Potterton E133 fault code explained

Potterton E133 means the boiler has locked out because the gas supply was interrupted, ignition failed or the flame was not detected. On some older displays the code alternates between E1 and 33. It is a safety lockout and a useful starting point, but it does not identify a failed part by itself.

If you smell gas, suspect a leak or have a carbon-monoxide warning, do not reset the boiler. Follow the emergency advice below. With no safety warning, you can record the exact model and code, check for an obvious property-wide supply problem and follow the reset instructions for that model once. If E133 remains or returns, arrange a Gas Safe registered engineer.

What does Potterton error E133 mean?

Baxi’s current technical error-code page includes the Potterton Assure Combi and System ranges and lists E133 as a gas-supply fault. Potterton service literature for models using the older E-code format gives the fuller explanation: the gas supply may have been interrupted, ignition may have failed, or the flame may not have been detected.

For the boiler to operate, gas must be available, ignition must occur and the control system must prove a stable flame. If that sequence is not completed, the boiler stops for safety. The display reports the result of the failed sequence; it cannot tell a homeowner whether the cause is at the meter, elsewhere in the supply, in the ignition system or in another internal component.

Potterton produced several ranges with different controls and fault systems. E133 information for an Assure, Promax, Gold or Apollo model should not automatically be applied to every Potterton boiler. Photograph the data badge only if it is visible without opening the casing, and use the manual for the exact model.

Why does the display alternate between E1 and 33?

Some Potterton displays cannot show all three digits at once. The manufacturer’s Apollo service instructions explain that E133 may appear as E1 alternating with 33. That still represents one code, not two separate faults.

Wait long enough to see the complete sequence and take a short video or two photographs. Also record any warning lights or other symbols. This prevents an engineer being told only “E1”, which may be incomplete information.

What should you do first?

1. Treat a gas smell as an emergency

If you smell gas or think an appliance is unsafe, do not try to clear E133. HSE advises calling the National Gas Emergency Service on 0800 111 999, opening doors and windows, and shutting off the gas at the meter control valve if you know how to do so safely. Do not operate electrical switches, smoke or use a naked flame in the affected area.

If a carbon-monoxide alarm sounds, or anyone has symptoms such as headache, dizziness, nausea, breathlessness, unusual tiredness or confusion, move into fresh air and seek urgent medical advice. Leave the boiler off until the property and appliance have been made safe.

2. Record the exact boiler and circumstances

Note the full model, the complete display sequence and when the lockout occurred. Was the boiler trying to heat radiators, produce hot water or restart after a power or gas interruption? Has it happened once or repeatedly? These details help distinguish a one-off external interruption from a persistent appliance fault.

Do not remove the boiler front to find a serial number or inspect components. The combustion case and internal gas, ignition and flue parts are not homeowner-access areas.

3. Check for a wider gas-supply issue

Only when there is no gas smell or other safety concern, consider whether the whole property has lost gas. If you have a prepayment meter, confirm it has credit and is not displaying a supply message. If another familiar gas appliance is normally available, note whether it is also affected, but do not repeatedly try to light appliances.

If all gas appliances appear to have stopped, contact the supplier or gas network as appropriate. Do not force a valve, dismantle a meter or attempt to purge gas pipework. A boiler repair cannot restore a network, meter or account-related interruption.

4. Check power and external controls

Confirm that the boiler display is powered and, where relevant, the programmer and room thermostat are requesting heat. This will not repair E133, but it gives the engineer a clearer description of the conditions in which the lockout occurs.

Do not bypass controls, replace internal fuses or test live wiring. Baxi’s technical E133 table includes the power supply among professional checks, which is not an instruction for DIY electrical work inside the boiler.

5. Use the correct reset procedure once

Reset controls differ between Potterton ranges. The Apollo service instructions describe turning the selector to Reset for at least five seconds for E133, while Assure models may use a dedicated reset button. Use only the procedure in the user guide for your exact boiler.

Baxi’s reset guidance says that frequent lockout indicates a fault and the installer or service engineer should be contacted. One correct reset may be reasonable after an external interruption has definitely cleared. Repeatedly restarting the appliance is not a repair and can erase useful fault history.

Is Potterton E133 a low-pressure fault?

No, not on the Potterton E-code tables used for this guide. Older Potterton service literature uses E119 for primary water pressure below 0.5 bar, while E133 concerns gas supply, ignition or flame detection. Do not open the filling loop or add water solely because E133 is displayed.

