Intergas 23 Fault Code: Causes, Fixes & Repair Costs
What does the Intergas 23 fault code mean?
Fault code 23 on an Intergas boiler indicates a problem with the S2 sensor — the secondary NTC (Negative Temperature Coefficient) thermistor that monitors water temperature in the domestic hot water circuit within the boiler's combined heat exchanger. When the control board receives a reading from S2 that falls outside the expected range, or receives no signal at all, it triggers a lockout and displays code 23. You may notice the LED above the reset key flashing red alongside the code on the display. Fault codes 20 through 24 all relate to S2 sensor faults on Intergas HRE models, with code 23 typically pointing to an out-of-range or missing signal from that sensor. A single reset attempt is worth trying, but if the code returns promptly, the underlying fault needs diagnosing by a Gas Safe registered engineer.
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
- Failed or degraded S2 NTC sensor Common
The S2 thermistor itself has deteriorated or failed, producing resistance readings that the control board does not recognise as valid. This is the most common cause and is straightforward for an engineer to confirm with a multimeter check.
- Loose, corroded, or damaged sensor wiring Common
The wiring loom or connector between the S2 sensor and the PCB can suffer from corrosion, a loose terminal, or physical damage — all of which disrupt the signal and trigger the lockout. A visual inspection and continuity test will identify this quickly.
- Incorrectly seated or dislodged sensor Sometimes
If the boiler has been serviced recently, the S2 sensor may not have been refitted properly. Intergas specifically warns that failing to fit S1 and S2 sensors correctly can cause serious damage, so improper seating after a service is worth checking early.
- Limescale or sludge affecting the heat exchanger Sometimes
In hard water areas, limescale deposits on the heat exchanger can cause localised temperature spikes that skew S2 readings. Heavy sludge build-up can have a similar effect. This tends to occur in older systems that have not been chemically treated or regularly serviced.
- PCB (control board) fault Rare
If the S2 sensor and all associated wiring test within normal parameters, the PCB itself may be misinterpreting the signal. This is a less common but more costly cause, and an engineer will typically rule out everything else before condemning the board.
How to fix it
- Attempt a single boiler reset DIY safe
Press the reset button on the boiler's control panel. The red LED should stop flashing and the boiler will attempt to restart. If the boiler runs normally afterwards, monitor it closely. If code 23 reappears within a short time, do not keep resetting — the underlying fault needs professional attention.
- Check that your gas supply is working DIY safe
Confirm that other gas appliances in your home (hob, gas fire) are working normally. If your gas supply is interrupted, contact your gas supplier. This is unlikely to cause an S2 sensor code directly but rules out an obvious background issue before calling an engineer.
- Call a Gas Safe registered engineer to inspect the S2 sensor and wiring Gas Safe engineer
An engineer will use a multimeter to measure the resistance of the S2 NTC sensor across its operating temperature range and compare this against Intergas specifications. They will also inspect the sensor connector and wiring loom for corrosion, breaks, or loose terminals. This is not a task for an unregistered person.
- Engineer to replace the S2 NTC sensor if faulty Gas Safe engineer
If the sensor reads outside the expected resistance range, it will need replacing. Always insist on genuine Intergas spare parts — non-original components can affect performance and may invalidate any remaining warranty. Parts are guaranteed for one year when fitted by an authorised engineer.
- Engineer to inspect sensor seating and heat exchanger condition Gas Safe engineer
The engineer will confirm the sensor is properly located in its pocket on the heat exchanger. In hard water areas they may also assess limescale build-up and advise on a chemical descale or inhibitor dose to protect the system going forward.
- Engineer to test the PCB if sensor and wiring are both satisfactory Gas Safe engineer
Should the S2 sensor and wiring both check out as healthy, the control board may be at fault. PCB diagnosis and replacement is specialist work — the engineer may need to source a replacement board and reconfigure settings after fitting.
- If in doubt, contact Intergas directly for out-of-warranty support DIY safe
Intergas offer fixed-price out-of-warranty repairs that cover both labour and parts, with a one-year guarantee on workmanship and components. You can reach their service team at service@intergasheating.co.uk or on 01527 888000. Verify any engineer's Gas Safe registration at gassaferegister.co.uk before work begins.
Parts you may need
- Intergas S2 NTC temperature sensor · from £35
- Sensor wiring loom / connector · from £25
- Intergas PCB (control board) · from £220
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 £120–£320, depending on the underlying cause.
Frequently asked questions
Can I fix Intergas fault code 23 myself?
No. While you can safely attempt one reset and check your gas supply is on, the actual repair — testing the S2 sensor resistance, inspecting wiring, and replacing components — must be carried out by a Gas Safe registered engineer. Working on boiler internals without registration is illegal and dangerous.
What is the S2 sensor on an Intergas boiler?
The S2 sensor is a secondary NTC thermistor that sits on or within the heat exchanger and monitors the temperature of the domestic hot water circuit. It feeds live temperature data to the control board; if the signal is absent or out of range, the boiler shuts down and displays codes in the 20–24 range, with code 23 indicating a specific out-of-range or lost signal condition.
How much does it cost to fix Intergas fault code 23 in the UK?
For most people the repair falls between £120 and £320 all-in — this typically covers the call-out or diagnostic fee plus an S2 sensor replacement with labour. If the control board turns out to be the culprit, costs can rise considerably: a new PCB plus fitting can reach £400–£500 or more. It is worth checking whether your boiler is still under warranty before booking — Intergas offer a seven-year warranty on HRE and Xtreme models and ten years on the Xclusive range.
Will my Intergas warranty cover fault code 23?
It may do. Intergas warranty periods vary by range: ten years on the Eco RF and Xclusive, seven years on the Xtreme and HRE, six years on the Rapid Plus, and three years on the Rapid. To keep the warranty valid the boiler must have been serviced annually by a Gas Safe registered engineer. If your boiler is within warranty, contact Intergas directly on 01527 888000 before arranging a third-party repair.
Why does fault code 23 keep coming back after I reset it?
A reset clears the lockout but does nothing to fix the underlying problem. If the S2 sensor is failing, its wiring is intermittently breaking connection, or the PCB has a fault, the code will return — sometimes within minutes. Repeated resets without resolving the root cause can mask a worsening fault. Book an engineer if the code reappears after your first reset.