The Baxi E133 Fault Code Explained – A Clear, Professional Guide
Hello Heatlab readers, Lee here. Today we’re talking about one of the boiler fault codes we see most often in the field — the Baxi E133 fault. This error isn’t just for Baxi boilers — it also appears on Potterton and Main models because they use very similar ignition and gas control systems.
What the E133 Fault Code Actually Means
If your boiler displays E133, it’s telling you it has tried to ignite but has failed to detect a flame and gone into a safety lockout. This is a safety behaviour — the boiler is designed to stop working rather than run unsafely.
The core issue can relate to either the gas supply or the ignition/flame detection system, and the boiler will refuse to fire until the underlying cause is resolved.
Common Causes of E133
Here are the main reasons E133 occurs — listed in the order we see them on real jobs:
Gas Supply Problems
If the boiler isn’t getting enough gas — whether because the gas is turned off, your meter has run out of credit, or there’s a drop in gas pressure — the boiler won’t light.
Frozen or Blocked Condensate Pipe
This is a very common seasonal cause. When temperatures drop below freezing, especially in the colder months, the condensate pipe running to the outside of the house can freeze or block. Baxi’s own guidance confirms that E133 (and other fault codes) can be caused by a frozen condensate pipe.
Ignition or Flame Detection Components
If ignition electrodes, flame sensors, or related wiring are damaged or degraded, the boiler may spark but not register the flame.
Faulty Gas Valve or Internal Control Components
A gas valve that doesn’t open properly, PCB issues, or similar internal faults will prevent normal ignition.
How to Recognise an E133 Fault
If your boiler shows E133, you’ll usually see:
-
The E133 code on the display
-
Boiler attempts to start but cuts out
-
No flame detected
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No heating or hot water until the fault is resolved
Safe Preliminary Checks (What
You
Can Do)
There are a few simple, non-invasive checks that are safe for homeowners to perform:
Confirm Your Gas Supply
Check that your gas supply is on. Try your hob or other gas appliances. If you have a prepayment meter, make sure it has credit.
Check for a Frozen Condensate Pipe
Look for frost or ice on the condensate pipe if it runs outside — this is a very common cause in cold weather. Thawing the pipe with warm water can get you running again temporarily.
Try One Boiler Reset Only
Sometimes a reset clears a temporary lockout. Press the reset button according to your boiler manual and wait a few minutes to see if the fault clears.
These steps won’t fix internal component failures, but they cover the most common easy checks.
What Should
Not
Be Attempted by a Homeowner
It’s important to stress what you shouldn’t try:
-
Opening the boiler casing
-
Cleaning ignition electrodes internally
-
Touching gas valves or internal circuits
-
Testing gas pressure or flame sensing
These require training, certification, and calibrated tools — they’re not DIY jobs.
When to Book a Gas Safe Engineer
If the E133 fault comes back after a reset, or if the simple checks above don’t solve it, it’s time to call a Gas Safe registered engineer.
A professional will be able to:
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Check gas pressure accurately
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Inspect and test ignition and flame detection components
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Diagnose internal controls and wiring
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Confirm whether a condensate issue or an internal fault is the cause
Trying to fix these yourself isn’t just unsafe — it can make the situation worse.
Why You Shouldn’t Ignore E133
E133 isn’t just an annoyance — it’s a safety-related lockout. Boilers display this code because they cannot safely ignite gas. Continuing to try and operate the boiler, or repeatedly resetting it, can mask deeper issues or lead to more costly failures.
Tips to Reduce E133 Faults
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Insulate or reroute external condensate pipes to reduce freezing risk
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Book an annual service
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Address small issues early before they develop into ignition lockouts
Regular preventative care significantly reduces the likelihood of faults like E133.
Summary
E133 is a safety lockout caused by ignition or gas supply problems.
The most common causes are frozen condensate pipes, supply issues, ignition/flame detection faults, and internal component failures. You can conduct a few safe checks, but beyond that a Gas Safe registered engineer should diagnose and repair the fault. Prompt action helps ensure safety, reliability, and long boiler life.