Ravenheat E24 Fault Code: Causes, Fixes & Repair Costs
What does the Ravenheat E24 fault code mean?
The E24 code on a Ravenheat boiler indicates a fault with the heating return NTC thermistor — the small temperature-sensing component clipped or screwed onto the return pipework inside the boiler. This sensor monitors the temperature of water flowing back into the boiler from the central heating circuit. When the PCB receives a signal that is out of range, implausible, or missing entirely from this sensor, it cannot safely track the heating circuit's thermal state and will lock the boiler out as a precaution. In plain terms: the boiler's electronics have lost confidence in the return temperature reading and have shut down to prevent potential overheating.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or failed return NTC thermistor Common
After years of service, the thermistor bead itself degrades — particularly in systems with hard water, where limescale deposits build up around the sensor pocket and cause localised overheating. The sensor's resistance drifts outside the range the PCB expects, triggering E24. This is by far the most frequent diagnosis on these boilers.
- Damaged or corroded sensor wiring Common
The wiring harness running from the return sensor to the PCB can chafe against the edges of the heat exchanger or other internal metalwork. Over time this causes fraying, intermittent open-circuits, or short-circuits. The fault may come and go initially, making it look like a soft lockout, before becoming permanent.
- Poor electrical connection at the sensor plug or PCB header Sometimes
Vibration and thermal cycling can loosen the push-fit connector between the sensor harness and the PCB. Corrosion inside the plug can raise contact resistance enough to mimic a failed sensor without the sensor itself being defective.
- PCB fault Rare
If the sensor and wiring both test within specification, the signal-processing circuitry on the PCB may have failed. This is less common but should be considered once all other causes have been ruled out by an engineer.
How to fix it
- Reset the boiler once or twice DIY safe
Press the boiler's reset button or cycle the on/off switch as described in your user manual. Wait a couple of minutes for the boiler to restart. If the E24 code clears and the boiler runs normally, monitor it over the next day or two. A one-off dropout can occur due to a momentary wiring glitch. If the fault returns within a short time, further investigation is needed and repeated resets will not resolve the underlying problem.
- Check that your boiler pressure is between 1 and 1.5 bar DIY safe
Low system pressure can contribute to overheating events that stress sensors. Look at the pressure gauge on the boiler front. If it reads below 1 bar, top up via the filling loop until it sits around 1–1.5 bar, then attempt another reset. Do not overfill above 2 bar.
- Have a Gas Safe engineer inspect and test the return NTC thermistor Gas Safe engineer
An engineer will use a multimeter to measure the sensor's resistance at a known temperature and compare it against the manufacturer's resistance-temperature curve. A reading significantly outside specification confirms sensor failure. The return sensor is a low-cost part (typically £15–£25) but accessing it correctly and safely inside the boiler, and ensuring the system is properly drained and refilled, requires a qualified engineer.
- Have the sensor wiring harness inspected and repaired if damaged Gas Safe engineer
The engineer should trace the wiring from the sensor body back to the PCB connector, looking for signs of chafing, heat damage, or corrosion inside the plug. Damaged sections should be repaired using appropriate heat-resistant connectors or a replacement harness, not standard household wire.
- Have the PCB connections and PCB itself assessed if sensor and wiring are sound Gas Safe engineer
If the sensor resistance and wiring continuity both test correctly, the fault lies further down the signal chain. The engineer will check the PCB header pins and, if necessary, assess whether the PCB requires replacement. Given the age and parts availability of some Ravenheat models, the engineer may also advise on whether a boiler replacement is the more economical route at this stage.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
E24 requires diagnosis and repair by a Gas Safe registered engineer. You can verify a contractor's registration at gassaferegister.co.uk. Describe the fault code clearly when booking so the engineer can bring the likely replacement parts on the first visit.
Parts you may need
- Return NTC thermistor (10kΩ type, Ravenheat compatible) · from £20
- Sensor wiring harness · from £35
- PCB (model-specific) · from £180
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £100–£280, depending on the underlying cause.
Frequently asked questions
Can I fix the Ravenheat E24 fault myself?
The reset and pressure checks described above are safe for a homeowner to try. However, testing, removing, and replacing the NTC thermistor or any wiring inside the boiler must be done by a Gas Safe registered engineer. Working inside a boiler without registration is illegal under UK gas safety regulations and could void your home insurance.
How much does it cost to fix a Ravenheat E24 fault in the UK?
For the most common repair — a Gas Safe engineer's call-out plus return sensor replacement — expect to pay roughly £100–£280 including parts and labour. If the PCB turns out to be the root cause, replacement boards for Ravenheat boilers can cost £150–£250 for the part alone, pushing the total higher. For boilers over ten years old where parts are becoming scarce, your engineer may suggest that a new boiler is better value than an expensive repair.
Why does my Ravenheat keep showing E24 after I reset it?
A fault that clears on reset but returns within hours or days usually points to a sensor that is borderline — its resistance is drifting in and out of the acceptable window as the boiler heats up and cools down. Limescale build-up around the sensor pocket is a common accelerator of this behaviour on older systems. The sensor will typically fail completely before long, so booking an engineer sooner rather than later avoids being left without heating unexpectedly.
Could a power flush fix my Ravenheat E24 error?
Not directly. A power flush removes sludge and scale from the system pipework and can improve overall flow rates, which reduces thermal stress on sensors over time. However, if the NTC thermistor is already damaged, the flush alone will not restore it. An engineer may recommend a power flush alongside sensor replacement, particularly if the system has not been flushed recently and there is evidence of heavy scaling around the sensor pocket.