Simple explanations for plumbing problems

Low pressure on a Worcester boiler

The majority of central heating systems have a drop in water pressure over time. Normally they are set to between 1 and 1.5 when the radiators are cold.  Worcester boilers have a unique way of filling that uses a plastic T shaped key in the bottom of the boiler. For people who don’t use it much it can be pretty hard to figure out.  This is a basic guide to filling up the boiler.

1. Check the pressure when the radiators are cold, the pointer will be between 1 and 0.


2. Take off the bottom cover. On modern Worcester boilers it slides forward. On older ones it clips off downwards.  The cover in the photo is a modern boiler.


3. Get the filling key out of the cover its supplied separately on older boilers and may be a bigger size. If the key is missing and there is no other method of filling your system a replacement key is available here. The hole it goes into can be on the left or right depending on the age of the boiler.

IMG_5090            IMG_5091

4. Line the arrow moulded into the body of the key upto the unlocked padlock moulded into the socket in the boiler.

IMG_5098            IMG_5092

5. Then push it in as far as it will go, its sometimes quite a tight fit so a bit of vaseline or soap on the black rubber o rings can help get it in far enough.  When its in as far as it will go turn it to the right so the arrow on the key is lined up with the locked padlock on the socket in the boiler.


6.  Now slowly turn the little square white knob to the left of the key. To open it turn it to the right until you can hear water flowing. Do this very slowly whilst keeping an eye on the pressure gauge. When it gets between 1 and 1.5 turn it back to the left  so the flow of water stops.


7.  That’s the pressure back to where it should be.  Now turn the key back to unlocked and pull it downwards and out.  You always get a little splash of water with the key as it comes out which is nothing to worry about. If it splashes then continues running/dripping the little white square knob might not be turned all the way off.  Put the key back in the cover and put the cover back on.  It generally hooks onto two runners either side then catches at the front.

« Fixing the problem

7 responses to “Low pressure on a Worcester boiler

  1. margaret watkins says:

    Hi I don’t have the key it’s a blue leaver but it’s a little stiff

  2. Beverley Ward says:

    hi there. Would you tell me what the model number is for the boiler illustrated above? I’m looking for a replacement bottom plate and the bottom front cover. Thank you so much

    • Graham says:

      It’s a standard cover for older Worcester boilers. I’ll have a look for a part number for you.

      • Beverley says:

        Lovely thank u. Can I send u pics of the two bits I’m looking for? I want to cover them as I’m afraid my 93 yr old mother and her carers will burn themselves etc. it’s the panel in your cover – i think and then the front panel that underneath panel fits to

      • Beverley says:

        did you see my question earlier? Would love to be able to send you pics of the two panels im looking for. b.

      • Beverley Ward says:

        Any luck?

        Sent from Beverley’s iphone


        div dir=”ltr”>


        blockquote type=”cite”>

      • Graham says:

        try this link:

        The bottom panels are all slightly different. You would have to provide a boiler model number or a gc (gas council number) number to get exactly the right model.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: