Error code
Baxi Boiler Fault Code 133
The boiler has locked out after failing to light The most likely cause is gas supply interruption, meter issue, or closed emergency control valve. Check first: check user controls such as the timer, thermostat, and boiler display.
Quick answer
133: what does it mean and how to fix
What does it mean?
The boiler has locked out after failing to light
How to fix first
Check whether other gas appliances appear to have supply, without dismantling the boiler.
Why is this happening?
Gas supply interruption, meter issue, or closed emergency control valve
When should I call an engineer?
Call a Gas Safe registered engineer if 133 returns after one reset, other gas appliances work, you smell gas, or the boiler repeatedly tries and fails to light.
What does this error code mean?
Baxi boiler fault code 133 usually means the boiler tried to ignite but could not establish a safe flame, so it locked out. It is commonly associated with gas supply, ignition, or flame detection issues rather than a user-serviceable setting.
This code relates to the ignition and flame proving path, including gas supply, ignition electrode, flame sensing, condensate condition, fan, flue, gas valve, and controls.
Start with this safe check: Check whether other gas appliances appear to have supply, without dismantling the boiler. If the code returns, the fault worsens, or the appliance does not behave normally, call a Gas Safe registered engineer if 133 returns after one reset, other gas appliances work, you smell gas, or the boiler repeatedly tries and fails to light.
Symptoms users may notice
- The boiler may lock out before delivering heating or hot water.
- You may hear ignition attempts without the burner staying lit.
- The fault may appear after a gas supply interruption or in freezing weather on some systems.
What users often notice
- Baxi 133 often appears as a lockout code after the boiler has tried and failed to start.
Why is this happening?
- Gas supply interruption, meter issue, or closed emergency control valve
- Ignition electrode or flame sensing fault
- Condensate pipe issue on suitable condensing models in freezing weather
- Gas valve, fan, flue, or control fault requiring professional diagnosis
What this usually points to
This code relates to the ignition and flame proving path, including gas supply, ignition electrode, flame sensing, condensate condition, fan, flue, gas valve, and controls.
How to fix this safely
- Check whether other gas appliances appear to have supply, without dismantling the boiler.
- Check user controls such as the timer, thermostat, and boiler display.
- If the Baxi manual permits it, try one standard reset.
- If freezing weather is relevant, follow only the manual's safe external condensate guidance.
What not to do
- Do not keep pressing reset repeatedly.
- Do not remove the casing or touch ignition, gas, or combustion components.
Common misdiagnoses
- It can be assumed to be only a gas meter issue, but repeated 133 with normal gas supply points back to the boiler.
Reset steps
- Follow the reset instructions shown on the boiler control panel or in the manual.
- Allow one ignition attempt after the reset.
- If 133 reappears, stop resetting and book a Gas Safe registered engineer.
Intermittent vs persistent faults
A one-off 133 after a supply interruption may clear with one permitted reset; repeated lockouts should be treated as persistent.
When to call an engineer
Call a Gas Safe registered engineer if 133 returns after one reset, other gas appliances work, you smell gas, or the boiler repeatedly tries and fails to light.
Safety warning
Do not remove the boiler casing or try to work on gas, ignition, or combustion components yourself.
Useful hub links
Related ignition fault codes
Baxi Boiler Fault Code 125
Water circulation or pump performance issue
Baxi Boiler Fault Code 128
Flame detection has been lost during operation
Baxi Boiler Fault Code 130
Fan, flue, or air pressure sensing problem
Baxi Boiler Fault Code E110
the boiler has overheated or reached a high-temperature safety limit.
Relevant guide
Frequently asked questions
Can I keep resetting a Baxi boiler with 133?+
No. Try one permitted user reset only. If 133 returns, the ignition fault needs proper diagnosis.
Does Baxi 133 mean there is no gas?+
It can be caused by a gas supply issue, but it can also be an ignition, flame sensing, condensate, or control fault.
What if I smell gas with a 133 fault?+
Do not reset the boiler. Turn off the gas at the emergency control if safe, ventilate, avoid switches or flames, and call the National Gas Emergency Service.
Can I clean the ignition electrode myself?+
No. The electrode is inside the boiler casing and should only be checked by a Gas Safe registered engineer.