What it means
Shown on the Greenstar 4000 and the Worcester 2000.
What to check, in order
- Check the pressure gauge
Worcester's manuals say to top up below 0.8 bar on the Greenstar 4000 and below 1 bar on the Worcester 2000.
- Top up to 1 to 1.5 bar
Using the filling loop, as your user instructions describe.
- Bleed radiators only with the boiler off
If there's air in the radiators, turn the boiler off before you bleed them.
When to call a Gas Safe engineer
If it keeps happening, call a Gas Safe registered engineer. Worcester lists air locks, closed valves, a pump that isn't working, a sensor not touching its pipe and a faulty wiring harness.
Parts people end up buying
Only if the checks above point to a part. Match it to your model number first: it's on a label on the data badge, usually under the boiler or behind the front cover.
- Radiator bleed keySearch on Amazon
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Quick answers
What does the Worcester Bosch 2964 fault code mean?
Not enough water is flowing through the boiler's heat exchanger. Worcester says poor or no circulation can cause it, including air trapped in the heat exchanger. Shown on the Greenstar 4000 and the Worcester 2000.
Can I fix Worcester Bosch 2964 myself?
Easy (about 20 minutes). Start with: check the pressure gauge; top up to 1 to 1.5 bar; bleed radiators only with the boiler off. If it keeps happening, call a Gas Safe registered engineer. Worcester lists air locks, closed valves, a pump that isn't working, a sensor not touching its pipe and a faulty wiring harness.
Is Worcester Bosch 2964 worth repairing?
Usually free. If it's low pressure, topping up clears it. A pump or valve problem needs an engineer.
Checked against
- Worcester Bosch installation and servicing instructions, document 6720891161 (PDF)
- Worcester Bosch Worcester 2000 installation and servicing instructions, document 6721814551 (PDF)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.