Topping up the pressure on your Worcester Bosch combination boiler using the internal filling link and key

We get a lot of customers calling us because they are unsure on how to top up the pressure on their new boiler using the internal filling link.


If the needle on the pressure gauge on your boiler has gone into the red or down to zero it means there is little or no pressure left in the heating system and it needs to be topped up ASAP. So here’s Gas Care Swansea’s guide to refilling your Worcester Bosch combination boiler through the internal filling link.

  • First you need to slide the under carriage out from beneath the boiler. this comes off pretty easily, just pull it towards you and it will eventually drop down.
  • You will see attached to the under carriage a white filling key. Take the key out from its holder.
  • Now you need to locate the filling manifold. look under the boiler and you will see a black plastic filling manifold with a plastic nut next to it.
  • When you have located the filling manifold you then need to insert the key. if you look closely at the manifold you will see two padlock symbols, one is locked and the other is unlocked. Now look at the key and you will notice that the edge of the key is shaped like an arrow. insert the key so the arrow is in line with the unlocked symbol. make sure you push the key all the way in then turn it clockwise to the locked symbol.
free plumbing tips and advice how to top up pressure on my worcester bosch combination combi condensing boiler
  •  Now the filling key is in the correct position you can start to fill the boiler. slowly turn the white (or it can be grey) plastic nut next to the filling manifold anticlockwise until you can here water flowing into the boiler, keeping an eye on the pressure gauge on the front of the boiler. when the pressure is at the desired level (1-1.5 Bar) close the nut, take the filling key out and replace the under carriage.


  • When removing the filling key you may get a little bit of water dropping out so its a good idea to have a cloth ready to wipe up any excess.
  • If you accidentally over pressurise the system don’t worry just vent a few of the upstairs radiators and this will bring the pressure back down.

Copyright 2014 GasCare Swansea. All rights reserved.