If the pressure gauge also appears low, record the cold reading and check the exact manual. Two conditions can exist at once, but topping up the heating circuit will not fix a failure to establish or detect a flame.

Can a frozen condensate pipe trigger E133?

Baxi-group homeowner guidance says E133 can sometimes be associated with a frozen condensate pipe on relevant boilers. That possibility is most credible during freezing weather when the appliance has an external condensate route. It is not proven by the code alone.

Inspect only pipework visible and reachable safely from ground level. Do not climb, separate joints, insert objects or use a flame. Baxi’s guidance recommends gentle heat such as a hot-water bottle, heat pack, warm cloth or warm water and specifically warns against boiling water, which can damage plastic and create a slip risk when it refreezes.

If you cannot identify the condensate pipe, it is inaccessible or damaged, or the fault remains after a model-approved homeowner step, stop and call an engineer. Internal condensate checks require the boiler to be opened.

What might an engineer investigate?

The engineer should confirm the exact Potterton model and fault history before testing. Depending on the manufacturer’s service instructions and evidence on site, checks may cover the incoming gas supply and operating pressure, electrical supply, ignition spark, flame-sensing or ionisation signal, gas valve operation, combustion, fan and flue route, wiring and condensate drainage.

Baxi’s current table mentions the power supply, sensing electrode, spark electrode and cable for E133 on the group that includes Potterton Assure. These are diagnostic areas, not a shopping list. A fault in any one is not established until it has been tested, and an external interruption must not be overlooked.

Professional checks can involve gas-carrying parts, the combustion case, live electricity and combustion-analysis equipment. Do not clean or bend electrodes, adjust the gas valve, disturb the flue or order a control board based only on E133.

Does E133 mean the gas valve is broken?

No. A gas-valve problem is one possible engineer finding, but E133 does not prove it. Several Potterton tables use separate codes for specific gas-valve connection or command faults. The lockout can also follow an interruption outside the boiler or a failure to create or detect a flame.

Parts swapping without measurements can be expensive and may leave the real cause unresolved. A competent engineer should test the supply and appliance before recommending a component.

Why does E133 return after a successful reset?

A reset only asks the boiler to try its start sequence again. If the underlying problem is intermittent—such as unstable supply pressure, a deteriorating ignition or sensing component, a connection fault, condensate restriction or a combustion issue—the boiler may run briefly and lock out later.

Record how long it operates, whether the fault occurs on heating or hot-water demand, and whether weather conditions appear relevant. Do not keep resetting it to maintain service. A recurring safety lockout needs diagnosis.

When should you arrange a repair?

Call a Gas Safe registered engineer if the code does not clear after one correct reset, if it returns, if there are other codes, or if you cannot identify the correct manual. Unusual noises, soot, staining, damage near the flue or any concern about safe operation are also reasons to stop using the boiler.

HSE says anyone employed to work on domestic gas appliances must be Gas Safe registered and competent for that area of work. Check the engineer’s ID card and the categories listed on the reverse.

What should you tell the engineer?

• the exact Potterton range and model;
• whether the display shows E133 continuously or alternates E1 and 33;
• whether heating, hot water or both were requested;
• whether other gas appliances appear to have supply;
• whether a prepayment meter has credit or a warning;
• whether the fault followed a gas or power interruption;
• whether one correct reset changed the display;
• the outside temperature and any visible condensate icing;
• how often the lockout has occurred; and
• any smell, alarm, staining or unusual noise.

Frequently asked questions

Can I keep resetting a Potterton E133 fault?

No. Use the model-specific reset once after any known external interruption has cleared. A code that stays or returns needs investigation.

Is E1 then 33 a different fault from E133?

Not on the older Potterton display described in the Apollo literature. It alternates the digits because it cannot show all of E133 at once.

Will topping up the pressure fix it?

Not normally. E119 is the low-pressure code in the relevant Potterton table. Only add water when the exact manual and gauge show that the heating circuit needs it.

Can I replace the ignition electrode myself?

No. Ignition and flame-sensing work requires the boiler to be opened and safety-critical tests to be completed by a competent Gas Safe engineer.

Does E133 mean the boiler must be replaced?

No. It is a lockout, not a replacement verdict. The decision depends on the diagnosed cause, the boiler’s age and condition, parts availability and the cost of a safe repair.

Related boiler-help guides

• Boiler not firing up: safe checks
• Why does my boiler reset keep failing?
• How to deal with a frozen condensate pipe
• Baxi E133 fault code explained