Worcester Boiler Pressure: How to Repressurise a Greenstar

The right pressure for a Worcester boiler

Worcester Bosch's own guidance is that when the heating system is cool, the pressure gauge should read between 1 and 1.5 bar. Its Greenstar i troubleshooting page adds that the pressure should sit at around 1 bar with the heating off and will usually rise to 1.5 bar or more while the boiler is running. That rise is the water expanding as it heats, and it is normal.

Greenstar boilers show pressure either on a dial gauge under or on the front of the boiler, or as a number on the display, depending on the model. When the pressure falls too low, the boiler locks out and shows the low pressure code CE 207.

Where is the filling loop on a Worcester Greenstar?

On most Greenstar combis, the filling device is underneath the boiler. Worcester describes three set-ups, and you need to know which one you have before you start.

Keyless filling link

A blue lever under the boiler. Worcester sells the keyless filling link as an accessory for current models such as the Greenstar 4000, so many newer installations have one.

Internal filling loop with a filling key

A small removable key, usually clipped inside a hatch on the underside of the boiler. British Gas's guide describes finding the key clipped inside that hatch. Worcester's Greenstar i troubleshooting page lists this key and the keyless link as the two ways to top up that model.

External filling loop

A silver braided hose with a valve at each end, usually connected between two pipes under the boiler. System and heat-only boilers, such as a Greenstar used with a cylinder, often have this type, sometimes in the airing cupboard rather than under the boiler.

If you cannot tell which you have, check the user manual for your model. Some current models, including the Greenstar 4000, are also compatible with Worcester's Greenstar Intelligent Filling System, an automatic filling option.

How to repressurise a Worcester boiler

Before you begin, turn the boiler off and let the system cool, so you are reading the cold pressure. Have the gauge in view the whole time.

With a keyless filling link

1. Find the blue lever under the boiler.
2. Pull the lever down and hold it. You will hear water flowing.
3. Watch the gauge. Worcester's instruction is to release the lever once the pressure has risen to over one bar.
4. Release the lever fully so it springs back and seals.

With the internal filling key

1. Open the hatch under the boiler and unclip the filling key.
2. Insert it into the filling point. British Gas describes this as a small hole just to the right of a white square, then turning the key and the white square to let mains water in.
3. Watch the gauge rise. Worcester says to stop at just over one bar.
4. Turn the key back to the open padlock position and remove it, then put it back in its clip for next time.

With an external filling loop

1. Check the braided hose is connected at both ends.
2. Open the valve on the cold mains side, then slowly open the second valve that lets water into the heating system. Worcester's advice is to stop once the gauge reaches about one bar.
3. Close both valves fully.
4. If your installer has left the hose connected, it is good practice to disconnect it now, as the regulations expect the loop to be disconnected after use.

With the pressure back at 1 to 1.5 bar, turn the boiler back on and reset it if it still shows CE 207. Our general guide to boiler pressure too low has more on the filling process across other brands.

How to increase pressure on a Worcester boiler without the key

If your Greenstar uses a filling key and it has gone missing, do not try to turn the filling point with pliers or a screwdriver. It can break the plastic fitting and leave water running into the system. Your options are:

• Look properly for the key. It is often still clipped in the hatch under the boiler, or tucked into the boiler cupboard or a kitchen drawer with the manual.
• Buy a replacement. Filling keys and keyless filling links are available as Worcester spare parts. Quote the model and serial number from the data label, usually inside the front or underneath.
• Have a keyless link or external loop fitted. A heating engineer can fit Worcester's keyless filling link or an external loop, so you are not relying on a small loose part again.

Until then, the boiler will not run properly below its minimum pressure. If the house is cold and there is no way to top up, call an engineer rather than improvising.

Why a Worcester boiler keeps dropping pressure

Worcester says topping up once or twice a year is normal. If you are doing it much more often, contact an installer, because water is leaving the system somewhere. Worcester's Greenstar i troubleshooting advice is to check radiator valves and connections for leaks, and to look at the pressure relief valve pipe outside for dripping. The usual causes are:

• A small leak. Look for damp at radiator valves, pipe joints and under the boiler. Our guide to a boiler leaking water covers where to look.
• The pressure relief valve letting water out. A copper pipe runs from the boiler through the outside wall. If it drips, the valve is opening or no longer sealing.
• A flat expansion vessel. The pressure shoots up when hot, water escapes through the relief valve, then the pressure is low when cold. See our guide to the expansion vessel.
• Bleeding radiators. Every time air is let out, the pressure falls a little. After bleeding, always check the gauge. Our radiator bleeding guide explains why.

Worcester boiler pressure too high

If the gauge reads close to 3 bar, the pressure is too high. Worcester's installation manual for the Greenstar R 28 HE, for example, sets the pressure relief valve to open at 3 bar, which is the usual figure for domestic sealed systems, so water will start dripping from the outside pipe. The common causes are overfilling, a filling key or link left open, a filling valve that is letting water through, or a failed expansion vessel.

Check first that the filling key has been turned back to the closed padlock position or that the blue lever has sprung back. If the pressure is high with the system cold, you can bring it down by bleeding a radiator and letting out a little water until the gauge reads 1 to 1.5 bar. Our guide to boiler pressure too high goes through this step by step.

When a Worcester pressure problem needs an engineer

Topping up with the filling key, link or loop is a job Worcester expects owners to do. Call a Gas Safe registered engineer, or a Worcester accredited installer, if the pressure keeps dropping, the relief pipe drips, the pressure rises to near 3 bar when hot, the gauge does not move when you fill, or CE 207 stays on the display with the gauge reading correctly. That last one can mean a faulty pressure sensor.