Worcester Bosch 2946 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch 2946 fault code mean?
Fault code 2946 (sometimes displayed as '2946 V') means the boiler's burner control unit has detected that the code plug fitted is either wrong for the model, corrupted, or missing entirely. The code plug is a small hardware component that acts like a configuration key — it tells the boiler's control board exactly which model it is and how it should operate. Without the right plug in place, the boiler locks itself out as a precaution and will not fire until the correct plug is fitted and the unit is reset. This is a locking fault, meaning a manual reset is required after the underlying problem is resolved. The 'V' suffix you may see on the display confirms this is a locking-type error rather than a temporary blocking fault.
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
- Wrong code plug fitted after a PCB or control board replacement Common
This is the most frequent trigger. When a PCB or burner control unit is swapped out during a repair, the engineer must transfer the original model-specific code plug across or fit the correct replacement. If the wrong plug — from a different model or revision — ends up installed, the boiler immediately raises fault 2946. Always worth checking if this fault appeared shortly after any recent boiler work.
- Code plug has failed or its data has become corrupted Sometimes
Even if the correct plug was originally fitted, the component can degrade over time or suffer a fault that causes it to lose its stored configuration data. The control unit then treats it as unrecognisable and locks out with a 2946 fault.
- Code plug dislodged or missing Sometimes
During servicing or other maintenance work inside the boiler casing, the code plug can occasionally be knocked loose or accidentally left out when the casing is refitted. If the control board detects no plug at all, it raises the same 2946 fault.
- Incompatible plug from a different model revision Rare
Worcester Bosch updates the code plug specification across product generations. A plug that was correct for an older revision of a model may not be recognised by a newer control unit, resulting in a 2946 lockout even though the plug is not physically damaged.
How to fix it
- Check whether any boiler work was carried out recently DIY safe
If a Gas Safe engineer visited to replace the PCB, control unit, or any major component shortly before this fault appeared, make a note of when and what was done. This information will help the attending engineer quickly identify whether an incorrect or missing code plug is the likely cause.
- Attempt a single boiler reset DIY safe
Locate the reset button on your boiler's control panel (usually a flame symbol with a line through it, or a dedicated reset button — check your user manual). Hold it for around 3 seconds. If the boiler fires up normally and stays running, monitor it closely. However, with a 2946 fault the lockout will almost certainly return immediately if the code plug issue has not been resolved, so do not reset more than two or three times.
- Do not open the boiler casing or attempt to locate the code plug yourself Gas Safe engineer
The code plug sits inside the boiler casing on or near the burner control unit. Opening the casing, touching internal components, or attempting to swap the plug yourself is unsafe, may void your warranty, and in any case requires identifying the exact correct part number for your specific model — something only a qualified engineer should do.
- Contact a Gas Safe registered engineer to diagnose and replace the code plug Gas Safe engineer
The engineer will confirm the fault, identify the correct code plug part number for your exact Worcester Bosch model and serial number, source the replacement, and fit it. Once the correct plug is in place the boiler is reset to clear the 2946 fault. This is typically a straightforward job that most engineers can complete in a single visit. Always verify the engineer is Gas Safe registered at gassaferegister.co.uk before booking.
Parts you may need
- Worcester Bosch model-specific code plug · from £25
- Burner control unit / PCB (if also found to be faulty) · 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–£200, depending on the underlying cause.
Frequently asked questions
Can I fix a Worcester Bosch 2946 fault myself?
No — and this is one fault where DIY is not an option even for practically minded homeowners. The code plug sits inside the boiler casing, and you would need to identify the exact part number for your specific model before sourcing a replacement. Opening the casing yourself is unsafe, risks invalidating your warranty, and is work that should only be carried out by a Gas Safe registered engineer. The good news is that this repair is usually on the cheaper end of the scale, typically £100–£200 all-in.
Why has my boiler developed a 2946 fault after a recent repair?
This is a very common scenario. If a PCB or burner control unit was replaced, the engineer should have transferred your original code plug across to the new board or sourced the correct replacement. If the wrong plug was fitted — or the plug was accidentally left out — the boiler will lock out with fault 2946 as soon as it detects the mismatch. Contact the engineer who carried out the work and explain what has happened; they should return to rectify it.
How much does it cost to fix a Worcester Bosch 2946 fault?
A code plug replacement is one of the less expensive Worcester Bosch repairs. The plug itself is a small component typically costing £10–£40 depending on the model. Add a Gas Safe engineer's callout and labour — usually around £50–£60 per hour — and most people pay £100–£200 all-in. This compares favourably with the average boiler repair cost of around £300 across all fault types. If a PCB replacement is also found to be needed, costs will be higher, but that is a separate issue from the code plug itself.
Will the 2946 fault come back once the code plug is replaced?
Once the correct, model-matched code plug is fitted and the boiler is reset, the 2946 fault should not return. If it does reappear shortly after the repair, it is worth asking the engineer to double-check that the plug supplied is genuinely the right part number for your exact boiler model and serial number, as even minor revision differences between models can cause incompatibility.