---
title: "Boiler Fault Codes Explained: When to Call an Engineer"
description: Boiler fault codes explained by Trusted Boilers Ltd. Learn what common boiler error codes mean, when you can reset, and when to call a Gas Safe engineer in South London and North Surrey.
image: https://www.trustedboiler.co.uk/hubfs/20251118_190222.jpg
---
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# [Boiler Fault Codes Explained: What They Mean and When to Call an Engineer](https://www.trustedboiler.co.uk/blog/boiler-fault-codes)
[](https://www.trustedboiler.co.uk/blog/author/trusted-boilers-ltd)
by [Trusted Boilers Ltd](https://www.trustedboiler.co.uk/blog/author/trusted-boilers-ltd)
4 min read
Nov 18, 2025, 8:54:28 PM
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Modern boilers are clever pieces of equipment. When something goes wrong, they often display a **fault code** to help identify the problem. The challenge for most homeowners is simple: the code appears, the heating stops, and the screen might as well be in another language.
In this guide, Trusted Boilers Ltd. explains what boiler fault codes are, what some of the most common ones mean, and when you can safely try a reset – and when you should call a **Gas Safe registered engineer**.
If you’re currently without heating or hot water, you can [book a boiler repair](https://www.trustedboiler.co.uk/boiler-repairs) with Trusted Boilers in South London and North Surrey.
## What Are Boiler Fault Codes?
Boiler fault codes are short alphanumeric messages (for example, “F22” or “EA”) shown on your boiler’s display when the appliance detects a problem.
They help to:
- Protect the boiler from damage
- Keep you and your property safe
- Speed up diagnosis for an engineer
Each manufacturer uses its **own set of codes**, so an “F1” on one boiler may mean something completely different on another. Always check your boiler’s manual or the manufacturer’s website for model-specific information.
## Common Types of Boiler Fault Codes
While every brand is different, most fault codes fall into a few broad categories:
- **Low water pressure**
- **Ignition problems** (boiler not lighting)
- **Flame detection issues**
- **Overheating**
- **Sensor or PCB (circuit board) faults**
- **Fan or flue problems**
These issues range from simple fixes (like topping up pressure) to faults that must only be handled by a qualified engineer.
If in doubt, it’s always safer to [arrange a repair](https://www.trustedboiler.co.uk/boiler-repairs) rather than repeatedly resetting the boiler.
## Typical Fault Code Examples (By Problem Type)
Below are **generic examples** of what different fault types might look like. Exact codes vary by brand and model.
### 1. Low Boiler Pressure
Many boilers will lock out if the system pressure drops too low.
**Typical symptoms:**
- Fault code relating to “low pressure”
- Vaillant, Ideal - F75, F1, F22
- Worcester 1017W, LO-PR
- Baxi E119
- Pressure gauge below 1 bar
- Heating not working or cutting out
In some cases, you may be able to safely top up the pressure yourself using the filling loop, following the manufacturer’s instructions. If the pressure keeps dropping, there may be a leak or another underlying issue that needs professional attention.
> Ongoing pressure problems? Book a [boiler repair or inspection](https://www.trustedboiler.co.uk/boiler-repairs) with Trusted Boilers.
### 2. Ignition or Flame Failure
These codes indicate the boiler is struggling to light or keep the flame going.
Relevant fault codes include:
- Vaillant F28, Baxi E133, Worcester 227, Viessmann F4, Ideal L2
**Possible causes include:**
- Gas supply issues
- Faulty ignition components
- Blocked burner or flue
- Incorrect gas/air mixture
Because these issues involve the gas supply and combustion, they should only be investigated by a **Gas Safe registered engineer**.
### 3. Overheating and Safety Lockouts
Overheating codes are designed to protect your boiler and pipework.
Common causes can include:
- Pump failures
- Blocked or restricted pipework
- Limescale build-up in the heat exchanger
- Faulty thermostats or sensors
If your boiler is showing an overheating-related fault code, **do not** keep resetting it. Turn the boiler off and contact an engineer.
### 4. Sensor, Fan, or PCB Faults
Modern boilers rely on multiple sensors and an electronic control board (PCB). Fault codes in this area might point to:
- Faulty temperature or pressure sensors
- Fan speed or airflow issues
- Problems with the PCB or wiring
These are not DIY fixes and usually require proper testing, parts replacement, and safe recommissioning.
## Should You Try Resetting Your Boiler?
Most boilers have a reset function, and some minor, one-off faults can clear after a reset. However:
- **Never** reset a boiler repeatedly if the same fault code keeps returning
- **Never** attempt to open the boiler casing yourself
- If you smell gas, see scorch marks, or suspect a serious fault, turn the boiler off and contact the gas emergency number immediately
on 0800111999
If your boiler is regularly locking out with fault codes, it’s a sign that something needs attention. A professional repair is usually cheaper in the long run than ignoring the problem until the boiler fails completely.
## How Regular Servicing Helps Prevent Fault Codes
Many common issues that trigger fault codes can be reduced with **regular boiler servicing**. During an annual service, an engineer can:
- Check and clean key components
- Test safety devices and flue performance
- Spot early signs of wear or leaks
- Advise on any parts that may soon need replacing
Staying on top of maintenance helps keep your boiler efficient, reliable, and less likely to fail when you need it most.
You can learn more about our servicing options here:
[Boiler servicing and maintenance with Trusted Boilers](https://www.trustedboiler.co.uk/boiler-servicing).
## When to Call Trusted Boilers
You should contact a professional boiler engineer if:
- The same fault code keeps appearing
- You have no heating or hot water
- The boiler is making unusual noises
- You’re unsure what the code means or how serious it is
Trusted Boilers Ltd. provides **boiler repairs across South London and North Surrey**, including Sutton, Croydon, Wimbledon, Banstead, Epsom, and surrounding areas.
Book your repair or request advice here:
[Boiler repairs with Trusted Boilers](https://www.trustedboiler.co.uk/boiler-repairs).
## Thinking About Replacing an Unreliable Boiler?
If your boiler is regularly showing fault codes, breaking down, or is more than 10–15 years old, it may be more cost-effective to replace it with a modern, efficient combi boiler.
Find out more about our installation service:
[Combi boiler installation with Trusted Boilers](https://www.trustedboiler.co.uk/combi-boiler-installation).
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