Simple explanations for plumbing problems

Low pressure on a Worcester boiler

Low pressure on a Worcester boiler is a special case and has been for quite a while.

For many years they have used a special filling loop with a white plastic key. This has caused many headaches for many people when topping up the pressure. The key can be confusing to use and has put many people off from filling the system up themselves if they aren’t confident. Great news for plumbers and boiler engineers. Not so good for your bank balance.

What is low pressure?

Most domestic boilers with a sealed system depend on a pressure of between 1 and 1.5 bar to operate properly.

In a perfect world the pressure would be set when the boiler was installed and never touched again.

In the real world however tiny leaks, bleeding radiators or faulty parts can cause the pressure to drop.

Click this link for more reasons the boiler pressure can go down.

Worcester pressure gauge showing the correct pressure.

Is low pressure a disaster?

Low pressure isn’t a disaster, it’s a pretty normal part of having a boiler with a sealed system.

If you are constantly topping up the pressure it’s a fault that has to be investigated and fixed but certainly not a disaster.

Most pressure drops are from tiny leaks on the radiators or boiler that can be easily repaired so no need to worry.

Worcester pressure gauge showing low pressure.

Where is my Worcester boiler filling loop?

This is the tricky bit with Worcester boilers.

There are three types of filling loops.

  1. External filling loop.
  2. Keyed filling loop.
  3. Keyless filling loop.
Advice on the types of filling loops from the official Worcester boilers website.
From the official Worcester boilers website


The simplest way to top up the pressure.

The caps should be removed and the hose should be reattached between the two valves. (Most of the time the hose is left on but it should be removed every time).

One valve is turned on either by the handle or a screwdriver.

The other valve is slowly opened until the pressure rises to between 1 and 1.5 bar.

Both valves are closed, the hose removed and the caps reattached.

A replacement filling loop kit can be bought from this link.

Advice on using an external filling loop is available on this link.

An external filling loop can be used to top up the pressure on a Worcester boiler.
An external filling loop


This method is more complicated and has been causing Worcester customers trouble for many years.

This video is the official Worcester guide on how the keyed filing loop works.

You can buy a replacement key from this link. New aware that there are two sizes so consider buying a pack of both to be sure.

From the official Worcester boilers website


This is Worcester finally getting it together and solving the problem of topping up the pressure.

The keyless kit turns filling the system up into a very simple job.

Pull down the blue handle to begin filling. The pressure gauge will slowly rise.

When the pressure gets to between 1 and 1.5 bar release the blue handle.

Replacement keyless kits are available from this link. It should be installed by a competent gas engineer.

From the official Worcester boilers website. How to use a keyless filling loop.
From the official Worcester boilers website

Follow this link for more advice on why your pressure is going down.

« Boiler faults

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


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      • 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.

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