Main boiler fault codes — what they mean and what to do

Seeing an E-code on your Main Eco Compact or Eco Elite? Here's what it's telling you, what's safe to check yourself, and when to call a Gas Safe registered engineer.

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Find your code fast

Main boiler fault codes appear as E-numbers such as E119, E133 and E110 on Eco Compact and Eco Elite models. E119 is low water pressure and is usually a quick top-up; E133 is a gas or ignition fault, often a frozen condensate pipe in winter; E110 is an overheat lockout that needs an engineer. Use the table below to find your code.

Main is part of the Baxi group, so Eco Compact, Eco Elite and Main Combi boilers use the same E-code system you'll see on Baxi and Potterton. The code numbers and their meanings are shared across all three ranges — only the boiler models and the layout of your filling loop differ.

The wording can vary slightly by model year, so check your Main user guide for the exact text on your display. We'll always tell you which codes are a safe homeowner check and which need a Gas Safe registered engineer — and we'll never ask you to touch anything to do with gas.

Key facts

Codes show as E-numbers on Main Eco Compact and Eco Elite models.
E119 = low water pressure below 0.5 bar — usually a DIY top-up.
E133 = gas or ignition fault, often a frozen condensate pipe in winter.
E110 = overheat lockout — a Gas Safe registered engineer is needed.
Main shares the Baxi group E-code system, so the diagnostic steps match Baxi and Potterton.
Smart Plan boiler & central heating cover is a service plan, not insurance: parts and labour up to £500 a year, or up to £200 a year if the boiler is over 7 years old.
On the older-boiler tier, one engineer-only repair — a fan, pump or PCB — can use up much or all of that £200 yearly limit, so weigh it up before you switch.
Call-outs run Mon–Fri 08:00–18:00. A £95 call-out fee applies in the cases set out in your plan terms, and a 12-month agreement period starts once you use a service.

Main boiler fault codes at a glance

Code	What it means	Likely cause	DIY or engineer
E119	Low system water pressure — pressure has dropped below 0.5 bar.	A leak, recently bled radiators, or a tired expansion vessel.	DIY — top up via the filling loop. Engineer if it keeps dropping.
E133	Gas supply interrupted, flame not detected or ignition failed.	Frozen condensate pipe (the main winter cause), gas supply issue, or ignition fault.	Partly DIY — thaw the condensate pipe and check your gas supply. Otherwise engineer.
E110	Overheat — the safety thermostat has tripped and shut the boiler down.	A jammed pump or air in the circuit.	Engineer. Don't keep resetting an overheat fault.
E125	Water circulation fault in the primary circuit.	Pump fault, sludge or a blockage, or low pressure.	Engineer. You can check pressure first.
E160	Fan or fan-wiring fault.	Failed fan motor or a wiring/connector fault.	Engineer.
E20	Central heating NTC sensor fault (short or open circuit).	Faulty flow sensor or its wiring.	Engineer.
E28	Flue NTC sensor fault — sometimes linked to frozen condensate.	Sensor fault, or a blocked/frozen flue and condensate in freezing weather.	Partly DIY in winter (thaw condensate). Sensor work is engineer only.
E128	Flame failure during operation — the flame was detected then lost.	Gas supply dip, frozen condensate, or an ignition/flame fault.	Engineer. Don't keep resetting.
E130	Flue overheat protection has operated.	Flue overheat, often circulation or flue related.	Engineer.

Main E119: low water pressure (the most common code)

E119 is the code most Main owners see. It means the primary water pressure has fallen below 0.5 bar, so the boiler stops rather than run dry. It's usually a simple fix and one of the few you can safely sort yourself.

On an Eco Compact or Eco Elite, the filling loop is the silver braided hose beneath the boiler with a valve at each end. Topping up brings the pressure back into the normal range.

How to repressurise a Main boiler

Follow these steps once, with the boiler switched off and cool:

Find the filling loop — the braided silver hose under the boiler with a valve at each end.
Open both valves slowly and watch the pressure gauge.
Close the valves once the gauge reads roughly 1.0–1.5 bar.
Turn the boiler back on and reset it once if the code is still showing.
If the pressure keeps dropping after a top-up, you likely have a leak or a failed expansion vessel — book a Gas Safe registered engineer.

Main E133: gas or ignition fault (and frozen condensate)

E133 means the gas supply was interrupted, the flame wasn't detected, or ignition failed. In cold weather the most common cause by far is a frozen condensate pipe — the white plastic pipe that runs from your boiler to an outside drain. When it freezes, the boiler can't get rid of its condensate and locks out on E133.

There are a couple of safe checks before you call anyone. Make sure your other gas appliances work — if the hob won't light either, it may be a wider gas supply issue. If you're on a prepayment meter, check you're in credit.

Thawing a frozen condensate pipe

If you can safely reach the frozen section of external pipe, pour warm — never boiling — water over it, or hold a warm cloth or hot-water bottle against it until it thaws. Then reset the boiler once.

If E133 comes straight back, stop there. Anything involving the gas valve, ignition electrode or flame circuit is a Gas Safe registered engineer's job, not a DIY one. If you ever smell gas, call the National Gas Emergency Service on 0800 111 999 straight away, open windows, turn off the gas at the meter, don't touch electrical switches, and leave the property.

