Ravenheat E23 Fault Code: Causes, Fixes & Repair Costs
What does the Ravenheat E23 fault code mean?
The E23 code on a Ravenheat boiler signals a problem with the flue sensor — the component responsible for monitoring the temperature of exhaust gases as they leave the appliance. When the boiler's control board receives a reading from this sensor that falls outside the expected range, or receives no signal at all, it shuts the boiler down as a precaution. In some Ravenheat models this circuit also incorporates a flue fusible link (a one-shot thermal safety device wired in series with the water pressure switch), which trips permanently if the flue reaches a dangerously high temperature. Whether the root cause is a physically damaged sensor, an electrical fault in the sensor circuit, or a genuine flue overheating event, the boiler will lock out and display E23 until the underlying problem is resolved.
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
- Damaged or failed flue sensor Common
The flue temperature sensor (thermistor) may have developed an open or short circuit, causing it to send an incorrect or absent signal to the PCB. Corrosion and general component wear are particularly common on Ravenheat appliances, and a faulty sensor is the single most frequent explanation for E23.
- Wiring fault between sensor and PCB Sometimes
Even if the sensor itself is intact, damaged, corroded, or loosely connected wiring in the sensor circuit can produce the same out-of-range signal that triggers E23. Intermittent faults that come and go are often a wiring clue rather than a sensor problem.
- Flue fusible link tripped due to genuine overheating Sometimes
Certain Ravenheat models include a flue fusible link — a non-resettable thermal cut-out. If the flue has been genuinely overheating (for example due to a blocked or restricted flue outlet), this device may have permanently opened the circuit. A tripped fusible link always warrants investigation into why the flue ran so hot, not just replacement of the link.
- Blocked or restricted flue Sometimes
A partial blockage of the flue — caused by bird nesting material, debris, or a damaged terminal — can reduce exhaust gas flow, causing heat to build up and trigger the flue sensor or fusible link at abnormal temperatures.
- PCB fault Rare
In rarer cases the control board itself misreads or fails to process the sensor signal correctly, generating a spurious E23. This is more likely on older appliances where the PCB has suffered heat or moisture exposure over many years.
How to fix it
- Reset the boiler once or twice using the reset button DIY safe
A single reset occasionally clears a transient sensor glitch. Press and hold the reset button as described in your user manual. If E23 returns immediately or after a short run, do not continue resetting — repeated lockouts suggest a genuine fault that needs investigation.
- Check that the gas supply to the property is working DIY safe
Confirm other gas appliances (hob, fire) are working normally and that your gas meter isolation valve is open. If there is no gas supply, contact your gas supplier rather than a boiler engineer.
- Visually inspect the flue terminal outside DIY safe
From outside the property, check that the flue outlet is not visibly blocked by debris, a bird's nest, or physical damage. Do not attempt to dismantle or probe the flue — if you spot a blockage, report it to your engineer.
- Call a Gas Safe registered engineer to test the flue sensor and its wiring Gas Safe engineer
An engineer will use a multimeter to check the sensor's resistance against the manufacturer's expected values and perform a continuity check on the wiring loom. If bypassing the sensor circuit clears the fault and resistance readings are out of specification, the sensor is confirmed faulty.
- Replace the flue sensor or flue fusible link if confirmed faulty Gas Safe engineer
Only a Gas Safe registered engineer should remove and replace the flue sensor or fusible link. On Ravenheat appliances Ravenheat themselves have historically been firm that these safety components must only be touched by qualified engineers. The engineer should also verify what caused any overheating before fitting a replacement fusible link.
- Inspect the flue system for blockages or restrictions Gas Safe engineer
If a new sensor still produces E23, or if a fusible link has tripped, the engineer should check the full flue run for obstructions, incorrect fall, or damage that could cause abnormal flue gas temperatures.
- Consider PCB assessment if all other components test satisfactory Gas Safe engineer
If the sensor, wiring, and flue all check out, the engineer may need to assess whether the PCB is misinterpreting the sensor signal. Given that Ravenheat ceased trading in 2025 and spare parts are increasingly scarce, always ask the engineer for a replacement boiler quote alongside any PCB repair quote.
Parts you may need
- Ravenheat flue temperature sensor / thermistor · from £25
- Ravenheat flue fusible link / thermal cut-out · from £18
- Sensor wiring harness / loom · from £30
- Ravenheat PCB (where available) · 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–£250, depending on the underlying cause.
Frequently asked questions
Can I reset the boiler myself when E23 appears?
You can try one or two resets using the boiler's reset button — occasionally a transient sensor glitch will clear this way. However, if E23 comes back after resetting, stop and call a Gas Safe engineer. Repeatedly resetting a locked-out boiler can mask a developing fault and is not a fix in itself.
How much does it cost to fix a Ravenheat E23 fault in the UK?
For the most common repair — diagnosing and replacing the flue sensor — most UK homeowners pay somewhere between £100 and £250 including parts and labour. Wiring repairs tend to sit towards the lower end of that range. If the PCB turns out to be the cause, costs can rise considerably (PCBs for Ravenheat boilers are increasingly hard to source now the company has ceased trading, and second-hand units are often the only option). In that situation a new boiler installation may be more economical.
Ravenheat has ceased trading — can I still get parts for my boiler?
Ravenheat Manufacturing Limited was dissolved in 2025 after its parent company entered voluntary winding-up. Spare parts are still available from some independent heating parts suppliers and online marketplaces, but stocks are dwindling. Common consumable parts such as sensors and fusible links are still findable, but larger items like PCBs and gas valves are increasingly scarce or only available second-hand. Before committing to an expensive repair on an older Ravenheat boiler, it is worth asking your engineer for a new boiler quote at the same time so you can compare.
What is a flue fusible link and why does it cause E23?
A flue fusible link is a one-shot thermal safety device fitted in the flue assembly on certain Ravenheat models. It is wired in series with the water pressure switch circuit, so if it opens — either because the flue genuinely overheated or because the link has aged and failed — the boiler locks out. Unlike a sensor, a fusible link cannot be reset; it must be replaced. Importantly, if a link has tripped due to real overheating, the engineer should investigate and resolve the root cause (such as a blocked flue) before fitting a new one.