Immersion heater not working: safe checks before you call

First, is it safe to look?

Open the airing cupboard and look before you touch anything. Water dripping from the cylinder, pipework or the immersion boss, a wet switch, scorch marks on the switch plate, a burning smell, hissing or steam all change the job. In any of those cases, do not touch the switch with wet hands or stand in water. Turn the immersion off at the consumer unit if you can reach it dry and safely, then call for help.

Water that is suddenly scalding, a cylinder that is too hot to touch or banging and steaming pipes suggest the thermostat has stuck on and the safety cut-out has not operated. Switch the immersion off at the double-pole switch or the consumer unit and leave it off. That is an urgent fault, not a reason to keep running hot taps.

Check the double-pole switch and its neon

Most immersion heaters are fed from a double-pole switch near the cylinder, often labelled water heater, with a small red neon. Make sure it is on. On most switches the neon lights when the switch is on and power is reaching it; it does not tell you whether the element is working. A neon that stays dark with the switch on points to a supply problem further back: a tripped breaker, a timer in its off period or a wiring fault.

Dual-element cylinders and some older installations have two switches or a single switch marked bath and sink. The lower element heats the full tank and the upper element heats only the top portion. If one setting gives hot water and the other does not, one element or its thermostat has probably failed.

Timers, Economy 7 and the clocks

Many immersion heaters run through a timer so they heat on cheaper night-time electricity. A plug-in or wall timer that loses power can reset to the wrong time or wipe its programme, so a power cut is a common reason for no hot water from immersion the next morning. Check the clock shows the correct time, then check the on periods.

Citizens Advice points out that off-peak times depend on your supplier, tariff and area, and may change when the clocks change. If your tariff or meter has changed recently, ask your supplier for the current off-peak window and reset the timer to match. Some Economy 7 homes have a separate off-peak supply that switches on only overnight; if it fails, the immersion will be cold even though everything else in the house works. Contact your supplier about the meter or switching equipment rather than touching it.

Tripped breaker or RCD: reset once only

Look at the consumer unit for a breaker labelled immersion or water heater that is down, or an RCD that has tripped a whole bank of circuits. Switch the immersion off at its own switch, reset the breaker or RCD once, then switch the immersion back on. If it trips again, leave it off. Repeated immersion heater tripping the electrics often means the element sheath has cracked and water is reaching the conductor, which is a fault to be tested, not forced.

If the whole street is dark, it is a network fault: report it to Electricity North West on 105. When the power comes back, recheck the immersion timer, because it may have lost its time while the supply was off.

Cold or lukewarm: reading the symptoms

Completely cold water with the switch on and the neon lit usually means one of three things: the element has burnt out, the thermostat has failed open, or the thermostat's high-limit safety cut-out has operated. The cut-out is designed to switch the heater off if the water overheats. It sits under the immersion cap next to live terminals, so an immersion heater thermostat reset is a job for an electrician, who will also find out why it tripped rather than just resetting it.

Lukewarm water that never gets properly hot suggests a thermostat set too low or drifting, a failed lower element on a dual-element cylinder, or simply heavy use that empties the tank faster than it reheats. HSE guidance is that stored hot water should reach 60C or above to control legionella, so a cylinder that never gets there needs looking at as well. An electrician tests the element resistance and insulation and the thermostat operation with the supply isolated, which tells you whether the immersion heater element failed or the control did.

What about limescale?

In hard water areas, scale builds up on immersion elements and can make them noisy and slow, or shorten their life. Most of Greater Manchester receives relatively soft water, so heavy scaling is less common here than in many parts of southern and eastern England, although it can still happen on an old element. A crackling or fizzing cylinder is worth mentioning when you call. Vented copper cylinders in airing cupboards are still common in older terraces and semis across Didsbury.

Plumber or electrician?

An electrician is the right first call for a dead switch, a tripping circuit, a scorched switch or flex, a failed thermostat and testing the element, which is what our fault finding visits cover. Replacing an element means draining down at least part of the cylinder and resealing the boss, which some electricians do and some leave to a plumber or heating engineer. Leaks from the cylinder, valves or pipework are plumbing work, though the electrics nearby should be checked once the leak is fixed.

Pressurised unvented cylinders carry safety valves that should only be worked on by an installer qualified for unvented systems. If your hot water normally comes from a gas boiler and the immersion is a backup, a boiler fault needs a Gas Safe registered engineer. Tell us which kind of system you have when you call, and we will say honestly whether it is our job.