Worcester Bosch 2920 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch 2920 fault code mean?
The 2920 is a cause code on Worcester Bosch boilers that points specifically to the heating circuit pump being blocked or seized. You will typically see it alongside the flow temperature reading, with the display flashing to indicate the pump fault. As a cause code, 2920 appears in the boiler's information menu (accessed by pressing the spanner/return button) rather than as a standalone display code — it gives you the detailed reason behind a broader blocking fault that has caused the boiler to shut down circulation. In plain terms: your boiler has detected that the pump is not moving water around the system as it should, so it has shut itself down as a safety measure.
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
- Seized or stuck pump impeller Common
This is the most frequent cause, particularly if the boiler has been idle for a long period — for example, after sitting unused through the summer months. The impeller (the rotating part inside the pump) can lock up due to scale or corrosion, preventing water from circulating. You may also notice a humming or vibrating noise near the pump when the boiler tries and fails to run it.
- Sludge and magnetite build-up Common
Over time, rust particles and magnetite sludge accumulate inside the system pipework and can coat or clog the pump impeller. This is more common in older systems that have never been flushed or do not have a magnetic filter fitted. Restricted impeller movement triggers the 2920 code.
- Airlock within the pump or pipework Sometimes
A pocket of trapped air in the pump housing can prevent the impeller from turning freely or stop water flow altogether. If you hear gurgling or bubbling sounds near the pump, an airlock is a strong possibility. Some pumps have a bleed screw that an engineer can use to release the trapped air.
- Pump motor failure Sometimes
The electric motor driving the pump can burn out or fail, especially in older units. If the pump body is notably hot to the touch but there is no water movement, the motor may have overheated or failed entirely. In most cases, the pump will need to be replaced rather than repaired.
- PCB or wiring fault Rare
If the pump itself is mechanically sound but still not running, the issue may lie with the printed circuit board or the wiring that controls it. A faulty PCB may fail to send the correct signal to the pump, or a damaged wiring connection may interrupt power to the motor entirely.
How to fix it
- Check the boiler pressure gauge DIY safe
Look at the pressure gauge on the front of the boiler. It should read between 1 and 1.5 bar when the system is cold. If it reads below 1 bar, top up the system using the filling loop until it reaches around 1.2 bar, then reset the boiler. Low pressure alone is unlikely to trigger 2920, but it can compound circulation problems.
- Try a single reset and observe DIY safe
Press the reset button on your boiler and allow it to restart. Watch whether it fires up and runs normally or returns to the fault quickly. Do not reset more than two or three times in total — repeated resets without fixing the underlying fault can cause further damage and will not resolve a genuinely blocked pump.
- Listen and feel for pump activity DIY safe
With the boiler attempting to run, carefully place your hand near (but not on) the pipework close to the pump. You should feel slight warmth and possibly vibration if the pump is running. A total absence of any movement or a loud humming with no warmth suggests the pump is seized. Report these observations to your engineer — it helps them diagnose faster.
- Contact a Gas Safe registered engineer to inspect and free the pump Gas Safe engineer
An engineer will access the pump, check whether the impeller can be freed (sometimes a careful, controlled technique can release a mildly seized pump), bleed any airlocks, and test the motor. They will advise whether the pump can be returned to reliable service or whether replacement is the better option. Attempting to open the boiler casing or interfere with the pump yourself is unsafe, could void your warranty, and is not permitted under UK gas safety regulations.
- Have the system power-flushed if sludge is identified Gas Safe engineer
If the engineer finds significant sludge or magnetite contamination, a power flush may be recommended to clear debris from the pipework and pump. This also extends the life of the new pump. Ask about fitting a magnetic filter (such as a Magnaclean) at the same time to protect against future build-up.
- Replace the pump if it cannot be reliably restored Gas Safe engineer
Where the pump motor has failed or the impeller is beyond recovery, the engineer will fit a replacement pump compatible with your specific Greenstar model. Replacement is generally the more reliable long-term solution compared with repeated attempts to revive an ageing pump.
Parts you may need
- Heating circuit pump (Grundfos or equivalent, boiler-specific) · from £120
- Pump bleed screw / seal kit · from £8
- Magnetic system filter (e.g. Magnaclean Pro2) · from £65
- PCB (if wiring/control fault confirmed) · from £220
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
Is the 2920 code the same as a locking fault — will the boiler stay off until it is repaired?
The 2920 is technically a cause code sitting behind a blocking fault, which means the boiler shuts down circulation but may attempt to restart. However, if the pump remains unable to move water, the boiler will continue to fault and eventually lock out. You should treat it as an urgent fault and arrange an engineer promptly rather than repeatedly resetting in the hope it clears on its own.
Can I unblock the pump myself?
No. Accessing the pump requires opening the boiler casing, which must only be done by a Gas Safe registered engineer. Attempting it yourself is unsafe, is likely to invalidate your boiler's warranty, and in the case of a boiler still under guarantee could also void your cover. The only checks a homeowner should carry out are those described in the troubleshooting steps above.
How much does it cost to replace the pump on a Worcester Bosch boiler?
Most homeowners pay between £150 and £380 for a pump replacement on a Worcester Bosch boiler, covering parts and labour. The pump itself typically costs £90–£200 depending on the model, with labour on top. If you use Worcester Bosch's own out-of-guarantee repair service, their fixed-price repairs start from around £381 inc. VAT. Costs at the higher end tend to reflect London and South East labour rates or sourcing difficulties for older models. If it turns out the PCB has also failed, that can add a further £200–£350 to the job — worth discussing with your engineer before authorising work.
Why has my pump seized? The boiler was working fine until recently.
Pump seizure over summer is extremely common: when a boiler sits unused for months with no water flowing, the impeller can corrode or scale up in place. Running a brief boiler test in spring and autumn — even just for 10–15 minutes — helps keep the pump moving and dramatically reduces the risk of seizure. Magnetite sludge from ageing pipework is another common cause; fitting a magnetic filter and arranging an annual service are the best ways to prevent a recurrence.