Main boiler error E133 means the appliance has locked out because the gas supply was interrupted, ignition failed or a flame was not detected. Main’s current error-code page shortens this to a gas-supply fault, while its Eco Compact service literature gives the wider explanation. The code identifies the stage at which safe operation stopped; it does not prove which component is faulty.
If you smell gas, suspect a leak or have a carbon-monoxide warning, do not reset the boiler. Follow the emergency advice below. If there is no safety concern, you can record the exact model and display, check for an obvious property-wide supply issue and use the reset instruction for your model once. A code that remains or returns needs professional diagnosis.
What does E133 mean on a Main boiler?
Main’s error-code table lists E133 for the Eco Compact Combi and System ranges as a gas-supply fault. The Main Eco Compact System installation and service manual expands on that: E133, E134 and E135 can be displayed when the gas supply has been interrupted, ignition has failed or the flame has not been detected. Its detailed table describes E133 as an interruption of gas supply or flame failure.
Those descriptions are consistent rather than contradictory. A boiler must receive gas, create an ignition spark and prove a stable flame before it can continue to run. If that sequence is not completed, the control system locks out the appliance. It cannot tell a homeowner whether the original cause is outside the property, in the meter, in the ignition system or elsewhere inside the boiler.
Codes vary between ranges. Check that your boiler is a Main model and record the full display, including the leading E and any other symbols. Use the user instructions for the exact model rather than a generic reset method found online.
What should you do first?
1. Stop if you smell gas
If you smell gas or believe an appliance may be unsafe, do not attempt a reset. HSE advises calling the National Gas Emergency Service on 0800 111 999, opening doors and windows, and turning 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 situation has been made safe.
2. Record the exact model and circumstances
Photograph the complete E133 display and note the model name. Write down whether the fault appeared while heating the house, producing hot water or immediately after a power or gas-supply interruption. Note whether it is a first occurrence or a repeat lockout.
Useful information is limited to what you can see without removing the boiler casing. Do not open the appliance to search for labels, electrodes, valves or wiring.
3. Check for an obvious wider supply problem
Only when there is no smell of gas or other safety concern, consider whether the whole property has lost its gas supply. If you use a prepayment meter, check that it has credit and is not showing a supply message. Main’s Eco Compact Heat user guide includes sufficient prepayment credit among its basic checks.
If you have another gas appliance that you normally use safely, you can consider whether it is also affected. Do not repeatedly attempt to light appliances, force a valve, dismantle a meter or purge gas pipework. If every gas appliance appears to have stopped, contact the supplier or gas network as appropriate. A boiler engineer cannot restore a network or account-related interruption.
4. Check power and heating controls
Main’s user guidance also asks owners to check that the boiler has power and the controls are switched on. Confirm that the programmer or thermostat is requesting heating where relevant. These observations do not repair E133, but they help describe whether the appliance is receiving a demand and showing a genuine lockout.
Do not remove fuses from inside the boiler, test live components or bypass a control. Internal electrical checks in Main’s service manual are written for competent engineers.
5. Follow the correct reset procedure once
The Eco Compact System service literature says that pressing the reset button for one to three seconds can relight the boiler when E133 is displayed. However, that instruction applies to the models covered by the manual. Controls on other Main boilers can differ, so follow the user guide supplied for your exact appliance.
A single manufacturer-approved reset may clear a one-off interruption after the underlying condition has gone. If it has no effect, or E133 appears regularly, Main says further investigation is required. Repeated resetting restarts the same sequence; it does not repair a gas-supply, ignition or flame-detection fault.
Is E133 caused by low boiler pressure?
Not according to the Main Eco Compact fault table. It assigns E118 to primary-system water pressure below 0.5 bar, while E133 concerns gas supply or flame failure. Do not open the filling loop or add water solely because E133 is shown.
If the pressure gauge is also outside the normal range, record that separately and use the exact manual. Overfilling the heating system will not help the boiler detect a flame and may create an additional fault.
Could a frozen condensate pipe be responsible?
A frozen or blocked condensate route can prevent some condensing boilers from operating during cold weather, but E133 by itself does not confirm that cause. Baxi-group homeowner information has sometimes associated E133 with condensate problems on relevant appliances, while the Main Eco Compact table describes the code through gas supply and flame failure. Model-specific instructions therefore matter.
