Error E133

Safety first

- If you smell gas, get everyone out, do not use any electrical switches, do not light matches or use naked flames. Call the emergency gas number immediately (in the UK 0800 111 999) and your gas supplier. Do not attempt repairs.

- If you are not confident with any of the steps below, stop and call a Gas Safe registered engineer. Never work on the gas train, gas valve, or internal combustion components unless you are qualified.

Initial checks a homeowner can safely do

1) Check other gas appliances: turn on a gas hob or another gas appliance. If they do not light, you have a gas supply issue — contact your gas supplier.

2) Prepay meter/credit: if you have a pay-as-you-go meter ensure you have credit available.

3) Gas cock at meter: visually check the gas isolation tap at the meter is fully open (handle in line with the pipe). If you are unsure, call the supplier or a Gas Safe engineer.

4) Reset the boiler correctly: create a demand (turn on a hot water tap so the boiler registers demand), then press and hold the boiler reset/on button for the time described in your manual (typically 1–3 seconds). The boiler will attempt to relight (it may try up to 5 times before locking out again). If the fault clears and the flame symbol appears, monitor operation.

5) Check the flue/terminal: look outside to the flue terminal for obvious obstructions (debris, snow, bird nest). If clear, reset the boiler again. Do not crawl into confined spaces or remove flue components yourself.

Specific diagnostic steps you can attempt if comfortable (basic, low-risk tasks)

6) Frozen condensate pipe (common in cold weather): locate the plastic condensate pipe (usually runs from the bottom of the boiler to an outside drain). If it has frozen you can carefully thaw it by pouring warm (not boiling) water over the frozen section or wrapping a warm cloth around it. Have a bucket to catch water if you need to disconnect the low-level trap under the boiler. After thawing, reset the boiler. Insulate the condensate pipe afterwards or fit a short insulated sleeve or trace heater if freezing is frequent.

7) Condensate drain check under the boiler: if you are confident and the manufacturer manual allows, you can place a bucket under the condensate connection and carefully disconnect the external condensate pipe to check it drains. If water flows, that indicates the internal condensate route can be cleared. Reconnect it securely afterwards. If you see lots of water in the combustion area or inside the heat exchanger, stop and call an engineer.

Checks and repairs that require a Gas Safe registered engineer (do not attempt yourself)

- Testing and adjusting gas working pressure and checking the gas regulator or gas valve for correct operation.

- Purging air from the gas line or re-establishing the gas supply after any work on the supply pipe.

- Inspecting, cleaning, adjusting or replacing ignition electrodes, ignition leads, or the PCB and carrying out insulation/resistance checks.

- Internal inspection and draining of water from the heat exchanger if condensate has backed up into combustion parts, or diagnosing smoke recirculation issues.

- Replacing the gas valve, regulator, or other sealed components.

When to call a professional

- The E133 returns after you have done the safe checks and reset procedures.

- You cannot restore the gas supply to other appliances, or you saw signs of a supplier cut-off or meter issue.

- You smell gas or suspect a leak.

- You find water in the combustion chamber or internal areas, or you are not sure how to safely remove/inspect condensate water or the electrode leads.

What to tell the engineer

- Exact error code (E133), what you tried (reset, thawed condensate, checked gas to other appliances), whether other gas appliances work, and whether you saw any water draining when you checked the condensate. Also tell them if the fault is intermittent or constant.

If the basic homeowner checks above do not clear the fault, do not continue attempting internal fixes. Call a Gas Safe registered engineer or contact Baxi support for guidance. They will have the tools to measure gas pressure, test the ignition sequence, purge the gas line safely, and replace any faulty parts.