The boiler has sensed the primary water getting too hot and shut down on the overheat thermostat.
Most common on: Baxi 600, Baxi 800, EcoBlue, Platinum+, Duo-tec
E110 means the overheat (limit) thermostat has tripped: the primary flow temperature rose beyond a safe limit, so the boiler cut the burner to protect itself. It is a safety shutdown to prevent damage to the heat exchanger.
Overheating is almost always a circulation problem — if the heated water is not moving away from the heat exchanger quickly enough, its temperature spikes. That usually means a pump, airlock, low pressure or sludge issue rather than a burner fault.
Top up to about 1.0–1.5 bar (cold) if the gauge reads low, then reset the boiler.
Cold spots or radiators slow to heat can indicate sludge or a circulation problem worth flagging to an engineer.
Reset the boiler after topping up. If E110 returns quickly, do not keep resetting — there is a circulation fault to fix.
Persistent E110 needs a heating engineer to check the pump, sensors and heat exchanger, and possibly a system flush.
Work on the gas side of a boiler must be carried out by a Gas Safe registered engineer. The checks above are limited to safe, non-invasive things a homeowner can look at (pressure, resets, the gas supply) — if in doubt, stop and call an engineer.
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The boiler has sensed the primary water getting too hot and shut down on the overheat thermostat. E110 means the overheat (limit) thermostat has tripped: the primary flow temperature rose beyond a safe limit, so the boiler cut the burner to protect itself. It is a safety shutdown to prevent damage to the heat exchanger.
You can try a single reset and the safe checks below, but Baxi E110 usually needs a Gas Safe registered engineer. Never work on the gas side of a boiler yourself — it is illegal and dangerous unless you are Gas Safe registered.
A recurring E110 means the underlying cause has not been fixed — most often poor circulation from a failing or seized pump. Resetting repeatedly will not solve it; get the boiler diagnosed properly.
Circulation fault
Low water pressure
Flue gas thermostat / flue safety device
See all Baxi fault codes.