If temperatures are below freezing and an external plastic condensate pipe is safely visible from ground level, record any obvious icing. Do not climb, disconnect joints, push objects into the pipe or use a flame. If your Main user guide provides a homeowner thawing method, follow it exactly and avoid boiling water. Otherwise arrange professional help.
What might an engineer investigate?
A competent engineer begins with the exact model, the fault history and whether a wider supply issue exists. Depending on the evidence and the manufacturer’s service instructions, investigation can include the gas supply and operating pressure, ignition and flame sensing, electrical connections, the gas valve, combustion, the fan and flue route, and condensate drainage.
Main’s public error-code page mentions the power supply, sensing electrode, spark electrode and cable among professional checks for E133 on the listed Eco Compact ranges. That is not a recommendation to replace those parts. Each item must be tested in context, and other causes must be ruled out.
These checks can involve gas-carrying components, the combustion circuit, live electrical testing and combustion-analysis equipment. Do not remove the casing, clean or bend electrodes, adjust the gas valve, disturb the flue or buy a part based only on the display.
Does E133 mean the gas valve has failed?
No. Main uses a separate E15 description for a gas-valve fault in the Eco Compact service table. That does not completely rule out the gas valve during an E133 investigation, but it shows why one code is not a parts diagnosis. An interruption before the boiler, failed ignition, missing flame signal or another safety condition can all prevent the sequence from completing.
Guessing at a gas valve or electrode can waste money and leave the actual problem unresolved. A qualified engineer should test before recommending a repair.
Why might E133 appear after the gas has been switched off?
If the meter, supply or an upstream valve has been interrupted, the boiler may try to light without a stable gas supply and then lock out. Once the supply has been restored by the responsible party and there is no smell of gas, follow the exact user guide for one reset.
Do not try to purge air from gas pipework or repeatedly cycle the boiler. Gas work is restricted to Gas Safe registered engineers who are competent for the task.
When should you call a Gas Safe engineer?
Arrange a repair if E133 does not clear after the limited checks and one correct reset, if it returns, or if the boiler shows other faults. Also call for help if you cannot identify the correct manual, the appliance behaves unusually, or you see soot, staining or damage around the boiler or flue.
Gas Safe Register is the official register of businesses and engineers legally permitted to carry out gas work in Great Britain. HSE advises checking the engineer’s ID card, which shows the categories of work they are qualified to undertake. Registration must cover the appliance and work involved.
What information will help the engineer?
- the exact Main range and model;
- a photograph of the complete E133 display;
- whether heating, hot water or both were requested;
- whether other gas appliances appear to have supply;
- whether a prepayment meter has credit;
- whether the fault followed a power or gas interruption;
- whether one correct reset changed the display;
- the outside temperature and any safely visible condensate icing;
- how often the fault has occurred; and
- any gas smell, alarm, staining or unusual noise.
This information can help an engineer prepare, but it cannot replace testing at the appliance.
Frequently asked questions
Can I keep pressing reset until my Main boiler fires?
No. Use only the correct reset method once after an obvious external interruption has cleared. If E133 stays or returns, further attempts are not a repair.
Is E133 always a problem with the gas coming into the house?
No. A property-wide interruption is one possibility, but Main also refers to ignition failure and failure to detect a flame. The code needs context and, when persistent, professional tests.
Can I clean the ignition electrode myself?
No. Reaching ignition and flame-sensing components means opening the boiler and entering safety-critical areas. That work belongs to a competent Gas Safe registered engineer.
Will repressurising fix Main E133?
Not normally. Main publishes E118 for low primary water pressure on the relevant Eco Compact table. Do not add water unless the gauge and exact user manual show that it is required.
Does E133 mean I need a new boiler?
No. It is a lockout code, not a replacement verdict. The sensible decision depends on the diagnosed cause, boiler age and condition, parts availability, warranty and repair cost.
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
Is your Main boiler still showing E133?
Book a fixed-price Incredaboil boiler repair and have the ignition lockout diagnosed safely by a qualified engineer.