09/09/2025
To top up the pressure on a Worcester Bosch boiler, you usually need to add water to the central heating system using the filling loop. This is a standard task you can do yourself, as long as you’re comfortable. Here’s a step-by-step guide for most Worcester combi boilers:
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🔧 What You’ll Need:
• Access to your boiler and filling loop (usually found underneath the boiler).
• The boiler manual (optional but helpful — if you’re unsure, I can help identify your exact model).
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âś… Normal Boiler Pressure:
• 1.0 – 1.5 bar (when cold)
• If it’s below 1.0 bar, you’ll need to top it up.
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🔄 Step-by-Step: How to Top Up Boiler Pressure
🧰 Option 1: Built-in Keyed Filling Loop (common in newer Worcester boilers like the Greenstar)
1. Turn off the boiler and let it cool.
2. Locate the white plastic filling key — often stored in a slot underneath the boiler.
3. Insert the filling key into the keyhole under the boiler and twist it to lock (usually 90 degrees).
4. Turn the grey or black k**b (next to the key) anticlockwise slowly.
5. Watch the pressure gauge rise to 1.2–1.5 bar.
6. Once it reaches the correct pressure:
• Turn the valve clockwise to stop the water.
• Twist and remove the filling key.
7. Turn the boiler back on.
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🔧 Option 2: External Filling Loop with Two Taps (common in older models)
1. Turn off the boiler.
2. Locate the silver braided hose underneath the boiler — this is the filling loop.
3. Turn both black/blue taps on either end of the loop to open them.
4. Watch the pressure gauge — stop when it reaches 1.2–1.5 bar.
5. Close both taps tightly.
6. Turn the boiler back on.
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⚠️ Important Tips
• Don’t overfill. Above 2.0 bar (when cold) is too much.
• If you accidentally over-pressurize, you can bleed a radiator to release pressure.
• If pressure keeps dropping, there may be a leak or faulty pressure relief valve — contact a Gas Safe engineer.
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If you tell me your exact model (e.g., “Greenstar 30i”), I can give you the most accurate instructions.
Would you like help identifying your boiler model?
