Intergas 13 Fault Code: Causes, Fixes & Repair Costs
What does the Intergas 13 fault code mean?
Fault code 13 on an Intergas boiler indicates a problem with the S1 sensor on the heat exchanger. Intergas boilers use two sensors on the heat exchanger — S1 monitors the flow side and S2 monitors the return — and fault codes 10 to 14 all relate to this sensor group. Code 13 specifically flags an issue with the S1 reading, meaning the boiler cannot confirm the heat exchanger is operating safely. As a result, the boiler will typically lock out and refuse to fire until the underlying problem is diagnosed and resolved, after which a reset is required to clear the code.
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 sensor Common
The S1 temperature sensor itself may have developed a fault — either giving a reading that is out of range or no signal at all. This is the most straightforward cause and the first thing an engineer will test when presented with code 13.
- Limescale build-up restricting circulation Common
In hard water areas, limescale accumulates inside the heat exchanger over time, restricting water flow and causing localised overheating near the S1 sensor. This is particularly common in older boilers or those that have never been power-flushed or had inhibitor added to the system.
- Wiring fault or poor connection to the S1 sensor Sometimes
Loose terminals, corroded connectors or damaged wiring between the S1 sensor and the PCB can produce erratic or absent signals, triggering the fault code even when the sensor itself is still functional.
- PCB failure Sometimes
If wiring and the sensor both test correctly, the PCB may be failing to process the S1 signal accurately. This is a less common but more expensive outcome, requiring board repair or full replacement.
- Cracked or blocked heat exchanger Rare
Physical damage to the heat exchanger, or a severe internal blockage from sludge or scale, can cause abnormal flow conditions that the S1 sensor detects as a fault. This is the most serious and costly outcome.
How to fix it
- Check whether your gas supply is working DIY safe
Before assuming the boiler has a component fault, confirm that other gas appliances in the property (such as a hob or gas fire) are working normally. If there is no gas supply, contact your gas supplier rather than a heating engineer.
- Attempt a single boiler reset DIY safe
Locate the reset button on your Intergas boiler (usually a dedicated button or a long-press of the mode button — refer to your user guide). Press and hold as instructed to attempt a reset. If the fault clears and the boiler runs normally, monitor it closely. If code 13 returns, do not keep resetting — repeated resets without fixing the root cause can mask a developing fault.
- Check system pressure DIY safe
Glance at the pressure gauge. Intergas boilers typically operate between 1.0 and 1.5 bar when cold. If pressure has dropped below 0.8 bar, top it up via the filling loop following your boiler's user guide. Low pressure alone is unlikely to cause code 13, but it is worth ruling out before calling an engineer.
- Call a Gas Safe registered engineer to test the S1 sensor Gas Safe engineer
An engineer will use a multimeter to check the resistance of the S1 sensor against the manufacturer's specification. A reading outside the expected range confirms sensor failure, and replacement is a straightforward repair that should restore normal operation.
- Have the engineer inspect for limescale and sludge Gas Safe engineer
If the sensor tests correctly, the engineer will assess the heat exchanger and system pipework for scale or sludge build-up. Depending on severity, this may mean descaling the heat exchanger, a full power-flush of the system, and dosing with inhibitor and limescale-reducing chemicals to prevent recurrence.
- Have the engineer check wiring and PCB Gas Safe engineer
If both the sensor and circulation are satisfactory, the engineer will trace the wiring loom from the S1 sensor to the PCB, looking for loose terminals, corrosion or damaged insulation. Any faulty wiring must be repaired or replaced. If the board itself is the cause, a PCB replacement will be needed.
- Discuss heat exchanger replacement or new boiler if required Gas Safe engineer
A cracked or severely blocked heat exchanger that cannot be cleaned may need replacing. Given the cost of a new heat exchanger, the engineer should help you weigh up repair versus replacement — particularly if the boiler is older or has multiple worn components. Always check whether your Intergas warranty (which can run from 1 to 10 years depending on the model and registration) covers the repair before authorising any paid work.
Parts you may need
- Intergas S1 flow temperature sensor · from £50
- Sensor wiring harness / connector · from £25
- Intergas PCB (printed circuit board) · from £220
- Heat exchanger (model-specific) · 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 £120–£380, depending on the underlying cause.
Frequently asked questions
Can I reset an Intergas fault code 13 myself?
You can try a single reset — the reset procedure is described in your Intergas user guide and is safe for a homeowner to perform. However, code 13 is a lockout caused by a genuine sensor or heat exchanger issue, so if the fault returns after one reset you should stop and call a Gas Safe engineer. Repeated resets without a fix will not resolve the underlying problem.
Is fault code 13 dangerous?
The boiler locking out is actually a safety mechanism working correctly — it has detected an abnormal condition at the heat exchanger and shut down to prevent damage or unsafe operation. The boiler will not produce heat while locked out, but there is no immediate danger to the household. Contact a Gas Safe engineer promptly, especially during cold weather.
How much does it cost to fix Intergas fault code 13?
Most repairs for this fault code fall between £120 and £380. A straightforward S1 sensor swap with a call-out is at the lower end, while a power-flush or PCB replacement will sit toward the top of that range. A heat exchanger replacement is more expensive — typically £400–£550 all-in — so if that is needed it may be worth comparing the cost of repair against a new boiler installation.
My Intergas boiler is still under warranty — will this be covered?
Intergas boilers come with at least a 12-month warranty as standard, and many models registered at installation carry a 3–10 year warranty. If your boiler is within its warranty period, contact Intergas or your installing engineer before arranging an independent repair, as unauthorised work may void the remaining cover. Have your installation date and model details to hand when you call.