Intergas F002 Fault Code: Causes, Fixes & Repair Costs
What does the Intergas F002 fault code mean?
The F002 code appears when your Intergas boiler detects that the water temperature inside the heat exchanger has climbed beyond its safe operating limit specifically while producing domestic hot water (DHW) — for example, when a tap or shower is running. As a safety measure, the boiler locks itself out and the fault code flashes on the display until the underlying problem is resolved. Importantly, the boiler cannot be reset while a component is still reading outside its acceptable range, so pressing the reset button without fixing the root cause will not clear the fault. F002 is part of the Intergas F-series overtemperature codes (F000–F006), each targeting a different operating mode or sensor; F002 specifically implicates the DHW circuit and its associated sensor (S3).
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 Incorrectly Wired DHW Temperature Sensor (S3) Common
The domestic hot water sensor S3 monitors water temperature in the DHW circuit. If its wiring is loose, corroded, or the sensor itself has drifted out of specification, it can report a false overtemperature condition even when the actual water temperature is perfectly safe. Intergas engineer guidance specifically calls out checking S3 wiring integrity and measuring sensor resistance before replacing it.
- Circulation Pump Failure or Reduced Flow Common
A pump that is seized, partially blocked with heating sludge, or running with failed bearings cannot move water quickly enough through the heat exchanger. Heat builds up rapidly in the DHW circuit and the boiler shuts down to protect itself. A tell-tale sign is a pump that is hot to the touch whilst the flow pipework remains cool — the motor is working but water isn't actually moving.
- Air Locks in the System Common
Trapped air behaves like a physical blockage, preventing proper water circulation. During a hot water draw the heat exchanger can overheat quickly if flow is restricted by an airlock. If you find yourself topping up system pressure regularly, or if radiators have cold spots, air in the system is a strong suspect.
- Sludge or Limescale Restricting the Heat Exchanger Sometimes
In hard water areas (particularly southern England) limescale can coat the internal surfaces of the heat exchanger, dramatically reducing heat transfer and causing temperature spikes during DHW demand. Iron oxide sludge from ageing pipework has the same effect. Without a magnetic filter or scale reducer in place, this build-up accelerates over time.
- PCB Fault Misreading Sensor Data Rare
In rare cases the printed circuit board itself misinterprets signals from S3 or triggers a lockout incorrectly. This is usually only considered once the sensor, wiring, pump, and water quality have all been ruled out by an engineer.
How to fix it
- Do not repeatedly reset the boiler DIY safe
The reset function is intended to restart the boiler after a fault has been corrected — it is not a fix in itself. While you can attempt one reset by holding the flashing Service button for approximately two seconds, if the F002 code returns immediately or the boiler will not reset at all, stop and move on to the checks below. Repeated resets without addressing the cause can mask the problem and potentially cause further damage.
- Check your gas supply is working DIY safe
Confirm that other gas appliances in your home (hob, gas fire) are working normally. If there is no gas supply, contact your gas supplier rather than your boiler engineer.
- Check and top up boiler pressure if needed DIY safe
Look at the pressure gauge on the boiler fascia. For most Intergas combi boilers the cold system pressure should sit between 1.0 and 1.5 bar. If it has dropped below 1.0 bar, top it up using the filling loop until it reads around 1.2–1.3 bar, then attempt a single reset. Low pressure can contribute to poor circulation and overheating.
- Bleed your radiators to release trapped air DIY safe
Starting with the downstairs radiators and working upwards, use a radiator bleed key to release any trapped air from each radiator and towel rail. Have a cloth ready to catch water once air stops escaping. After bleeding, re-check and top up the system pressure if it has dropped, then attempt a single reset. If you release a significant volume of air, inform your engineer — the system may benefit from a professional bleed of the pump itself.
- Have a Gas Safe engineer inspect and test the DHW sensor S3 Gas Safe engineer
An engineer will check the wiring harness to S3 for signs of corrosion, loose connections, or damage, and will measure the sensor's resistance values against Intergas specification. If the sensor is outside tolerance it will be replaced. This is the most common single-component cause of F002 and is relatively straightforward to diagnose with the right tools.
- Have a Gas Safe engineer inspect the circulation pump Gas Safe engineer
The engineer will check whether the pump is circulating water effectively, bleed any air from the pump housing, and test motor operation. If the pump is seized or its bearings have failed it will need to be replaced. A sludge blockage in the pump volute may be cleared during servicing.
- Have a Gas Safe engineer assess the heat exchanger for scale or sludge Gas Safe engineer
If sensor and pump checks draw a blank, the engineer will assess water quality and inspect the heat exchanger for limescale or iron oxide sludge restriction. A powerflush or targeted descale treatment may be recommended. Fitting a magnetic system filter and, in hard water areas, an inline scale reducer will help prevent recurrence.
- If the fault persists, have the PCB investigated Gas Safe engineer
Once all of the above have been ruled out, the engineer may test the PCB for faults in the sensor input circuitry. PCB replacement is a last resort and should only be carried out by an Intergas-trained engineer to preserve warranty where applicable.
- Ask a Gas Safe registered engineer to perform the final reset Gas Safe engineer
Only after the root cause has been identified and corrected should the boiler be fully reset. The engineer will confirm the boiler fires correctly, the DHW temperature reads within normal parameters, and that the F002 code does not return under live hot water demand.
Parts you may need
- DHW Temperature Sensor S3 · from £35
- Circulation Pump (compatible replacement) · from £95
- Magnetic System Filter · from £65
- Inline Scale Reducer / Conditioner · from £45
- PCB (Printed Circuit Board) · 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–£350, depending on the underlying cause.
Frequently asked questions
Why won't my Intergas boiler reset after the F002 code?
Intergas boilers are designed so that a reset is only possible once the fault condition has cleared — meaning the component causing the overtemperature reading must return to within its acceptable range first. If the DHW sensor S3 is faulty, or the pump is not circulating water, the boiler will simply refuse to restart or will lock out again almost immediately. This is a safety feature, not a malfunction. An engineer needs to diagnose and fix the underlying cause before a successful reset is possible.
Can I fix Intergas F002 myself?
Homeowners can safely carry out a small number of checks: confirming the gas supply is on, topping up system pressure via the filling loop, bleeding radiators to release trapped air, and attempting a single reset. Beyond that, any work inside the boiler — testing or replacing the S3 sensor, servicing the pump, descaling the heat exchanger, or touching the PCB — must be carried out by a Gas Safe registered engineer. Attempting gas appliance work without Gas Safe registration is illegal in the UK and potentially dangerous.
How much does it typically cost to repair an Intergas F002 fault?
Most F002 repairs fall between £100 and £350 once you factor in the engineer call-out and the most common fixes: sensor replacement, pump servicing, or a system bleed and re-pressurise. A full pump replacement typically adds £150–£300 in parts and labour. A powerflush, if the system has significant sludge build-up, usually costs £300–£500 separately. In rare cases where a PCB is at fault, expect an additional £250–£450 for parts and labour — though this is uncommon for F002 and worth confirming with an Intergas-trained engineer before proceeding.
How do I prevent the F002 fault from coming back?
The two most effective preventative measures are an annual boiler service (typically £80–£120) and fitting a magnetic system filter to catch iron oxide sludge before it reaches the pump or heat exchanger. In hard water areas of England, an inline scale reducer or water conditioner on the cold feed is also strongly recommended by Intergas. Catching a worn sensor or early pump strain at a routine service is far cheaper than dealing with a breakdown — and keeping your Intergas warranty valid usually requires annual servicing by a qualified engineer.