Main E110 fault code: what the 110 error means
E110, which some Main boilers show as a flashing 110 with no letter in front of it, means the primary water inside your boiler overheated and the safety thermostat shut it down. Here is what causes it and when to call an engineer.
What does the Main Heating E110 fault code mean?
The Main E110 fault code means the safety thermostat has operated: the primary water inside the boiler got too hot, so the boiler locked itself out rather than carry on. Main is part of the Baxi group and shares its E-code system, and Baxi's published error-code list gives E110 as the boiler's maximum temperature being exceeded for the gradient, with a jammed pump or air in the circuit the probable reason, or the safety thermostat sensor tripping. Reset it once. If the code comes back, it needs a Gas Safe registered engineer.
A flashing 110 with a warning symbol and no E in front of it is the same fault. Some Main models print the code as E110 and others drop the letter and show 110 on its own, which is why people search for a Main boiler 110 error rather than E110. Either way the meaning and the response are the same.
The lockout is the safety system working, not the fault itself. One thing 110 does not mean: it is not a temperature. Baxi publishes no overheat figure against this code, so treat any page that tells you the boiler locks out at 110 degrees with caution.
Main does not publish a homeowner page for this code
If you searched Main's website and found nothing useful, that is not you missing it. The Main Heating website states that it has now transitioned into Baxi, and the error-code list now sits on baxi.co.uk. That list does include E110, but it is written for installers: it gives the fault and tells the reader to log in to Baxi Works for the actions, with no reset instructions and nothing on when a homeowner should call someone out. The homeowner explanations sit inside the PDF user guides, one per model range.
Key facts
The quick version, before the detail.
- Meaning: safety thermostat operated. The primary water overheated and the boiler locked out.
- Display: E110 on some Main models, a flashing 110 with a warning symbol on others.
- Published causes, from Baxi's error-code list: maximum temperature exceeded for the gradient, probably a jammed pump or air in the circuit, or the safety thermostat sensor tripped.
- Not a low-pressure fault. Baxi publishes low water pressure separately as E118, water pressure below 0.5 bar, and some Main and Baxi boilers show it as E119.
- Not a gas or flue fault either. Gas supply and ignition faults have their own code, 133, which a frozen condensate pipe often triggers, and a flue thermostat lockout shows as 130.
- DIY-fixable: no. Note the code, check the pressure gauge, reset once, then stop.
- Where it shows: the Eco Elite, Combi Eco and Eco Compact ranges all use the shared Baxi E-code system, so check the code list in your own user guide for your exact model.
- Gas emergency: if you smell gas or a carbon monoxide alarm sounds, call the National Gas Emergency Service on 0800 111 999.
- Smart Plan boiler and central heating cover is a service plan, not insurance: parts and labour up to £500 a year if the boiler is under 7 years old, or up to £200 a year if it is over 7. Cover is monthly and modular, but once you use a service a 12-month agreement period begins, and leaving early costs the remaining months or 75% of the outstanding balance.
Why does the Main E110 code appear?
Baxi publishes two causes against E110, and they apply to Main boilers because the two brands share the code system. The first is that the boiler's maximum temperature was exceeded for the gradient, with a jammed pump or air in the circuit named as the probable reason. The second is that the safety thermostat sensor has tripped. Both come back to one problem: hot water is not leaving the heat exchanger at the rate the boiler expects.
An engineer works through that in a set order. They look first at whether a system fault is causing the overheat. If not, the safety thermostat is tested for continuity across its terminals once the boiler has cooled, and replaced if the reading is out of tolerance. The flow and return sensors come next, and if 110 still flashes, replacing the control board is the last step.
Be wary of what other sites list. Low system pressure is not a published cause of E110: several pages have taken the description that belongs to the low-pressure code and attached it here, sending people off to top up a boiler that is in an overheat lockout. Frozen condensate pipes and blocked flues are not published causes either, and both have their own codes.
Main E110 causes and what happens next
| Likely cause | What you'll notice | Who deals with it |
|---|---|---|
| Pump jammed or failed, so heat is not circulated | Radiators stay cool while the boiler fires; the code returns soon after a reset. | Gas Safe registered engineer. The pump is internal work. |
| Air trapped in the primary circuit | Gurgling pipework, radiators cold at the top. | With the heating off and the radiators cool, bleeding a radiator is a normal householder job, but it will not on its own clear an overheat lockout. Purging air from the boiler's primary circuit is engineer work. |
| Safety thermostat sensor tripped or faulty | The code returns each time, though the system otherwise looks normal. | Engineer. Continuity is tested across the thermostat terminals once the boiler has cooled. |
| Flow or return sensor faulty | The boiler behaves as though it is hotter than it is, and the code recurs. | Engineer. Both sensors are checked as part of the diagnostic sequence. |
| Control board fault | 110 still flashes after the thermostat and sensors have been cleared. | Engineer. Replacing the board is the last step, after the thermostat and sensors. |
What can I safely check myself?
There is very little safe homeowner action on an overheat lockout, and none of it means opening the casing. Work through these four steps and no further.
