How to Top Up your Boiler Pressure

Look underneath your boiler casing. Most UK households will have one of these three common setups:

• The Braided Hose (External): A flexible silver mesh pipe connecting two copper pipes, featuring a small tap or lever at each end.
• Lever (Keyless) These are often blue, white or black: Often found on modern models. This is a single lever tucked underneath that you simply pull down.
• The Internal Key: A plastic “key” that must be slotted into a specific port on the bottom of the boiler and turned to engage.

Safety First: Ensure the heating is turned off and the system has cooled down before you begin.

1. Open the valves: If using the silver braided hose, turn both small levers so they are in line with the pipe. You should hear the sound of rushing water entering the system.
2. Watch the gauge: Keep your eyes fixed on the pressure dial (or digital display) on the front of your boiler.
3. Target 1.5 bar: As the needle moves, wait until it reaches roughly 1.2 to 1.5 bar.
4. Close the valves: Quickly turn the levers back to their original position (usually at a right angle/perpendicular to the pipe) to stop the flow.

Warning: Do not get distracted! If you overfill the system (above 2.5 or 3.0 bar), you will have to go back to a radiator and bleed out water to manually lower the pressure.

• Check for leaks: Ensure the filling loop taps are fully closed and not dripping. If you used an external hose, some engineers recommend disconnecting it (keep a cloth handy for the small amount of water left in the hose).
• Power on: Turn your heating back on. It is normal for the pressure to rise slightly as the water expands while heating up.
• Monitor: If the pressure drops back to zero within a few days, you likely have a leak. Check your radiator valves and visible pipework for damp patches.

Always refer to your specific manufacturer’s manual for model-specific instructions.

If “turning the taps” isn’t solving the problem, or the problem keeps coming back, it’s time to call for backup.

• Frequent Pressure Loss: If you find yourself topping it up every few days or weeks, there is a leak somewhere. Constant fresh water introduces oxygen and minerals that corrode your system from the inside out.
• Visible Leaks: If you see water dripping from the boiler casing or any visible pipework.
• The Pressure “Rollercoaster”: If the pressure is low when cold but shoots up into the red zone (above 2.5 or 3 bar) when the heating is on, your expansion vessel has likely failed or lost its charge.
• Error Codes: If the boiler is locking out with a specific fault code (e.g., F22, E119, or F75) and won’t restart after a top-up.
• Dripping External Pipe: If the small copper pipe on your outside wall (the Pressure Relief Valve) is constantly dripping water.