Worcester Bosch E9 276 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch E9 276 fault code mean?
The E9 fault code indicates that the safety temperature limiter in your central heating flow circuit has tripped. The 276 sub-code specifically tells you that the flow temperature sensor recorded a reading above 95°C, prompting the boiler to shut itself down before any internal components are damaged. This is a protective lockout, not necessarily a catastrophic failure, but the underlying cause must be identified before the boiler is returned to normal operation. Worcester Bosch boilers pair the main E9 code with a numeric cause code on the display — the most common combinations are E9 219 (heat exchanger fault or overheating), E9 220 or E9 221 (faulty or incorrect-reading safety temperature limiter), and E9 276 (flow sensor temperature exceeding 95°C). All of these sit within the same E9 overheat family and are covered on this page.
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
- Poor circulation or sludge build-up in the system Common
When heating water cannot flow freely around the system, heat accumulates inside the boiler and the flow temperature climbs rapidly. Sludge, magnetite deposits, trapped air, or partially closed valves are all common culprits. This is the single most frequent root cause of an E9 276 lockout, particularly in older systems or those without a magnetic filter.
- Failing or seized circulation pump Common
If the pump is struggling, running slowly, or has seized entirely, hot water produced in the heat exchanger cannot be moved away quickly enough. The resulting heat build-up triggers the safety limiter. A pump that is noisy, warm to the touch on the casing, or completely silent when the boiler fires is a strong indicator.
- Low system pressure Common
A sealed central heating circuit needs enough water in it to absorb and carry heat away effectively. When pressure drops below around 1 bar, the reduced volume of water heats up more quickly, and the limiter can trip. This is one of the easier causes to check and rule out yourself.
- Scaled or partially blocked heat exchanger (E9 219) Sometimes
Limescale accumulation — especially in hard-water areas — coats the internal surfaces of the heat exchanger, insulating the water from proper heat transfer and causing localised overheating. If your display shows E9 219 alongside 276, the heat exchanger is the primary suspect. Older boilers without inline filters are particularly vulnerable.
- Faulty safety temperature limiter or flow sensor (E9 220 / E9 221) Sometimes
Sometimes the boiler is not actually overheating at all — the limiter or its associated sensor has developed a fault and is reporting inflated temperature readings to the PCB. Cause codes 220 or 221 alongside E9 point here. The limiter then triggers a spurious lockout even under normal operating conditions.
- Faulty PCB Rare
A damaged or failing printed circuit board can misinterpret signals from perfectly healthy sensors, producing an E9 fault even when no real overheat event has occurred. This is harder to diagnose because it can mimic other causes and may also generate misleading cause codes. It is one of the less common and more costly explanations.
How to fix it
- Check the system pressure gauge DIY safe
Look at the pressure gauge on the boiler (usually visible through the front panel). It should read between 1.0 and 1.5 bar when the system is cold. If it is below 1 bar, the low water volume may be contributing to the overheat. Top up slowly via the filling loop — a braided flexible hose connected between two valves beneath the boiler — until the gauge reaches around 1.2 bar, then close both valves securely.
- Attempt a single reset DIY safe
Once pressure is confirmed to be correct, press and hold the reset button (marked with a flame and a cross symbol on most Worcester Bosch models) for around 3 seconds. The boiler should attempt to restart. If E9 276 returns within a short time, do not keep resetting — repeated resets on an overheat fault can mask a worsening underlying problem and should be avoided.
- Check that the gas supply is available DIY safe
Confirm that other gas appliances in the property (hob, oven) are working normally. If they are not, contact your gas supplier rather than attempting anything further with the boiler. If the gas supply is fine, this rules out a simple supply interruption as a contributing factor.
- Have a Gas Safe engineer inspect the circulation pump Gas Safe engineer
A registered engineer will check whether the pump is running at the correct speed, drawing the right current, and moving water effectively around the system. A seized or weak pump is one of the most common causes of E9 276 and will need professional assessment, repair, or replacement.
