Baxi boiler E133 error: what it means and what to do

Error E133 on a Baxi boiler indicates an ignition lockout or failure to detect a flame. Possible causes include an interruption to the gas supply, an ignition system fault or, on certain condensing models, problems with condensate drainage. Provided there is no smell of gas or any other warning sign, you can check for a supply interruption and carry out the reset permitted by the manual. If the warning returns, the boiler needs a professional diagnosis, not further attempts to start it.

If you have a problem with your boiler, you can use our free error code finder. It can help you identify errors and find straightforward, effective guidance on resolving them.

The lockout protects the ignition process but does not identify a faulty part

The boiler must start combustion and confirm that a flame is present before it can continue allowing gas through. When that sequence does not complete correctly, the control system stops operation and displays the warning. This means E133 describes the outcome of a fault, not necessarily its origin: a supply interruption and a flame detection problem can produce the same message.

Some displays show E133; others show 133 or alternate between E1 and 33. That difference in presentation does not establish what has gone wrong. The exact model and its manual matter because fault codes depend on the range and should not automatically be applied across all Baxi, Baxi Roca or other manufacturers’ boilers.

The usual result is a loss of heating and hot water produced by the burner. You may also hear the fan running and attempts at ignition before the lockout appears. Those sounds provide context, but they do not prove that gas is reaching the burner or allow you to distinguish externally between a worn electrode, a valve fault or a control problem.

A photograph of the display, the model and the point at which the fault occurs are more useful than repeatedly clearing the warning. Noting whether it happens when a hot tap opens, when heating is requested or after a few seconds of operation helps preserve information for the diagnosis. There is no need to trigger additional faults to collect it: simply describe what has already happened.

A smell of gas changes what you should do

An E133 warning alone does not confirm a leak. However, if you smell gas, restoring hot water is no longer the priority: do not press RESET or try to light another appliance. Do not operate switches, plugs or electrical devices in the affected area, and avoid flames or any other source of ignition.

Leave the area and contact your gas network’s emergency service from a safe location. Ventilate only if you can do so immediately without putting yourself at risk, and do not stay inside searching for the source. If a carbon monoxide alarm sounds or anyone feels unwell in a way that could suggest exposure, leave the property and seek emergency assistance; carbon monoxide cannot be detected by smell.

You should not reset the boiler if there is soot, an unusual smell of combustion, water on electrical components or damage to the flue. In those circumstances, the appliance must remain out of use until it has been inspected. A cleared code does not establish safety when there are physical signs of a combustion, flue or sealing problem.

The gas supply problem may be outside the boiler

Before assuming a part has failed, check whether the gas network has reported an interruption and whether the problem started after work in the building or a known outage. For homes supplied from a storage tank, the availability of fuel also matters. These checks may reveal a cause outside the appliance without dismantling anything or working on the installation.

The position of an accessible gas isolation valve may provide information, provided you can identify it with certainty. Do not force a stiff valve, lubricate it or dismantle connections. If it was closed and you do not know why, do not simply open it: it may have been shut for maintenance, an incident or a safety issue that has not yet been resolved.

If another gas appliance was working normally before the lockout, that suggests a general supply was available, but it does not confirm that the boiler is receiving the required flow or pressure. You do not need to light a cooker to test this, particularly if there is any suspicion of a leak. Gas pressure requires professional measurement and cannot be determined from the heating pressure gauge.

Air may be present in the gas pipe after an interruption or work on the installation, but that does not make it safe to purge the pipe yourself. Never loosen a connection to release gas or use repeated ignition attempts instead of an inspection. Gas pipe purging must be carried out by an appropriately qualified professional using the correct equipment and safety checks.

The reset method depends on the controls and has a practical limit

A reset may restore operation once a temporary cause has been resolved, such as a gas supply interruption. Use only the control intended for the user and follow the instructions for the exact model. Some appliances require the reset button to be held for 2 seconds; on others, the duration, button or selector position differs.

Published instructions for different Baxi models refer to buttons held for 2 to 5 seconds, R or RESET buttons and rotary selectors. These procedures are not interchangeable. References to five resets or a 15-minute wait should not be treated as universal either: the applicable limit is the one in your manual, not the instructions for a boiler that looks similar.

If there are no warning signs, a manufacturer-approved reset can establish whether the lockout was temporary. If E133 returns immediately or reappears after ignition, do not keep trying. A reset does not repair the cause, and using up the available number of resets does not provide a more reliable diagnosis.

If the boiler starts working and then fails again, keep a note of that behaviour. A temporary recovery does not prove the problem is resolved or justify keeping it running through repeated resets. When the warning recurs, take the appliance out of use with its normal user control and arrange an inspection, even if it manages to produce hot water between lockouts.

