Baxi E110: the overheat lockout that is really a circulation message
Baxi E110 locks the boiler out on overheat. The heat is real, and the reason sits on the water side more often than the burner side. Here is how to tell them apart.
What this means
Baxi uses E110 for an overheat condition, where the boiler has exceeded its permitted maximum temperature or the safety thermostat has tripped. The measurement is genuine, but heat only accumulates when something stops carrying it away, so the investigation belongs to the water side of the system more often than to the burner.
Equipment and model context
Baxi domestic gas boilers using the E-series fault codes listed in Baxi support material
- Baxi 800 combi
- Baxi 600 combi
- Baxi Duo-tec
- Baxi Platinum
Baxi publishes E-series codes across several domestic ranges, and the detail behind a number can differ between them. The list on the label behind the casing flap of your own appliance governs, and a Potterton or Main boiler from the same group carries its own published list even where components are shared.
What you may notice
- The boiler fires, temperature climbs quickly, and it locks out on E110 within a short period.
- Banging, knocking, or a kettle-like boiling sound comes from the boiler while it runs.
- Heating had been getting less effective across the house for some time before the lockout began.
Likely causes
- A pump that has seized, slowed, or been set too low leaves too little water passing through the heat exchanger to remove the heat being produced.
- Air trapped in the primary circuit takes the place of water and interrupts circulation without any component failing.
- Corrosion debris and sludge accumulated in the system restrict flow through the exchanger, radiators, or pipework.
Diagnostic paths
It boils audibly before it locks out
A sound like a kettle coming to the boil, or sharp banging, is audible from inside the casing during the short run before the code appears.
Stop using the heating entirely. That noise is water flashing to steam against hot metal, and each occurrence leaves deposits on the exchanger surface.
Some radiators have been cold for months
Parts of the house had been failing to heat properly well before the lockout, particularly radiators furthest from the boiler or on upper floors.
Map which radiators work and which do not, including whether cold ones are cold at the top or the bottom. That pattern tells an engineer where flow is being lost.
It started after the system was drained or refilled
The fault appeared shortly after a radiator change, a leak repair, or any work that involved emptying and refilling the heating circuit.
Report the work and its date. Air introduced during refilling is a circulation problem that arrives suddenly and has an obvious origin.
An overheat is an accounting problem. Gas delivers a known quantity of heat into the exchanger, water is the only thing carrying it out, and when the outgoing side falls the temperature inside has nowhere to go but up.
- Heat inSet by the burner firing rate
- Heat outCarried by circulating water
- ImbalanceExchanger temperature rises
- Safety tripThe appliance locks out
| Accompanying sign | Where to look | Urgency |
|---|---|---|
| Kettling or banging | Circulation and the heat exchanger | Stop using the heating now |
| Whole house lukewarm | Pump output or system-wide restriction | Arrange service promptly |
| One zone cold | Zone valve or that circuit | Arrange service |
| Follows recent refill | Air in the primary circuit | Arrange service, mention the work |
The difference between the symptom and the fault
Overheat codes are among the most misread in domestic heating, because the word points at the burner while the cause sits somewhere else. A boiler cannot overheat while water is moving through it at the designed rate; the water would simply carry the heat into the house. Reaching a temperature limit means the removal side failed, and the removal side is a pump, a circuit, and the radiators at the end of it.
Understanding that saves money as well as time. An engineer sent to look at a boiler that keeps overheating, who checks only the appliance, may replace a sensor or a thermostat and leave the sludge or the failing pump behind. The lockout then returns in a fortnight.
Why kettling changes the urgency
Noise from a boiler during an overheat event is not incidental. Kettling is water boiling in contact with the hottest surfaces of the exchanger, and each episode deposits scale that further reduces heat transfer at exactly the point where transfer is already failing. That makes the condition progressive rather than static, which is why the honest advice is to stop using the heating rather than to persist until an appointment is available.
It also gives an engineer something to act on. Kettling reported alongside an overheat lockout points toward flow and deposit problems rather than toward a control fault. The boiler pressure too high page covers the related symptom this fault often travels with, and the radiators cold at the bottom guide explains what different cold patterns mean.
What to give the technician
Provide the Baxi model and serial number, the E110 code, the cold pressure reading, the radiator map of what heats and what does not, any boiling noise, and details of recent system work.
Safe homeowner checks
- Check the system pressure gauge on the boiler and write down the reading while the system is cold.
- Feel every radiator after a heating attempt and record which warm up, which stay cold, and where on the panel the cold begins.
- Note any noise from the boiler and whether it coincides with firing, and stop using the heating if kettling is present.
Is a reset appropriate?
Baxi permits a reset from the control panel, and one attempt establishes whether the lockout repeats. Repeating it against unchanged circulation subjects the exchanger to the same overheating each time.
When to call a technician
- Pump testing and replacement, venting a sealed primary circuit, cleaning or flushing a system, and resetting a tripped safety thermostat are Gas Safe registered tasks.
- A boiler that boils audibly should not be run while waiting for an appointment, because each episode damages the heat exchanger surface further.
Questions people ask about this
Is Baxi E110 a boiler fault or a system fault?
The measurement is taken at the boiler, but heat only accumulates when circulation fails. Pumps, air, sludge, and closed valves live in the heating system rather than in the appliance, and they produce this code routinely.
How many times can I reset an E110?
One reset tells you whether the fault repeats. Beyond that, each attempt heats the exchanger under the same conditions that caused the trip, which risks scaling and damage rather than diagnosing anything.
Does low pressure cause E110?
Pressure and circulation are related but not the same. A system that has lost water often has air where water should be, and that air interrupts circulation, which is the mechanism behind the overheat.
Evidence recordHow this page was checked
official manufacturer support article · checked 2026-09-15
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Baxi technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- official manufacturer support article
- Scope of the definition
- Baxi domestic gas boilers using the E-series fault codes listed in Baxi support material
- Last checked
- 2026-09-15