Main E110 and other codes (E125, E160, E20, E28, E128, E130)

E110 is an overheat lockout. The boiler's primary water got too hot and the safety thermostat tripped, usually because the pump is jammed or there's air in the circuit. It's the boiler doing its job. Don't keep resetting it — repeated resets can mask a genuine safety fault. Book a Gas Safe registered engineer.

The remaining codes point to internal parts and all need an engineer:

E125 — water circulation fault

The primary circuit isn't circulating properly — often a pump fault, sludge or a blockage. You can check the pressure is correct, but the diagnosis and fix are an engineer's job.

E160 — fan fault

The fan isn't running at the right speed, or its wiring has failed. This needs testing and a part fitted by an engineer.

E20 and E28 — sensor faults

E20 is a central heating NTC sensor fault; E28 is a flue NTC sensor fault. In freezing weather E28 can also be linked to a frozen condensate pipe, so it's worth checking that in winter — but replacing a sensor is engineer only.

E128 and E130 — flame and flue faults

E128 means the flame was detected then lost during operation; E130 is flue overheat protection. Both are engineer-required — don't sit and reset them.

Which Main faults can I fix myself?

Only a short list of Main faults are safe homeowner jobs. Everything that touches the gas valve, flame, fan, pump, flow or PCB is a Gas Safe registered engineer's work.

The safe checks are: topping the pressure back up for E119, thawing a frozen external condensate pipe for E133 or E28, checking your gas supply and prepayment credit, and resetting the boiler once. If a code returns after a single reset, stop and book an engineer rather than resetting again.

Safe to try yourself:

Repressurise via the filling loop when you see E119.
Thaw a frozen external condensate pipe with warm (not boiling) water for E133 or a winter E28.
Check your other gas appliances work and, on a prepayment meter, that you're in credit.
Reset the boiler once — never repeatedly, and not for an overheat code like E110.

When to call a Gas Safe registered engineer

If you've done the safe checks and the code won't clear — or it's an overheat, fan, sensor or flame code from the start — the next step is a Gas Safe registered engineer. Call us on 0333 772 6247 or build your plan online.

Main boilers are common in rented and social housing, so if you're a landlord this is worth sorting quickly — a working boiler is part of your gas safety duties, and our landlord cover is built around that. Pinning down your Main code early also helps you weigh up a one-off repair against ongoing cover instead of guessing.

Smart Plan is a service plan, not insurance. Our boiler & central heating module sends an engineer from a national network of vetted, Gas Safe registered engineers, with parts and labour included up to your cover limit — up to £500 a year if your boiler is under 7 years old, or up to £200 a year if it's older. That older-boiler limit is worth weighing up: on the many older Main boilers common in rented and social housing, a single engineer-only repair like a fan, pump or PCB can use up much or all of the £200, so the plan may only fund part of a big job — you'd pay the balance. Call-outs run Mon–Fri 08:00–18:00. A £95 call-out fee applies in the cases set out in your plan terms, so read those before you buy to see when it would apply to you. Cover is modular, so you pick only what you want. Once you use a service, a 12-month agreement period begins — it's a commitment to plan for, not a one-off. We've looked after over 15,000 customers, and we're from UK Boiler Company Ltd, trading since 2014.

Main boiler fault code FAQs

What does E119 mean on a Main boiler?

E119 means the water pressure in your Main boiler has dropped below 0.5 bar. Repressurise to around 1.0–1.5 bar using the filling loop. If the pressure keeps falling, you likely have a leak or a failed expansion vessel and should book a Gas Safe registered engineer.

What does E133 mean on a Main boiler?

E133 signals an interrupted gas supply, an undetected flame or ignition failure — and in cold weather it often means a frozen condensate pipe. Check your gas supply and thaw the external pipe with warm (not boiling) water, then reset once. If it persists, book a Gas Safe registered engineer.

Are Main and Baxi fault codes the same?

Yes. Main is part of the Baxi group, so Eco Compact and Eco Elite boilers use the same E-code system. E119, E133 and the other E-codes mean the same on Main, Baxi and Potterton, and the diagnostic steps are the same across all three ranges.

How do I clear a fault code on a Main boiler?

For pressure or condensate codes, fix the underlying cause first — top up the pressure or thaw the condensate pipe — then reset the boiler once. For gas, flame, fan or overheat codes, don't keep resetting; book a Gas Safe registered engineer, as repeated resets can mask a more serious fault.

Does Smart Plan cover an older Main boiler, and what does it cost me?

Yes, but read the limit. Boiler & central heating cover is a service plan, not insurance. Parts and labour are included up to your cover limit — up to £500 a year, or up to £200 a year if the boiler is over 7 years old. On the older-boiler tier one bigger engineer-only repair can use up much of that £200, so you may pay the balance on a large job. A £95 call-out fee applies in the cases set out in your plan terms, call-outs run Mon–Fri 08:00–18:00, and a 12-month agreement period starts once you use a service.

What should I do if I smell gas?

Call the National Gas Emergency Service on 0800 111 999 straight away. Open your windows, turn off the gas at the meter, don't touch any electrical switches, and leave the property.

Main code still showing? Book a Gas Safe registered engineer.

Build an ongoing Smart Plan boiler & central heating module, or call us to book a repair. It's a service plan, not insurance: parts and labour are covered up to your cover limit — up to £500 a year, or up to £200 a year if your boiler is over 7 years old, which one bigger repair can use up. Call-outs run Mon–Fri 08:00–18:00, a £95 call-out fee applies in the cases set out in your plan terms, and a 12-month agreement period starts once you use a service.