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How to bleed an oil boiler after running out of oil

Posted on: 28 May 2025
How to bleed an oil boiler after running out of oil

A Step-by-Step Guide

Running out of home heating oil is never ideal — especially in Northern Ireland’s colder months. Even after refilling your oil tank, your boiler might not fire back up straight away. That’s because it likely needs to be bled.

In this guide, we walk you through how to safely and effectively bleed your oil boiler if it’s gone into lockout mode.

⚠️ Caution: Bleeding a boiler involves working with pressurised fuel. If you’re unsure or uncomfortable at any point, call a professional. solv’s experienced engineers are just a phone call away.

Step 1: Confirm Your Boiler Needs Bled

When an oil boiler runs dry, it draws air into the fuel line. After your oil tank is refilled,boiler lock out light

this trapped air prevents the boiler from firing up. Signs your boiler needs to be bled include:

  • The red lockout light is on

  • You’ve pressed the reset button but nothing happens

  • You can hear the boiler trying to start but it fails to ignite

 

Step 2: Gather Your Tools

bleeding oil boiler tools

Before you start, make sure you have the following:

  • Rubber gloves – it can get messy

  • Plenty of rags – to catch any oil

  • Allen key – typically needed to access the bleed nipple

  • Confidence – this isn’t a job for the faint-hearted!

💡 Top Tip: Wear old clothes — oil splashes can ruin fabric.

bleed nipple on oil boiler

Step 3: Access the Fuel Pump

  1. Remove the front cover of your boiler using a screwdriver or appropriate tool.

  2. Locate the fuel pump — this is usually a small box with pipes running in and out of it.

  3. Find the bleed nipple — a small screw or bolt on the pump used to release air.

Step 4: Bleed the Boiler

bleeding oil boiler

  1. Place a rag under the bleed nipple to catch any oil.

  2. Insert your Allen key into the nipple and slightly loosen it — do NOT fully remove it.

  3. Press the reset button on the boiler.

  4. As the boiler attempts to fire, air will hiss out, followed by bubbling fuel.

  5. Once the air clears and you see a steady flow of oil, tighten the bleed nipple firmly.

⚠️ Never fully remove the bleed screw. Pressurised oil can spray out forcefully and cause damage or injury.

cleaning around oil boiler

Step 5: Final Checks

  • Check for any leaks around the bleed screw and fuel pump.

  • Clean up any spilled oil with rags.

  • Replace the boiler cover.

  • Turn the boiler back on and confirm it’s running normally.

Troubleshooting

  • If it doesn’t fire on the first attempt, try bleeding again — sometimes it takes two or three tries but don’t try this more than a handful of times, otherwise you could cause damage to internal parts of the boiler.

  • Still no luck? Call in the professionals at solv on 02890 451010. There could be a deeper issue that requires expert attention.

Need Help? Call solv.

Whether you’re DIY-savvy or would prefer to leave it to the experts, solv is here to help. We provide fast, efficient boiler servicing, repairs, and installations across Northern Ireland — based right here in Belfast.

📞 Call us: 02890 451010
🌐 Book online: www.solvgroup.com

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