Water Heater Not Working? A Repair Guide
Immersions, multipoints and wall heaters fail in predictable ways.
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If the repair costs more than a third of a new unit, or the model is obsolete and parts are hunted rather than stocked, replace.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.
What the fault code is really telling you, what's safe to try, and when to stop.
Five checks that fix a surprising share of no-hot-water mornings for free.
Valve, spindle, tail or the panel itself, each one leaks differently, and only one of them means a new radiator.
A sealed system does not consume water. If you are topping up, it is going somewhere, and where matters.
Sediment makes cylinders rumble, slows heating and kills elements. Flushing it is routine maintenance.