Intergas 10 Fault Code: Causes, Fixes & Repair Costs
What does the Intergas 10 fault code mean?
Fault code 10 on an Intergas boiler indicates that the PCB has detected a problem with the S1 sensor — the temperature sensor responsible for monitoring the flow of water leaving the heat exchanger. The PCB expects a continuous, plausible reading from this sensor; if the signal drops out entirely or falls outside acceptable limits, the boiler locks out and displays code 10. Worth noting: fault codes 10, 11, 12, 13, and 14 are all related to the heat exchanger sensor circuit. Codes 11–14 relate to the S2 return sensor and various out-of-range temperature conditions, but code 10 specifically points to an open or invalid signal from the S1 flow sensor. None of these codes can be permanently cleared by resetting alone — the underlying fault must be resolved first.
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 S1 flow sensor Common
The S1 sensor itself is the most frequent culprit. Over time, the sensor element can degrade, its resistance drifts outside the range the PCB expects, or an internal open-circuit develops. An engineer can confirm this quickly by measuring the sensor's resistance with a multimeter and comparing it to the manufacturer's specification.
- Limescale or sludge blockage restricting flow through the heat exchanger Common
If the sensor is electrically sound, the reading it is passing to the PCB may actually be accurate — meaning there is a genuine flow or temperature problem. Limescale deposits from hard-water minerals and magnetite sludge from corroding pipework and radiators can partially block the heat exchanger, reducing water flow to the point where the S1 sensor detects an abnormal temperature rise. A powerflush and installation of a magnetic filter and inhibitor typically resolves this.
- PCB fault or wiring issue Sometimes
Damaged wiring, corroded connector pins, or a failing PCB can cause the control board to misread or lose the signal from the S1 sensor entirely, even when the sensor itself is fine. An engineer will inspect the wiring loom and connector at the sensor, and test the PCB with a multimeter if no other cause is found.
How to fix it
- Check whether other gas appliances in your home are working DIY safe
Try a gas hob or check with your gas supplier to confirm there is no wider supply interruption. If you have a prepayment meter, ensure it has credit. A loss of gas supply will cause various fault codes and is nothing specific to the S1 sensor, but it is worth ruling out first.
- Note the exact fault code displayed and attempt a single boiler reset DIY safe
Locate the reset button on your Intergas boiler (typically a button on the front panel — consult your user manual for its position on your specific model). Press and hold for the time specified in your manual. If the boiler fires up and runs normally, monitor it over the next hour. If code 10 returns, do not keep resetting — repeated resets will not fix the underlying fault and may mask useful diagnostic information for your engineer.
- Inspect system pressure on the pressure gauge DIY safe
Check the pressure gauge on the boiler front. For most Intergas models, normal operating pressure when cold is around 1–1.5 bar. If it has dropped below 1 bar, top it up using the filling loop until it reads approximately 1.2–1.5 bar, then attempt one reset. Low pressure alone does not usually trigger fault code 10, but it can contribute to poor circulation.
- Arrange for a Gas Safe registered engineer to diagnose the fault Gas Safe engineer
All further investigation and repair must be carried out by a Gas Safe registered engineer. They will test the S1 sensor's resistance with a multimeter, inspect the wiring and connectors at the sensor, assess water flow through the heat exchanger, and check the PCB. Always verify the engineer's Gas Safe registration before work begins — you can do this at gassaferegister.co.uk.
- Engineer to replace the S1 sensor if faulty Gas Safe engineer
If testing confirms the S1 sensor has failed, the engineer will fit a genuine Intergas replacement part. It is important that original Intergas sensors are used and fitted correctly — incorrect or non-genuine sensors can cause further faults and may void any remaining warranty.
- Engineer to powerflush or chemically clean the system if blockage is suspected Gas Safe engineer
Where limescale or sludge is identified as the cause, the engineer will carry out a powerflush or targeted chemical clean using an appropriate descaler or system restorer. They should also fit a magnetic filter and dose the system with inhibitor fluid to protect against future contamination.
- Engineer to replace the PCB if all other causes have been eliminated Gas Safe engineer
If the sensor and wiring are sound and there is no circulation issue, the PCB itself may be misinterpreting the signal. PCB replacement is a last resort and is carried out entirely by the engineer.
Parts you may need
- Intergas S1 flow temperature sensor · from £50
- Magnetic system filter (e.g. Adey MagnaClean) · from £75
- Central heating inhibitor (e.g. Fernox F1, 1 litre) · from £15
- Intergas PCB (model-dependent) · from £250
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 £150–£380, depending on the underlying cause.
Frequently asked questions
Can I just keep resetting my Intergas boiler to clear fault code 10?
No — resetting will not fix fault code 10. The boiler locks out because the PCB has detected a genuine problem with the S1 sensor signal. Each time the boiler starts up without that signal being resolved, it will lock out again. Repeated resets may also obscure diagnostic information your engineer needs, so limit yourself to one reset attempt and then call a professional.
My Intergas boiler is still under warranty — am I covered for a fault code 10 repair?
Intergas boilers come with a standard 12-month warranty, and some models carry extended warranties of up to 10 years depending on the product and registration. Check your warranty documentation or contact Intergas UK directly before agreeing to pay for any parts. Even under warranty, the repair must still be carried out by a Gas Safe registered engineer.
What is the difference between fault codes 10, 11, 12, 13, and 14 on an Intergas boiler?
All five codes relate to the heat exchanger sensor circuit. Code 10 specifically indicates a fault with the S1 flow sensor — either an open circuit or an out-of-range reading. Codes 11 to 14 involve the S2 return sensor and various temperature limit conditions. In practice, codes 10–14 all point your engineer toward the heat exchanger sensor assembly, associated wiring, circulation, and the PCB as the areas to investigate.
Could fault code 10 mean I need a new heat exchanger?
In most cases, no. A new heat exchanger is only necessary if the unit is found to be physically cracked or severely corroded beyond cleaning. The far more common outcomes are a sensor replacement (around £50 for the part, plus labour) or a powerflush to clear a blockage. If a heat exchanger replacement does turn out to be needed, costs can rise significantly — in that scenario, it is worth getting a quote for a new boiler alongside the repair quote to compare the overall value.