Worcester Bosch 2971 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch 2971 fault code mean?
Fault code 2971 (sometimes shown as 2971 B on the display) appears exclusively on the Worcester Bosch Greenstar 8000 range and signals a system pressure problem. The boiler has detected that the water pressure in the central heating circuit is outside the acceptable operating range — typically meaning pressure is too low for the boiler to run safely. Until the pressure is restored to the correct level, the boiler will lock out and stop heating. The Greenstar 8000 uses a purely numeric fault code system, so you will see '2971' rather than the alphanumeric codes (like EA or E9) found on older Worcester Bosch models. Check your pressure gauge first — if it reads below 1 bar, a straightforward top-up via the filling loop may be all that is needed.
General guidance only — not a substitute for professional advice. 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
- Low system water pressure Common
The most frequent trigger for this code. Heating systems lose small amounts of water over time through micro-leaks, radiator bleeding, or normal evaporation through the expansion vessel. When pressure drops below roughly 0.5–0.8 bar the Greenstar 8000 will lock out. Check the pressure gauge on the boiler — a cold system should sit between 1 and 1.5 bar.
- Air trapped in the heating circuit Common
Air pockets in radiators or pipework reduce the effective water volume in the system, which can cause the pressure sensor to read incorrectly or cause pressure to fluctuate. Bleeding radiators removes the air, which may temporarily drop the pressure further before stabilising — after which the system should be re-pressurised to 1.2 bar.
- Faulty pressure sensor or wiring Sometimes
If the system pressure gauge reads correctly (1–1.5 bar cold) but the 2971 fault keeps returning after a reset, the pressure sensor itself or the cable connecting it to the PCB may be defective. A faulty sensor can report an out-of-range pressure reading even when the actual circuit pressure is fine.
- Slow water leak on the system Sometimes
A visible or hidden drip on a radiator valve, pipe joint, or the boiler's internal components can cause a gradual pressure drop that triggers the fault repeatedly. If you find yourself topping up the system every few days or weeks, a leak is the most likely explanation.
- Waterlogged or failed expansion vessel Rare
The expansion vessel absorbs pressure changes as the system heats and cools. If the vessel's internal diaphragm has failed, pressure can swing dramatically during a heating cycle — potentially triggering the pressure fault even when cold pressure appears normal.
- Pressure relief valve (PRV) weeping Rare
A PRV that has partially lifted and is releasing small amounts of water will cause persistent pressure loss. You may notice a damp patch or a trickle of water from the PRV discharge pipe outside the property.
How to fix it
- Check the boiler pressure gauge DIY safe
Locate the pressure gauge on the front of the Greenstar 8000. A cold system should read between 1 and 1.5 bar. If the needle is below 1 bar (or in the red zone), low pressure is the likely cause and you can proceed to re-pressurise. If pressure looks normal, skip to the reset step.
- Bleed any radiators that feel cold at the top DIY safe
Turn off the boiler and allow the system to cool. Use a radiator bleed key to open the bleed valve on any radiators that have cold spots at the top — a sign of trapped air. Hold a cloth under the valve; close it as soon as water (not air) begins to escape. Bleeding may drop the system pressure slightly, so always re-check the gauge afterwards.
- Re-pressurise the system using the filling loop DIY safe
Locate the filling loop — a braided or plastic hose with one or two valves, usually beneath the boiler. Slowly open the valve(s) and watch the pressure gauge rise. Stop when it reaches 1.2 bar. Close the valve(s) fully before proceeding. Never over-pressurise above 1.5 bar cold. Consult the Greenstar 8000 user guide if you are unsure where the filling loop is.
- Reset the boiler and observe DIY safe
Once pressure is at 1.2 bar, press and hold the reset button (refer to your user guide for the exact location on your model) until the boiler attempts to restart. Allow a full heating cycle to complete and recheck the pressure. If the boiler runs normally and pressure holds, the fault is resolved. If the code returns within hours or days, a leak or component fault is likely.
- Check for visible leaks around the boiler and radiators DIY safe
Inspect all accessible pipework, radiator valve connections, and the area beneath the boiler for damp patches, corrosion staining, or dripping water. If you find a leak, do not attempt to repair it yourself — note the location and report it to your engineer.
- Do not repeat the reset more than two to three times DIY safe
If the fault code 2971 returns after two or three resets without a clear cause being resolved, continuing to reset is not safe practice and will not fix an underlying fault. Stop resetting and arrange a professional inspection.
- Call a Gas Safe registered engineer for diagnosis and repair Gas Safe engineer
If the fault persists after re-pressurising and resetting, a Gas Safe registered engineer must inspect the boiler. They will test the pressure sensor and its wiring harness, check for internal or external leaks, assess the expansion vessel charge pressure, and inspect the pressure relief valve. Sensor replacement, expansion vessel work, and any internal boiler repairs must only be carried out by a qualified engineer. If your Greenstar 8000 is within its warranty period (Worcester Bosch offer up to ten years on some models), contact Worcester Bosch directly on 0330 123 3366 before arranging a third-party repair, as warranty work may be covered at no cost.
Parts you may need
- System pressure sensor (Greenstar 8000 compatible) · from £25
- Pressure sensor wiring harness / cable · from £18
- Pressure relief valve (3 bar PRV) · from £22
- Expansion vessel (8–12 litre, compatible replacement) · from £55
- Filling loop assembly · from £20
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 £90–£300, depending on the underlying cause.
Frequently asked questions
Why does my Worcester Bosch Greenstar 8000 keep showing fault code 2971 after I top up the pressure?
If the 2971 fault returns within a few days of re-pressurising, there are two likely explanations. First, there is a slow leak somewhere on the system — check radiator valves, pipe joints, and the area under the boiler for damp patches. Second, the pressure sensor or its connecting cable may be faulty, causing the boiler to report a pressure problem even when actual pressure is correct. Either way, a Gas Safe registered engineer should inspect the boiler to identify and fix the root cause rather than repeatedly topping up.
Is fault code 2971 dangerous? Should I turn the boiler off?
The Greenstar 8000 will lock itself out automatically when it detects a pressure fault, so it will not run in an unsafe condition. Low water pressure itself is not immediately dangerous, but you should not attempt to override the lockout or keep resetting the boiler indefinitely. If you cannot resolve the fault by re-pressurising once and resetting, switch the boiler off and arrange an engineer visit. There is no need to evacuate or treat this as an emergency unless you also smell gas, notice unusual noises, or see water leaking heavily.
What pressure should my Worcester Bosch Greenstar 8000 be set to?
When the system is cold (i.e. the heating has been off for at least an hour), the pressure gauge should read between 1 and 1.5 bar — 1.2 bar is the ideal target. When the system heats up, pressure will rise naturally to around 1.5–2 bar, which is normal. If the gauge regularly climbs above 2.5–3 bar during operation, or if the pressure relief valve is discharging water, call an engineer as the expansion vessel may need attention.
Could the 2971 fault code mean I need a new PCB on my Greenstar 8000?
It is possible but uncommon. The 2971 code is primarily a pressure-circuit fault, and the vast majority of cases are resolved by re-pressurising the system, fixing a leak, or replacing the relatively inexpensive pressure sensor (typically £15–£30 for the part). PCB replacement is a worst-case scenario — usually only considered if an engineer has ruled out all other causes — and typically costs £250–£500 including labour. Always get a proper diagnosis before agreeing to a PCB replacement.