Glossary · Faults, servicing and gas safety
What does the E133 fault code mean on a Baxi boiler?
E133 is a fault code on Baxi boilers that Baxi's own error code list describes as a gas supply fault. The boiler has shut down. Baxi says a frozen condensate pipe can cause it, and gives warming steps. Anything else is for a Gas Safe registered engineer.
Key points
- Baxi's error code list describes E133 as a gas supply fault, and names the power supply, sensing electrode, spark electrode and cable as things to check.
- Baxi says a frozen condensate pipe can make the boiler shut down with E133 and a few other codes.
- Baxi's thawing steps use a hot water bottle, a microwaveable heat pack or warm water from a watering can. It says not to use boiling water.
- The electrodes and cable are inside the boiler, so that part is for a Gas Safe registered engineer.
- Codes differ between brands and between Baxi models. Check your own manual.
What causes an E133 fault
Baxi’s error code list, in the technical support section of its website, describes E133 as a gas supply fault. It says to check the power supply, sensing electrode, spark electrode and cable.[1]Baxi, Error codes The page is written for installers, and Baxi points installers to its Baxi Works portal for fixes.[1]Baxi, Error codes The same list gives related codes. E128 is a safety error for frequent loss of flame, E134 is a gas valve that has been open without gas and E125 is a water circulation fault.[1]Baxi, Error codes
A separate Baxi help page for homeowners adds a cause you can check. It says that if your boiler has shut down and shows E133, or one of several other listed codes, your condensate pipe may be frozen.[2]Baxi, What do Baxi error codes E23, E53, E133, E119 and E128 mean? The condensate pipe carries waste water from the boiler to a drain. If part of it runs outside, it can freeze in very cold weather.
The page title lists a code as E23 but the text lists E28. This looks like a typing error on Baxi’s page, so check your manual for the code your boiler shows. E133 appears in both the title and the text.[2]Baxi, What do Baxi error codes E23, E53, E133, E119 and E128 mean?
So the code can have two very different causes. One is a frozen pipe, which you can deal with. The other is a fault inside the boiler, which you cannot.
What you can check yourself
If the weather is freezing and the code is E133, Baxi gives these steps for a frozen condensate pipe.[2]Baxi, What do Baxi error codes E23, E53, E133, E119 and E128 mean?
- Switch the boiler off at the control panel and turn off the electricity at the wall.
- Find where the pipe is frozen, usually the most exposed part.
- Warm the pipe along its exposed length using a hot water bottle, a microwaveable heat pack or warm water from a watering can. Do not use boiling water straight from the kettle, as this could damage the pipe.
- Turn the power back on at the wall and restart the boiler.
- Repeat the process until the boiler works again.
Take care on icy ground. If you cannot reach the pipe safely, or you are unsure which pipe it is, do not force it. Ask an engineer.
When to call an engineer
The parts Baxi names for E133 are inside the boiler: the electrodes and the cable. A householder should not open the casing or touch gas parts. Work on a gas appliance, including its gas valve, ignition and flue, must be done by a Gas Safe registered engineer.[3]Health and Safety Executive, Domestic gas: frequently asked questions A boiler repair visit can test the ignition system and gas supply to the boiler.
If thawing the pipe does not clear E133, or it returns, stop and book an engineer. Repeated lockouts are a sign of a cause that needs finding. If you smell gas at any time, leave the property and call the National Gas Emergency Service on 0800 111 999.[3]Health and Safety Executive, Domestic gas: frequently asked questions
Example
Sophie in Heckmondwike finds her Baxi combi shut down on a freezing morning with E133 on the display. She checks the hob, which works, so the gas is on. She switches the boiler off, finds the outside condensate pipe frosted along its length, and holds a warm hot water bottle against it. After a few minutes of repeating that, the ice clears. She switches the power back on and restarts the boiler. It lights.
If it had not, she would have booked an engineer for the boiler.
What people get wrong
It is natural to read “gas supply fault” as “I have no gas” or “there is a gas leak”. Neither has to be true. Baxi’s own help page ties E133 to a frozen condensate pipe in cold weather, and the list also points to electrodes and a cable inside the boiler. Check the easy things, then stop.
The other mistake is repeating a reset over and over. A reset does not remove a cause that is inside the boiler.
The bottom line
E133 on a Baxi boiler is listed by Baxi as a gas supply fault, and Baxi says a frozen condensate pipe can be behind it. In freezing weather, warm the pipe using Baxi’s steps and never use boiling water. If that does not clear it, or the code returns, the electrodes, cable and gas parts need a Gas Safe registered engineer.
Common questions
What does E133 mean on a Baxi boiler?
Baxi's error code list calls it a gas supply fault. Baxi's help page also says a frozen condensate pipe can cause E133 and the boiler to shut down, so it does not always point to the gas supply.
Can I fix E133 myself?
Only if the cause is a frozen condensate pipe, where Baxi describes warming the pipe. Anything inside the boiler, such as the electrodes, cable or gas valve, must be dealt with by a Gas Safe registered engineer.
How do I thaw a frozen condensate pipe on a Baxi?
Baxi says to switch the boiler off at the panel and the wall, find the frozen part of the pipe, warm it with a hot water bottle, heat pack or warm water from a watering can, then restart. Do not use boiling water.
Does E133 mean there is a gas leak?
Not necessarily. Baxi lists it as a gas supply fault, but also says a frozen condensate pipe can cause it. If you smell gas, leave the property and call the National Gas Emergency Service on 0800 111 999.
Sources
We cite the original source for every figure: government, regulators, standards bodies and manufacturers' own documents. Each one shows the date we last checked it.
- Baxi. Error codes. Checked 11 November 2026. ↩
- Baxi. What do Baxi error codes E23, E53, E133, E119 and E128 mean?. Checked 11 November 2026. ↩
- Health and Safety Executive. Domestic gas: frequently asked questions. Checked 11 November 2026. ↩