Intergas 2 Fault Code: Causes, Fixes & Repair Costs
What does the Intergas 2 fault code mean?
Intergas fault code 2 appears when the boiler's control board detects that the two water temperature sensors — S1 (flow) and S2 (return) — are giving readings that don't match their expected positions. The S1 sensor sits at the top of the heat exchanger and monitors the temperature of water leaving the boiler, while S2 sits at the bottom and tracks the temperature of water returning from your radiators. When the PCB sees the return temperature reading higher than the flow temperature, or otherwise detects that the sensors appear to be the wrong way around, it raises fault code 2 and locks the boiler out as a safety precaution. This is almost always caused by the sensors being physically or electrically transposed, though wiring faults or a failed sensor can produce the same symptom.
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
- Sensors transposed after servicing or repair Common
The single most frequent trigger for fault code 2 is an engineer accidentally swapping the S1 and S2 connectors when reconnecting them after a service, repair, or heat exchanger replacement. Because the Intergas NTC sensor (part 200117) fits both the top and bottom positions on the heat exchanger, it is easy to reconnect them the wrong way around during reassembly.
- Loose, damaged, or corroded wiring connections Sometimes
Even if the sensors were correctly installed, deterioration of the cable loom or its connectors can cause intermittent or incorrect signals to reach the PCB. Corrosion at the connector pins, chafed wiring, or a partially dislodged plug can all result in the board misreading the sensor positions and triggering this fault.
- Failed S1 or S2 NTC sensor Sometimes
If one of the thermistors develops an internal fault — drifting out of its resistance range or failing entirely — the PCB can interpret the mismatched readings as the sensors being swapped. A multimeter check across the sensor terminals will reveal whether the resistance curve is within the expected tolerance for the water temperature present.
- PCB fault misinterpreting sensor signals Rare
In rare cases, the printed circuit board itself develops a fault on the sensor input circuit, causing it to misread signals that are actually correct. This is only likely after all wiring and sensor checks have come back normal, and would typically be confirmed by swapping a known-good sensor and seeing the fault persist.
How to fix it
- Attempt a single boiler reset DIY safe
On most Intergas models a flashing LED above the key symbol alongside the fault code indicates a lockout. Press and hold the key/reset button as described in your user guide to attempt a restart. Only do this once or twice — if the boiler locks out again immediately, a reset alone will not resolve the underlying problem and you should move on to the next steps.
- Check the boiler's recent service history DIY safe
Think back to whether the boiler was recently serviced, had a repair carried out, or had any components replaced. Fault code 2 appearing shortly after an engineer visit strongly suggests the S1 and S2 sensor connectors were accidentally swapped during reassembly. Note this down to tell the next engineer — it helps them go straight to the likely cause.
- Have a Gas Safe engineer inspect and verify the sensor wiring loom Gas Safe engineer
An engineer will open the boiler casing and check that the S1 connector is attached at the top of the heat exchanger and S2 at the bottom, as specified for the Intergas wiring layout. If they find the connectors are reversed, swapping them back is a quick fix that should clear the fault immediately.
- Have the engineer test S1 and S2 with a multimeter Gas Safe engineer
If the wiring is found to be correct, the engineer will measure the resistance of each NTC thermistor at the known water temperature and compare the readings against Intergas's resistance-temperature table. A sensor reading outside tolerance confirms it has failed and needs replacing, rather than just being wrongly connected.
- Replace the faulty sensor with a genuine Intergas part Gas Safe engineer
Intergas recommends using the genuine NTC sensor (part number 200117) for both the S1 and S2 positions. Using genuine parts helps protect any remaining manufacturer warranty on your boiler and ensures the sensor's resistance characteristics match what the PCB expects.
- Reset the boiler after repairs and confirm normal operation Gas Safe engineer
Once the engineer has corrected the wiring or fitted a replacement sensor, they will reset the boiler and monitor it through a full heating cycle to confirm the flow and return temperatures are reading correctly and that fault code 2 does not return.
- If the fault persists, have the PCB investigated Gas Safe engineer
Should the fault code 2 reappear after confirmed correct wiring and known-good sensors, the PCB's sensor input circuitry may be the culprit. A Gas Safe engineer with Intergas experience can advise on PCB testing or replacement. PCB replacement is a more significant cost, so engineers will typically rule out all other causes first.
Parts you may need
- Intergas NTC Temperature Sensor (part 200117) — fits S1 and S2 positions · from £30
- Intergas cable loom / wiring harness · from £45
- Intergas PCB (model-dependent) · from £280
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 fix Intergas fault code 2 myself by swapping the sensors back?
No — and it is important not to attempt this. Accessing the sensor connectors inside the boiler requires opening the casing and working on internal components, which must only be done by a Gas Safe registered engineer. The only safe homeowner action is a single reset attempt. If the fault returns, call an engineer. You can verify any engineer's Gas Safe registration at gassaferegister.co.uk using the number on the back of their ID card.
How much does it cost to fix fault code 2 on an Intergas boiler?
For most people, the repair falls between £100 and £250 in total. If the fix is simply reconnecting the sensors the right way around, you will mainly be paying the engineer's call-out and labour fee. If a sensor has actually failed, the genuine Intergas NTC sensor (part 200117) is relatively inexpensive — typically £15–£40 for the part — so the total bill remains modest. If the PCB turns out to be the root cause, costs rise considerably, often £350–£500 including labour, so engineers will always rule out simpler causes first.
Why does fault code 2 often appear straight after a service?
Intergas uses the same NTC sensor (part 200117) for both the S1 (flow) and S2 (return) positions on the heat exchanger, meaning the two connectors look identical and fit either location. During a service or repair the heat exchanger is often disconnected, and it is straightforward to reconnect the two sensor plugs the wrong way around by mistake. The boiler runs briefly, the PCB detects the temperature readings are back to front, and fault code 2 is triggered. The fix in this case is quick — the engineer simply swaps the connectors to their correct positions.
Will fault code 2 affect my Intergas warranty?
Intergas boilers typically come with a warranty ranging from 12 months up to 10 years depending on the model and registration. To keep the warranty valid, the boiler must be serviced annually by a qualified engineer and only genuine Intergas parts should be fitted. If the fault arose from incorrect work by an engineer, you may have recourse to them directly. Check your warranty documentation or contact Intergas UK for guidance specific to your model and installation date.