- Have a Gas Safe engineer inspect and test the safety temperature limiter and flow sensor Gas Safe engineer
If the display showed E9 220 or E9 221, the limiter or sensor itself may be sending incorrect readings. The engineer will test resistance and continuity, and if the component is confirmed faulty, replace it. Replacement is always preferred over repair for safety-critical sensors.
- Have a Gas Safe engineer carry out a powerflush or chemical flush if sludge or scale is suspected Gas Safe engineer
Where circulation is poor and the system has no magnetic filter or inhibitor, a powerflush forces clean water and descaling chemicals through the pipework and radiators at high velocity. After flushing, the engineer should dose the system with a corrosion inhibitor and fit a magnetic filter to prevent recurrence. In hard-water areas, a limescale reducer at the cold-water inlet is also worth considering.
- Have a Gas Safe engineer assess the heat exchanger if E9 219 was displayed Gas Safe engineer
A heavily scaled or cracked heat exchanger will require either descaling or full replacement. The engineer will advise based on the extent of the damage and the age of the boiler. On an older boiler, the cost of a heat exchanger replacement may prompt a broader conversation about whether a new boiler is the better investment.
- Have a Gas Safe engineer test the PCB if no other cause is found Gas Safe engineer
If all sensors, the pump, circulation, and heat exchanger check out, the PCB becomes the next investigation. PCB diagnosis requires specialist tools and knowledge. Replacement is expensive, so a good engineer will exhaust other possibilities first and may seek a second opinion before recommending it.
- Call a Gas Safe registered engineer if E9 276 persists or returns after a reset Gas Safe engineer
If the fault reappears after your initial reset and pressure check, do not attempt further resets or any internal investigation yourself. Contact a Gas Safe registered engineer to carry out a full diagnostic. You can verify an engineer's registration at gassaferegister.co.uk.
Parts you may need
- Circulation pump (compatible replacement) · from £85
- Safety temperature limiter / overheat thermostat · from £45
- CH flow temperature sensor · from £30
- Magnetic system filter (e.g. Adey MagnaClean or equivalent) · from £70
- Central heating inhibitor (1 litre) · from £15
- PCB (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 £150–£450, depending on the underlying cause.
Frequently asked questions
Can I just keep resetting the boiler to clear the E9 276 fault?
One reset after checking and correcting the system pressure is reasonable, but you should not repeatedly reset an overheat lockout. The boiler is shutting down because it detected a dangerously high flow temperature — resetting without finding the cause means it is likely to trip again, and in the worst case you could be masking a worsening problem such as a failing pump or a scaling heat exchanger. If it comes back after a single reset, call a Gas Safe registered engineer.
What is the difference between E9 219, E9 220, E9 221, and E9 276?
These are all sub-codes within the same E9 overheat family. E9 276 means the flow temperature sensor read above 95°C. E9 219 points toward the heat exchanger as the source of the overheating — often due to limescale build-up. E9 220 and E9 221 suggest the safety temperature limiter itself is faulty and may be reporting incorrect temperatures rather than an actual overheat occurring. All four require a Gas Safe engineer to diagnose fully, but knowing the sub-code helps the engineer narrow down where to start.
How much does it typically cost to fix an E9 276 fault in the UK?
Most people with an E9 276 fault pay somewhere between £150 and £450 for the repair, covering engineer call-out, diagnosis, and the most common fixes such as a pump replacement, limiter swap, or a system flush. If the heat exchanger needs replacing, costs typically run to £350–£620 including labour. A PCB replacement is the priciest common outcome at roughly £430–£780. If your boiler is over ten years old and needs either of those major components, it is worth asking the engineer whether a new boiler would be a more cost-effective long-term choice.
Could low boiler pressure really cause an E9 276 overheat fault?
Yes, though it is rarely the sole cause on its own. In a sealed central heating system, water is the medium that carries heat away from the heat exchanger. If the system pressure has dropped significantly — below around 1 bar — there is less water available to absorb that heat, so the flow temperature rises faster and the safety limiter can trip. Topping up the pressure to 1.0–1.5 bar via the filling loop and then resetting is always a sensible first step, but if E9 276 returns, a deeper issue such as poor circulation or a pump fault is almost certainly involved.