Baxi E110 fault codewhat it means and how to fix it
The overheat thermostat has tripped. The boiler is producing heat that is not being carried away, and it should stay off until that is fixed.
Stop — this needs an engineer
Get a Gas Safe registered engineer to look at your Baxi E110
Gas Safe Register engineers only. No obligation.
What are the radiators doing?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
None of them heat up, but the boiler gets hot fast
Water is not leaving the boiler at all. This is the damaging condition.
Turn the boiler off at the front panel and leave it off until an engineer has seen it.
Hot at the top, cold at the bottom
Sludge restricting flow through the system and the exchanger.
The system needs cleaning, not just a component replaced.
Hot water has been getting weaker for months
Limescale. It degrades hot water performance first and eventually trips the overheat.
Ask about descaling and fitting a scale reducer, or it will recur.
What E110 means
E110 is a safety cut-out on overheat. The thermostat operates when the flow temperature exceeds its fixed limit, and the board latches the fault so the appliance cannot quietly restart. On a modulating condensing boiler, overheating is a flow problem rather than a heat problem: the burner output is controlled, so if the exchanger gets too hot it is because too little water is passing through it. Pump failure, sludge, closed valves and scale in hard water areas all produce the same picture. This is treated as a danger-severity fault because the component at risk is the heat exchanger, which on most boilers costs more than the appliance is worth.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Pump not circulating | Failed, seized, or set too slow for the system. | Common |
| Sludge restricting the heat exchanger | Magnetite narrows the waterways. Cold-bottomed radiators are the giveaway. | Common |
| Scale in the heat exchanger | Hard water areas. Weak hot water performance usually appears first. | Occasional |
| Failed overheat thermostat | The thermostat has failed closed and is reporting an overheat that is not happening. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£150–£1,200
Time on site
2 hours
Pump £280–£450. System clean £400–£700. Overheat thermostat £140–£220. Heat exchanger £600–£1,200.
Typical UK prices including parts and labour, updated August 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Central heating circulating pump
CH-PUMP-15-60£90–£180Plumbing merchant
Price checked 5 August 2026
Magnetic system filter, 22mm
MAG-22£65–£120Plumbing merchant
Price checked 5 August 2026
What other owners found
Nobody has shared what worked for them on this code yet. If you have had it, you would be the first — and it genuinely helps the next person.
Related Baxi fault codes
- E125Get it checkedThe boiler is not detecting enough water movement through it and has stopped. Usually the pump, an air lock, or a blocked filter.Related: overheat and circulation
- E9 219Stop — call an engineerThe boiler has overheated and the safety thermostat has tripped. Water is not carrying heat away from the exchanger, and it should not be run until that is fixed.Related: overheat and circulation
- L1Get it checkedThe boiler is not seeing enough water flow through it to run safely, so it has stopped. Usually a pump, an air lock, or a blocked filter.Related: overheat and circulation
- E02Get it checkedThe overheat thermostat has tripped. Almost always this means water is not moving through the appliance properly rather than that it is running too hot.Related: overheat and circulation
- F.20Stop — call an engineerThe overheat thermostat has tripped because the boiler got too hot. It has shut down to protect itself and it should not be restarted repeatedly.Related: overheat and circulation
- A02Get it checkedThe safety limit thermostat has tripped on overheat. In practice this nearly always means water has stopped circulating properly.Related: overheat and circulation
Related guides
Common questions about Baxi E110
Can I use it for hot water only?
No. If circulation is the problem, the same heat exchanger is at risk whichever circuit you use. Turn it off.
Why does it overheat with the thermostat set low?
The room thermostat decides how long the burner runs, not how hot the exchanger gets when water is not flowing through it. With no flow, the small volume inside reaches the cut-out in seconds regardless of the setting.
What is the worst case here?
A cracked heat exchanger, which is £600 to £1,200 to replace. On a boiler over twelve years old that usually means replacing the whole appliance, which is precisely why repeatedly resetting an overheat is such a false economy.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
- Interviews with working engineers
Checked by Technical reviewer (Gas Safe registration to be displayed on appointment) on 5 August 2026.