How to Repressurise Worcester Boiler Pressure

Last updated on October 15th, 2024

When your Worcester boiler pressure drops too low, the boiler will stop working, which means you will have no heating or hot water. Repressurising a boiler is easy but very important to keep your central heating system running.

I have been repairing boilers and heating systems full-time for over a decade, and have probably come across every boiler pressure problem.

Worcester Boiler Pressure

The boiler pressure should be between 1 and 1.5 bar when the central heating is off and the radiators are cold. The pressure rises when the heating is on, so you will not get the proper reading until it has cooled down.

• If your pressure drops below 1 bar you should top it up
• If it is above 1.5 (when cold) you should release some pressure

Pressure Too Low

Your Worcester boiler will usually stop working when the pressure drops too low, typically around 0.5 bar, but they will sometimes keep working on 0.

Low pressure can be fixed easily by topping it up, if you have to keep topping the pressure up, you have a problem that needs to be fixed.

Boiler keeps losing pressure

If your Worcester boiler is losing pressure you will have a leak somewhere on your heating system, or the pressure relief valve is letting the water out. To find out which it is, you can tie a carrier bag to the end of the copper blow-off (overflow) pipe outside.

If your boiler has lost pressure again, you should check the bag to see if it’s wet, if it is, that means the pressure relief valve is letting the water out.

This is most likely an expansion vessel problem, if so, you will need to recharge the expansion vessel, or you’ll have to replace it if the diaphragm inside is split.

If the bag is dry after losing pressure, you must have a leak on the central heating system. This will need to be found and fixed. Leaks can be anywhere on the full central heating system, boiler, radiators, or pipework under the floor.

Boiler leaking water

A Worcester boiler leaking water is quite common as they have a few places they regularly leak from.

• Hot water flow turbine adaptor
• Left-hand flow block
• Right-hand block

These leaks tend to be on the hot water side of the boiler so they shouldn’t affect the boiler pressure.

Losing pressure but no leak

A leak is the most common cause of a boiler losing pressure, but it could also be caused by:

• An expansion vessel problem
• A pressure relief valve problem
• A filling loop problem
• Bleeding the radiators

How to Repressurise a Worcester Boiler

To repressurise a boiler, add more water (pressure) to your heating system from the cold water supply via a filling loop.

Repressurise with a key

Unfortunately, some idiot at Worcester Bosch thought it would be a good idea to use a key to repressurise their boilers. Thankfully modern Worcester boilers don’t use a key to increase the pressure anymore.

How to repressurise a Worcester boiler with a key:

1. Insert the white plastic key
2. Turn the white square plastic knob anti-clockwise (like a tap) to open the filling loop and let some water in
3. Keep turning the white plastic knob until you can hear the water
4. When the pressure has reached 1 to 1.5 bar close the valve
5. Reset the boiler (if needed)
6. Turn the heating on

Repressurise without a key

To increase the pressure on a Worcester boiler without a key you will need to:

• Use (or fit) an external filling loop
• Use the new easy fill filling link on modern Worcester combi boilers

How to repressurise Worcester boiler without a key: (with external filling loop)

1. Open one valve fully (only if there are two valves)
2. Open the other valve slowly until you can hear the water
3. When the boiler pressure has reached 1 to 1.5 bar close both valves
4. Reset the boiler (if needed)
5. Turn the heating on

Do not open both filling loop valves fully straight away as the water pressure in the house might be too much for the boiler and cause the pressure to shoot up too much.

How often should you need to repressurise?

If you need to repressurise often, you have a problem that you need to get fixed. A boiler with a pressure gauge is a sealed pressurised system so you shouldn’t need to repressurise it at all. If the pressure keeps dropping, it means the water is getting out which should not be happening.

If you need to repressurise once or twice a year I wouldn’t worry about it as it’s such a small leak that it’s barely noticeable.

Pressure Too High

Having your Worcester boiler pressure too high (above 1.5 when the system is cold), means you will need to let some pressure (water) out of the system.

You can do this via a drain-off valve. A drain-off valve can be on the boiler, on a radiator valve or anywhere on the central heating pipework. Or, you can bleed water from a radiator from the bleed valve into a bucket. 

You will need to open the bleed valve with a bleed key and let the water out and into a bucket until the pressure has dropped back down.

How to release pressure

Knowing how to release pressure on a Worcester boiler might save you from some boiler problems. If you increase the pressure too much and cause it to go too high, you will need to release some pressure. There are a few ways to release the pressure on a Worcester boiler.

Here are my go-to ways when out on boiler repair jobs:

• Open a drain-off valve on the boiler or central heating system with a hose attached and let the pressure drop.
• Bleed a radiator from a bleed valve and let the water squirt out into a bucket. This can take a while for the pressure to drop.
• Crack a nut on the boiler heating pipes, or a radiator valve, and catch the water in a tub.
• Open the pressure relief valve on the boiler by pushing the red plastic lever.

Worcester Filling Loops

There should be one of these types of boiler filling loops under your boiler:

• A keyhole for a plastic key with a white square knob to turn: This knob will need turning like a tap to open and close.

• Easy-Fill filling link with blue handle: These are on the latest Worcester boilers (thankfully). This will simply need to be pulled down to top up and then released to stop filling.

• An external filling loop:

A filling loop will be built in on the bottom of your boiler on most modern and small combi boilers, but there could also be an external filling loop on the pipework.

Usually, this is below the boiler but there could be an external flexible filling loop anywhere on the heating system, sometimes hidden away in cupboards or behind boxing.

Expansion vessel undersized

Worcester boilers are sometimes undersized when fitted and are not large enough to cope with a large house’s central heating system. This means the expansion vessel might not be big enough and can cause problems with the pressure.

Getting the best combi boiler for a large house is very important, but adding an external expansion vessel that is large enough for the central heating system is also an option rather than upgrading to a bigger boiler.

Worcester boiler problems

Here are some other common Worcester boiler problems you can learn about:

• Worcester boiler not firing up
• Worcester boiler no hot water
• Worcester boiler timer replacement

Summary

It’s good to know what the problem is when your boiler is not working, but the first thing you need to check is the pressure gauge. If the pressure gauge is reading zero (or close to zero) your boiler needs to be repressurised to get it working.

Repressurising a Worcester boiler can be tricky with a key, but it can save you from having to pay a plumber to do it.

If you have to keep repressurising your boiler, you should get that problem found and fixed as soon as possible.

Feel free to ask any questions in the comments below, and I’ll do my best to help. If you found this post helpful, please consider sharing it.

FAQs

Can you repressurise a Worcester boiler by yourself?

Yes. You can repressurise a boiler by yourself, and you should learn how to repressurise a combi boiler if you don’t already know. Some boilers can be tricky to repressurise but most are very simple.

What causes a Worcester boiler to lose pressure?

There are many causes for a Worcester boiler to lose pressure. The most common cause is a leak, this could be on the boiler or anywhere on the central heating system.

Another cause could be the expansion vessel has lost its air and needs to be recharged or replaced. The pressure relief valve could also be letting by. Or, the filling loop on the Worcester boiler could be slightly open or damaged.

Do I need to turn my boiler off to repressurise?

No, you do need to turn your boiler off to repressurise. You should ensure the heating is turned off before repressurising the boiler as it will sometimes fire up as soon as it reaches the minimum working pressure. This can cause the pressure gauge to move around so you don’t get an accurate reading but it isn’t a big deal.