How to Fix a Boiler Showing "Door" on the Display

May 13 2025 , 4 min reading time

If your boiler display shows the word "Door" and prevents it from running properly, there is a high chance that the boiler door switch is either stuck, misaligned, or damaged. This guide will help you troubleshoot and fix the issue, ensuring your boiler operates safely and efficiently.

If your boiler display shows the word "Door" and prevents it from running properly, there is a high chance that the boiler door switch is either stuck, misaligned, or damaged. This guide will help you troubleshoot and fix the issue, ensuring your boiler operates safely and efficiently.

What is a Boiler Door Switch and How Does it Work?

Most modern biomass boilers feature a limit switch near the combustion chamber door. This switch detects whether the door is properly closed by responding to pressure from the door itself. When working correctly, the door should press against the switch, activating an internal mechanism that signals the boiler to operate.

If the switch is faulty or misaligned, the boiler may incorrectly detect the door as open, preventing it from operating.

Common Causes and How to Fix Them

1. The Switch is Not Being Fully Pressed

Even if the door appears closed, it may not be pressing the switch enough to activate it.

✅ How to Check:

Open the boiler door and locate the switch.
Try pressing it manually – you should feel or hear a small click.
If you don’t, the switch may be stuck or broken.

🔧 How to Fix:

Adjust the position of the door or the switch to ensure they meet properly.
If the switch does not click even when pressed, it may need replacing.

2. The Switch or Cable is Damaged

If the switch or its wiring is damaged, the boiler won’t detect when the door is closed.

✅ How to Check:

Inspect the switch and surrounding wires for burn marks, cracks, or loose connections.
Consider if the boiler door was opened while the chamber was still hot – excessive heat can damage the switch or wiring.

🔧 How to Fix:

If the switch is visibly damaged, you’ll need to replace it.
You can buy a replacement boiler door switch here:
👉 Buy a new boiler door switch

3. The Switch is Stuck in the "Closed" Position

In some cases, the opposite issue occurs – the switch is permanently stuck in the closed position. This is a hidden fault that won’t always trigger the "Door" message but can cause dangerous problems.

✅ Why this is a problem:

The switch is meant to trigger the Induced Draft (ID) fan when the door opens, helping to vent heat and flames safely.
If the switch is stuck, the fan won’t activate, which could lead to overheating and safety risks.

🔧 How to Fix:

Carefully clean the switch to remove any debris that may be causing it to stick.
If the switch still won’t move, replace it immediately.

When to Replace the Boiler Door Switch

If adjusting or cleaning the switch doesn’t resolve the issue, the best solution is a replacement. A new switch ensures your boiler functions correctly and maintains essential safety features.

🛠 Get a new boiler door switch here:
👉 Order a replacement switch

Key Takeaways

✔️ If your boiler displays "Door", check the limit switch near the combustion chamber.
✔️ Ensure the switch is aligned properly and fully pressed when the door is closed.
✔️ Inspect the switch and wiring for damage or heat exposure.
✔️ If the switch is stuck, clean it or replace it to prevent hidden safety risks.
✔️ Order a new switch if the old one is faulty.