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How do I re-pressurise my Worcester Bosch Boiler

This blog will explain how to fill your Worcester Bosch boiler using an Internal Filling Key.

The following boilers are included in this blog:

  • Worcester 24 CDi
  • 26 CDi Xtra
  • 28 CDi
  • 35 CDi II

If your boiler has a cover panel underneath, you will need to remove it. This can be done by dropping down the front and sliding it towards you.  The internal filling link assembly, if present, looks like a black moulding on the left of the boiler.

NB. some of the older models may use a larger key than the one pictured.  These larger keys look different in that they do not have any arrows on the shaft.   Please ignore references to the arrows if your key is different.

1) Make sure that the boiler is turned off and has cooled down.

2) Look up into the underneath of the boiler and to find a black plastic manifold.

3) Locate the white arrows (if present) engraved into the shaft of the T-shaped filling key and the padlock symbols on the outside of the manifold.

4) Place the key in the manifold and turn it to the right so it stops.  The arrow should now line up with the closed padlock symbol.

5) Rotate the white knob beside the manifold to the left, allowing the water to fill the system.   You should be able to hear this happening.  NB.  water will leak out of the manifold if the key is not properly connected.

6) Check the pressure on the pressure gauge.  When it reaches between 1 and 1.5 bar, it is time to turn the white knob back to the right to close the valve.  Be very careful not to over-tighten.

7) Turn the filling key to the left until the arrow lines up with the open padlock and remove the key.//

As a handy hint, remember to store the key behind the panel at the bottom of your boiler.

8) Note that, if you bleed your radiators, you might need to do this again.


Call My Plumber for a boiler engineer on 020 3078 5920 if you have any problems or email us on

How do I re-pressurise my Worcester Bosch Boiler

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