🔧 Plumber guide

How to repressurise a boiler

⏱ 5-10 minutes 📊 Difficulty: Easy 📅 Updated 2025

If your boiler pressure gauge reads below 1 bar, your heating and hot water won't work properly. Repressurising is a simple task — it involves opening a valve to let water into the system until the pressure reaches the correct level. No tools required.

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✓ Expert-written guide ✓ Difficulty: Easy ✓ Time: 5-10 minutes ✓ Professional plumbers available UK-wide

What you'll need

Filling loop (already attached to your boiler)
Boiler manual
⚠ Safety first

Never repressurise a hot boiler. If pressure keeps dropping repeatedly, there's a leak that needs professional attention — don't just keep adding water.

Step-by-step guide

  1. Check the pressure gauge
    Find the pressure gauge on the front of your boiler — it's usually a circular dial or digital readout. Normal operating pressure is between 1 and 1.5 bar. If it reads below 1, it needs repressurising.
  2. Turn the boiler off
    Switch the boiler off and let it cool completely. Adding water to a hot system can cause problems.
  3. Find the filling loop
    The filling loop is a short braided metal hose connecting the cold mains to the boiler, usually underneath the boiler unit. It has a valve (or two valves) that you open to let water in.
  4. Open the filling loop valve(s)
    Slowly open the valve(s) — usually by turning a lever to align with the pipe or turning a screw. You'll hear water entering the system.
  5. Watch the pressure gauge
    Keep watching the gauge as the pressure rises. Stop when it reaches 1.5 bar. Never go above 2 bar.
  6. Close the valve(s) firmly
    As soon as you hit 1.5 bar, close the filling loop valve(s). Leaving them open will over-pressurise the system.
  7. Restart the boiler
    Turn the boiler back on. The pressure should hold and the heating should work normally.
💡 Pro tip

Take a photo of your boiler's pressure gauge and filling loop on a normal day so you have a reference point.

Expert tips for the best result

  • Every boiler's filling loop is slightly different — check your boiler manual if you can't find it
  • Pressure naturally drops very slowly over months — topping up once or twice a year is normal
  • If pressure drops weekly or daily, you have a leak in the system — this needs a plumber
  • The pressure relief valve (PRV) releases water if pressure gets too high — check outside for dripping pipes if you've over-pressurised
  • Some modern boilers have an internal filling loop with a keyway rather than a lever

When to call a professional plumber

If you can't find the filling loop, if pressure rises above 3 bar, if the pressure relief valve keeps discharging, or if the pressure drops again within a week.

We connect you with vetted local plumbers across the UK — fast response, free quotes, guaranteed work.

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Frequently asked questions

How difficult is how to repressurise a boiler for a beginner?

This guide is rated Easy. If your boiler pressure gauge reads below 1 bar, your heating and hot water won't work properly. Repressurising is a simple task — it involves opening a valve to let water into the system until the pr If you're not confident, a professional plumber can do this quickly and provide a guarantee on the work.

How long does how to repressurise a boiler take?

Allow 5-10 minutes. This assumes the tools and materials are ready before you start. First-timers should budget extra time for preparation and any unexpected issues.

How much does a plumber charge for this in the UK?

Most plumbers charge £40-80 per hour depending on location and complexity. For a straightforward job like this, expect 1-2 hours of labour plus materials. Get a fixed quote via WhatsApp — message us with your postcode and job details.

How do I find a reliable plumber near me?

WhatsApp us with your postcode and job description. We match you with a vetted local plumber from our network — most jobs get a response within the hour. Contact us here.