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Main Fault Codes
Main Fault Codes: What They Mean And What To Do
Reviewed by our Gas Safe registered engineers · Last updated 21 July 2026
Main is a value-focused brand within the same manufacturing group as Baxi and Potterton, and it’s a common find in smaller flats and rental properties across North London where a straightforward, budget-friendly boiler was chosen. Fault codes typically appear as a letter F followed by a digit.
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Quick answer: F1 usually relates to ignition and F4 to the fan — both are safety lockouts. F28 often relates to pressure or flow issues and can sometimes be resolved by repressurising via the filling loop.
Common Codes
Common Main fault codes
Below are the codes we’re called out for most often on Main boilers. If yours shows something different, note it precisely and call us.
| Code | Meaning | First step |
|---|---|---|
| F1 | Ignition fault | One reset can be tried; don’t repeat if it recurs |
| F4 | Fan fault | Needs an engineer — not something to reset repeatedly |
| F28 | Pressure or flow fault | Check and top up pressure via the filling loop |
| Code | Meaning | First step |
|---|---|---|
| E10 | Outdoor sensor fault | Needs an engineer — sensor or wiring |
| E20 | Central heating (flow) sensor fault | Needs an engineer — sensor or wiring |
| E28 | Flue sensor fault | Needs an engineer — sensor or wiring |
| E50 | Hot water sensor fault | Needs an engineer — sensor or wiring |
| E53 | Flue blockage detected | Don’t keep resetting; needs an engineer |
| E78 | Water pressure sensor fault | Check the gauge; if normal, needs an engineer |
| E109 | Poor circulation before ignition | Often pump or air related — call an engineer |
| E110 | Overheat lockout | Don’t keep resetting; book an engineer |
| E117 | System pressure too high | Bleed a little off; if it stays high, needs an engineer |
| E119 | Low water pressure | Repressurise via the filling loop to around 1–1.5 bar |
| E125 | Poor primary circulation (pump) | Check pressure; if normal, needs an engineer |
| E128 | Flame loss during operation | One reset can be tried; if it recurs, needs an engineer |
| E133 | Ignition failure or gas supply fault | Check the gas is on and the condensate isn’t frozen; if it recurs, call an engineer |
| E160 | Fan fault | Needs an engineer — fan or wiring |
| E168 | Circuit board / general fault | Needs an engineer |
Engineer Advice
What we see most often with Main boilers
- Main boilers are built to a lower price point than Baxi’s premium range, reflected in slightly shorter typical warranty terms — so it’s worth checking servicing requirements to keep cover valid.
- In our experience, Main boilers are common in landlord-managed flats, where consistent annual servicing sometimes slips between tenancy changeovers. Worth flagging to whoever manages the property.
- Parts for Main boilers are generally straightforward to source given the shared platform with Baxi and Potterton, keeping repair turnaround reasonably quick.
What Repairs Typically Cost
Typical Main repair costs
Figures are general guidance for North London; Main’s shared parts with Baxi and Potterton usually keep costs and turnaround reasonable. We quote before any work begins.
FAQs
Main fault codes — your questions answered
Is Main a reliable boiler brand, or is it too budget-focused to trust?
Main boilers are generally reliable for their price point, being built by the same group as Baxi with a straightforward, no-frills design. They’re a sensible choice for smaller properties without excessive demands on the system.
If I’m a tenant, who’s responsible for a Main boiler fault code?
In a rented property, boiler faults and servicing are the landlord’s legal responsibility, so a tenant seeing a fault code should report it to their landlord or letting agent rather than arranging a repair themselves.
Does F28 always mean the same as low pressure codes on other brands?
It typically relates to pressure or flow, similar in spirit to the low-pressure codes seen on Baxi and Potterton given the shared platform, though always check by looking at the actual pressure gauge reading.
Are Main boiler parts harder to find than premium brands?
No, generally the opposite — given the shared components with Baxi and Potterton, parts availability is usually good and repair turnaround reasonably quick.
How long do Main boilers typically last compared to premium brands?
With proper servicing, a similar lifespan to most mainstream boilers, typically 12–15 years, though the exact figure depends more on water hardness and maintenance history than the specific brand tier.
Why would my landlord’s Main boiler show F1 repeatedly in a rental property?
Recurring ignition faults in rental properties are sometimes linked to inconsistent servicing between tenancies — worth flagging to the landlord that a full diagnosis, not just repeated resets, is needed.
Is it worth upgrading from a Main boiler to a Baxi when it’s time to replace?
It can be a sensible step up if you want a longer standard warranty and slightly more advanced features, since Baxi generally sits above Main in the same group’s range. That said, if your Main boiler has served you reliably and your needs are modest, a like-for-like Main replacement is equally valid depending on budget and priorities.
As a landlord with several Main boilers, is there a way to keep servicing simpler to manage?
Yes — we regularly work with landlords managing multiple properties and can set up a consistent servicing schedule across a portfolio, often at a reduced per-property rate when several are booked together. Keeping dates aligned, or at least tracked centrally, makes it much easier to stay on top of certificates and avoid the gaps that happen between tenancy changeovers.
Related
More help and our repair service
Main’s premium sister brand — shared platform, overlapping codes.
Read guide Fault CodesPotterton Fault CodesAnother brand in Main’s group with closely related fault codes.
Read guide PressureBoiler Losing PressureBehind a recurring F28: why pressure keeps dropping and how to fix it.
Read guide Boiler ProblemsBoiler Not Igniting / LockoutWhat sits behind an F1 ignition fault, and what’s safe to try.
Read guide LandlordGas Safety Certificate (CP12)For landlords with Main boilers across rental properties.
Read guide MaintenanceAnnual Boiler Service GuideKeep a Main boiler’s cover valid with annual servicing.
Read guideBrowse the full Boiler Fault Code Library for other brands, or head back to the Help & Advice Centre. We repair Main boilers across North London — see our boiler repair service, and keep cover valid with annual boiler servicing.
Got a Main fault code we haven’t listed?
Call us with the exact code and we’ll tell you honestly what it means — and what it will cost to put right. Same-day appointments subject to availability.
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