Condensate drainage and the flue can also play a part

In a condensing boiler, some of the water produced during combustion leaves through a dedicated drain. A blockage in that route can affect operation and contribute to a lockout. An external section exposed to sub-zero temperatures can also freeze. This possibility relates to particular appliances and installations, rather than being an automatic explanation for every E133 warning.

From a safe position, you can look for visible ice, a distorted external pipe or unusual dripping. Do not climb a ladder to inspect it or disconnect the drain. Checking the trap and internal pipework is a job for a professional because the condensate system contributes to safe boiler operation and is not simply an independent household waste pipe.

If the manual allows an accessible external section to be thawed, follow its instructions and avoid boiling water, flames, tools or improvised electrical heating. If you cannot confidently identify the pipe, or water could reach electrical connections, stop at a visual inspection. Do not pour chemicals into the system in an attempt to clear a blockage either.

The boundary is even clearer with the flue: you can look from ground level for an obvious obstruction at the outside terminal, but must not dismantle it, insert objects or activate calibration functions. Suspected recirculation or faulty exhaust arrangements require professional inspection of combustion and the flue system, even if another guide suggests solving the problem with a combination of buttons.

Similar-looking codes do not always mean the same thing

Reading the exact number helps avoid confusing an ignition problem with a water pressure or flue issue. The following table covers related warnings found in certain Baxi ranges; it is not a universal code dictionary for the brand. The manual for the exact model remains the reference for confirming the meaning and the action permitted.

The distinction between E133 and E118 is particularly important. The former concerns the ignition sequence; the latter indicates a water pressure condition in the ranges shown. Although some installations use a reference range of 1.2 to 1.5 bar when cold, that reading does not measure gas pressure or provide a solution to an E133 lockout.

This also explains why generic advice can be counterproductive: E10 does not have a single meaning across every series, and E25 should not be confused with ignition failure. You can read and record the pressure without intervening, but do not fill or drain the circuit to try to clear E133. Any additional warning needs to be interpreted separately, with the model identified.

Ignition can fail even when fuel is available

When the supply is available, the diagnosis moves towards ignition and flame confirmation. A worn electrode, a faulty connection or a control problem can prevent the sequence from completing. Hearing sparking does not rule out these causes: producing a spark is not the same as confirming a stable flame under the conditions required by the appliance.

On certain models, detection problems associated with moisture or internal leaks have also been reported. A burner that lights and then stops shortly afterwards may help guide an inspection, but it does not identify a component on its own. If water appears beneath the boiler, do not remove the casing to locate the leak or attempt to dry connectors or reposition wires.

The electronic control board is another possibility, not a conclusion that can be drawn from the code. Before attributing the fault to it, a professional needs to check the conditions required for ignition and the signals reaching the controller. E133 does not justify buying a board, electrode or valve without a diagnosis: several different causes share the same warning.

Gas pressure measurements, internal electrical checks, electrode cleaning and combustion adjustments are outside the scope of user maintenance. Activating automatic calibration through technical menus is not a user task either. These operations require an appropriately qualified professional and checks afterwards, not merely getting the number to disappear from the display.

The cost depends on the cause, not the number on the display

There is no single repair price for E133. A supply interruption may not require any boiler components to be replaced; an internal fault involves different work. Giving a fixed amount without a diagnosis would be misleading. To assess the expense, it is more useful to know which check confirms the cause and what specific work the professional proposes.

Before accepting a visit, establish whether call-out and diagnostic charges are separate and whether they are deducted if the repair goes ahead. A monthly maintenance price is not the same as the cost of fixing this fault either: coverage and conditions may apply. The quotation should separate the charges and explain any exclusions that could affect the work.

If you have a warranty, insurance or maintenance agreement, check the required process before arranging work elsewhere. Opening the appliance or replacing parts yourself adds risks and may complicate a claim assessment. This does not mean every intervention automatically removes all your rights, but do not assume coverage without checking the terms.

Deciding between repair and replacement requires more than the appliance’s age. Its overall condition, repeated faults, spare part availability and the total repair cost compared with a newly installed boiler all matter. An isolated E133 does not prove the boiler is worn out; equally, a pattern of significant faults should not be ignored simply because each reset restores operation.

Restoring service means more than clearing the warning

A boiler that restarts after a known supply interruption and does not repeat the fault presents a different situation from one that needs regular resets. In the second case, the lockout points to an unresolved condition. Stable operation matters more than a single successful ignition, and a record of what happened helps distinguish between those situations.

At home, the safe scope is to identify the model, read the code, check for external supply incidents and use the normal controls as instructed by the manual. Beyond that, work involving gas, combustion, internal wiring or pressurised water belongs to a qualified professional. With a persistent E133, the next step is diagnosis, not repeated resets: this avoids spending money on the wrong parts and mistaking a temporary recovery for a repair.