cold means the element or its fuse. In hard water areas elements rarely die of old age, they die of scale.

Instantaneous and multipoint heaters

No hot water at one outlet but fine elsewhere points at the heater itself: scaled heat exchanger, failed diaphragm or a flow rate below the unit's switch-on threshold. Units under eight years old usually earn a repair.

When replacement wins

If the repair costs more than a third of a new unit, or the model is obsolete and parts are hunted rather than stocked, replace. We quote both numbers and let the arithmetic decide.

Electric storage heaters

No hot water at all usually means a tripped thermal cut-out or a failed element. Lukewarm water suggests a thermostat set low or an element part-scaled. Both are inexpensive parts on a sound tank. What is not repairable is a leaking tank, once the cylinder has perforated, replacement is the only honest answer.

Gas multipoint and instantaneous heaters

These fail on ignition, on the flow sensor, or on a scaled heat exchanger. A unit that lights then cuts out after a few seconds is usually a flame-sensing or flue fault, and that is Gas Safe work. Do not keep resetting a gas appliance that is locking out, it locks out for a reason.

Scale is the common denominator

In hard-water London, scale on an element or a heat exchanger is behind most water heater failures we attend. It insulates the heating surface, so the appliance works harder for less output and eventually overheats. Descaling, or a scale reducer on the incoming main, addresses the cause rather than the symptom.

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