How to Fix an Immersion Heater Not Working

Overview

An immersion heater that is not working can leave you without hot water. This guide covers diagnosing and fixing the issue.

Step-by-Step Fix

1. First, always prioritise your safety by switching off the main electricity supply to your property at the consumer unit (fuse box) before touching any wiring. Locate the dedicated circuit breaker or fuse for your immersion heater on your consumer unit and check if it has tripped (it will be in the 'off' position or an RCD will be down). If it's tripped, switch it back on, then try the immersion heater again; if it trips immediately, there's a fault that needs further investigation.
2. Ensure the immersion heater's timer switch, if fitted, is correctly set for the hot water demand and hasn't been accidentally turned off. Manually override the timer to the 'on' position to see if the heater starts working immediately. If it's a simple timer issue, reset it to your desired schedule.
3. Before proceeding, make absolutely sure the electricity supply to the immersion heater is isolated at the consumer unit. Carefully locate the small red or black reset button, usually found on the top or side of the immersion heater's thermostat cover. Press this button firmly; you should hear a small click, indicating the thermostat has reset.
4. If the reset button on the thermostat trips again very soon after being pressed, or if it immediately trips the circuit breaker, this strongly indicates a serious electrical fault. Do not attempt to operate the immersion heater further without professional assessment. At this point, it is advisable to contact a qualified electrician or plumber.
5. With the power still safely off at the consumer unit, disconnect the wiring to the heating element at the immersion heater. Using a multimeter set to measure continuity or resistance (Ohms), place the probes across the two main terminals of the heating element. A healthy element should show a resistance reading, typically between 15-30 Ohms; a reading of zero or infinity (open circuit) indicates a faulty element.
6. If your multimeter test confirms the heating element is faulty (either zero or infinite resistance), it needs to be replaced. Replacing an immersion heater element involves draining the hot water cylinder and working with plumbing and electrics, which can be complex and dangerous if you're not experienced. If you're not confident undertaking this DIY task, it is highly recommended to call a qualified plumber or electrician to carry out the replacement safely.

Common Symptoms & Diagnostic Resolutions

Review the common error codes and operating symptoms below to quickly identify the root cause of the fault before ordering replacement parts.

Frequently Asked Questions