E110 is an overheat lockout on Baxi, Potterton, Main and Biasi — the safety thermostat has tripped because primary water got too hot, almost always because it was not circulating: a sludged filter, an airlock, a failing pump or a stuck diverter valve. Navien is the odd one out, using E110 for a combustion air-pressure fault. Overheats deserve respect: let it cool, reset once, and if it returns, stop resetting and get an engineer before the heat exchanger suffers.
The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.
| Brand | What E110 means | Severity | DIY? |
|---|---|---|---|
B Baxi | The E110 code means your Baxi boiler's safety thermostat has detected that the primary water temperature has climbed beyond its safe upper limit — typically somewhere in the 90–100°C range… Full guide → | Lockout — engineer likely | No |
B Biasi | The E110 code appears on Biasi boilers — including the Inovia and Advance Plus ranges — when the built-in safety thermostat detects that the boiler's internal temperature has climbed to an… Full guide → | Lockout — engineer likely | No |
M Main | The E110 code on a Main (Eco Compact) boiler means the overheat safety thermostat has activated and shut the boiler down. Full guide → | Lockout — engineer likely | No |
| NNavien | The E110 code means the Navien unit's control board has detected that air pressure within the combustion system is outside the acceptable operating range. Full guide → | Lockout — engineer likely | Some checks |
P Potterton | The E110 code appears on your Potterton boiler when the internal safety thermostat has tripped because the boiler reached an unsafe temperature. Full guide → | Stop & check now | No |
The E110 code means your Baxi boiler's safety thermostat has detected that the primary water temperature has climbed beyond its safe upper limit — typically somewhere in the 90–100°C range — and has shut the boiler down as a protective measure. The boiler will not fire again until the underlying cause is identified and resolved. This is a hard lockout, meaning a simple reset alone is unlikely to provide a lasting fix unless the root cause is addressed first.
The E110 code appears on Biasi boilers — including the Inovia and Advance Plus ranges — when the built-in safety thermostat detects that the boiler's internal temperature has climbed to an unsafe level and has shut the appliance down as a precaution. On older Biasi models such as the Riva Plus and Garda, this same condition may be shown as A02 rather than E110. In either case, the boiler will not restart until the root cause of the overheating is identified and resolved. You may notice a complete loss of heating and hot water, and in some cases banging or gurgling sounds that indicate poor water circulation within the system.
The E110 code on a Main (Eco Compact) boiler means the overheat safety thermostat has activated and shut the boiler down. The boiler's internal temperature climbed beyond a safe threshold — either in the primary heat exchanger or the surrounding pipework — and the safety cut-out tripped as a protective measure. This is a deliberate safety response rather than a component failure in itself; the underlying cause still needs to be identified and resolved before the boiler will run reliably again. Main boilers share the Baxi Heating group fault-code system, so this code carries exactly the same meaning across Main, Baxi, and Potterton branded appliances.
The E110 code means the Navien unit's control board has detected that air pressure within the combustion system is outside the acceptable operating range. A pressure switch continuously monitors the differential between ambient air and the combustion chamber — when it senses a restriction or anomaly in airflow, it triggers E110 and locks the unit out as a precaution. While the lockout is active, the gas valve is closed and the burner is not firing, so there is no active combustion and no risk of carbon monoxide production from the unit in this state.
The E110 code appears on your Potterton boiler when the internal safety thermostat has tripped because the boiler reached an unsafe temperature. Rather than continuing to run and risk damage or danger, the boiler shuts itself down as a protective measure. You will lose both heating and hot water, and you may hear banging or gurgling from the system. Potterton shares its fault code system with Baxi and Main boilers — all three brands are under the same parent company and use identical codes, so E110 means exactly the same thing and is diagnosed in exactly the same way across all three ranges.
Causes, fixes & costs for Potterton E110 → · All Potterton codes
No. E110 means different things on different brands — see the table above. Always identify your boiler's brand (it is printed on the front casing) before acting on any advice about the code.
On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. The underlying repair usually needs a registered engineer. Never open the boiler casing yourself.
For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.
General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.
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