1. Write the code down exactly as it appears, E110 or 110, so you can pass it to whoever attends.
2. Look at the central heating pressure gauge and note the reading. The needle normally sits in the green section, around 1.0 to 1.5 bar when the system is cold. If it reads low, top it up once using the filling loop as shown in your Main user guide. Topping up will not on its own clear an overheat lockout, because low pressure has its own code, but water that is barely there cannot circulate either.
3. Reset once, using the reset method printed in your own Main user guide, because the control layout and the hold time differ between ranges. Do not reset a second time.
4. Then stop. If the boiler does not relight, or the code keeps coming back, contact your installer or a Gas Safe registered engineer.
That is the limit. The pump, safety thermostat, sensors and control board sit behind the casing alongside live electrical parts, so testing any of them is qualified work.
Separately from the code, treat any gas smell or sounding carbon monoxide alarm as an emergency. Open the windows, turn the gas off at the meter if you safely can, avoid electrical switches, get everyone out and call the National Gas Emergency Service on 0800 111 999.
When to call a Gas Safe registered engineer
Call as soon as E110 or 110 returns after a single reset, or if it shows regularly even when the boiler restarts in between. A lockout that repeats means a part has failed or the water is not circulating.
Expect a methodical visit rather than a quick look. An engineer will confirm the electrical supply and check the gas pressure at the meter, run earth continuity and polarity tests, then work through the safety thermostat, the flow and return sensors and the control board.
You can book a one-off repair with us, or call us on 0333 772 6247. We aim to get an engineer out to you within two working days, which is an attendance target rather than a promise about the repair itself, alongside cover-plan call-out hours of Monday to Friday, 08:00 to 18:00. If you are booking a one-off repair rather than using a cover plan, appointments run Monday to Friday, 09:00 to 17:00, and one-off works carry no workmanship guarantee. Check anyone you use on the Gas Safe Register first.
If you would rather spread the cost of future breakdowns, a Smart Plan boiler and central heating module is the alternative to paying per visit. It is a service plan, not insurance, so it funds covered repairs up to a limit instead of paying a cash sum: up to £500 a year if your boiler is under 7 years old, or up to £200 a year if it is over 7, with anything above the limit paid by you. A £95 call-out fee, paid in advance, applies in your first 30 days, for faults the plan does not cover, no-access visits and early annual-service requests, and cover still applies in those first 30 days. Cover-plan call-outs run Monday to Friday, 08:00 to 18:00, with an engineer attending outside those hours only for a genuine emergency breakdown. Cover is monthly and modular, but using a module starts a 12-month agreement period the first time you use a service. There is a 14-day cooling-off period, and it ends the moment a service is carried out, after which leaving early costs the remaining months or 75% of the outstanding balance.
Main E110 and 110 fault code FAQs
What does E110 mean on a Main boiler?
The safety thermostat has operated because the primary water overheated, so the boiler locked out to stay safe. Main shares Baxi's E-code system, and Baxi's published list gives E110 as the boiler's maximum temperature being exceeded for the gradient, probably a jammed pump or air in the circuit, or the safety thermostat sensor tripping.
My Main boiler shows 110, not E110. Is it the same fault?
Yes. Some Main models show a flashing 110 with a warning symbol and no E, and others show E110. Both are the same overheat lockout and need the same response.
Is a Main 110 error caused by low pressure?
No. Baxi publishes low water pressure as a separate code, E118, water pressure below 0.5 bar, and some Main and Baxi boilers show it as E119. Some third-party sites wrongly attach that description to E110, but topping up will not on its own clear an overheat lockout.
How do I reset a Main boiler showing E110?
Use the reset method printed in your own Main user guide, because the control layout and the hold time differ between ranges. Reset once only. If the code returns, stop and book a Gas Safe registered engineer.
Why can't I find E110 explained on Main's website?
The Main Heating website has transitioned into Baxi, and the error-code list now sits on baxi.co.uk. That list describes E110 but points readers to Baxi Works for the installer actions, so the homeowner explanations sit only inside the PDF user guides.
Can I keep resetting the boiler if 110 comes back?
No. If the boiler does not relight, or the code shows regularly, contact your installer or a Gas Safe registered engineer. Repeated resets do nothing about the cause.
Which Main boilers show the E110 or 110 code?
Main is part of the Baxi group, so the Eco Elite, Combi Eco and Eco Compact ranges use the shared E-code system in which E110 is the overheat lockout. Check the code list in your own user guide to confirm what your exact model displays.
Seeing E110 or 110? Get a Gas Safe engineer booked.
Book a one-off repair and a Gas Safe registered engineer will look at it, or set up a Smart Plan boiler and central heating module. It is a service plan, not insurance: up to £500 a year under 7 years old, or up to £200 a year if older, with anything above that paid by you. A £95 call-out fee, paid in advance, applies in your first 30 days, for faults the plan does not cover, no-access visits and early annual-service requests, and cover still applies in those first 30 days. Using a module starts a 12-month agreement period the first time you use a service, and leaving early costs the remaining months or 75% of the outstanding balance. Call 0333 772 6247, Monday to Friday, 08:00 to 18:00.
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