Baxi E110 fault codewhat it means and how to fix it
The safety thermostat has tripped on overheat — "overheat of the primary water" in Baxi's words. One reset is allowed on every generation. If it trips again, the water is not moving.
Stop — this needs an engineer
Get a Gas Safe registered engineer to look at your Baxi E110
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What happens after one reset?
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.
It runs normally and does not come back
Probably a one-off air pocket or a brief circulation hiccup. Baxi's wording allows the single reset you have used.
Bleed any radiators that are cold at the top and mention it at the next service.
It trips again within a day
The water is not moving. Pump, air lock or a blocked heat exchanger — the things Baxi's flow checks in that order.
Stop resetting and book a Gas Safe registered engineer.
There is kettling or banging before it trips
Localised boiling in the heat exchanger, which is the obstruction case in Baxi's flow.
Engineer visit; expect a system clean and possibly a heat exchanger.
What E110 means
E110 is "Safety Thermostat Operated" in the selector-switch tables and "Safety thermostat operated" in the digital-display ones, and Baxi's explanation is the same across fifteen years of manuals: "E110 shows overheat of the primary water." A thermostat clamped to the heat exchanger has seen the water go past its limit and cut the burner. It is one of the few codes Baxi let the householder reset on every generation. The Platinum user guide: "If E110 or E130 is displayed overheat of the primary water or flue system has occurred. Turn the selector switch to the reset position and hold for at least 5 seconds. If the boiler does not relight, or the code is displayed regularly contact your installer or service engineer." The 600 and 800 manuals list 110 among the codes relit by "pressing the Reset button for 1 to 3 seconds".
Baxi's professional page splits the cause in two: "(i) Boiler max. temperature exceeded for gradient (probable pump jammed or air in the circuit). (ii) Safety thermostat sensor tripped." That first clause is the one to hold on to.
A heat exchanger only overheats if the burner is putting heat in faster than the water is taking it away, and the 600 Combi fault-finding flow for E110 asks one question — is the pump running? — and then says "if pump is running the heat exchanger could be obstructed". The EcoBlue Advance user guide goes further and prints two codes: "110 Safety Thermostat Operated (pump fault)" and "111 Safety Thermostat Operated (over temperature)". This page is rated danger because a boiler that trips its overheat stat repeatedly is one whose safety device is being used as a control, and because Baxi's own flow ends at a blocked heat exchanger, which is not something to keep resetting your way through.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Pump not running or not moving enough water | Baxi's first cause: "probable pump jammed". A seized pump, a pump head with a failed bearing, or a pump running on a system so sludged that its output goes nowhere. The 600 and 800 pump assembly is Baxi part 7684006. | Common |
| Air in the primary circuit | Baxi's second cause. An air pocket in the heat exchanger lets a section of it run dry and the thermostat sees the spike. The manual's remedy for the circulation codes is "ensure that the boiler and system are fully vented". | Common |
| Heat exchanger obstructed | The 600 Combi flow: "if pump is running the heat exchanger could be obstructed. Replace heat exchanger." Scale and sludge narrow the waterways until the pump cannot push enough through to carry the heat away. | Occasional |
| Safety thermostat or its wiring | Baxi's second clause, "safety thermostat sensor tripped", covers a stat that has drifted or a connection that has gone high-resistance. The 600 and 800 thermostat is part 7207653 and is the cheapest fix on this list. | Occasional |
| Diverter valve stuck | On a combi, a diverter that does not move fully leaves the pump pushing against a half-closed port. The 600 flow checks for 230 V at the diverter valve motor (part 7216534) in each mode. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£0–£600
Time on site
1h 30m
One reset costs nothing. Safety thermostat (Baxi 7207653) fitted £90–£150. Pump assembly (7684006) £200–£320 fitted. System flush £300–£500. Heat exchanger £450–£600 fitted.
Typical UK prices including parts and labour, updated September 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.
Magnetic system filter, 22mm
MAG-22£65–£120Plumbing merchant
Price checked 28 September 2026
Baxi / Potterton / Main safety (overheat) thermostat
7207653£15–£40Authorised Baxi parts distributor
Price checked 28 September 2026
Baxi / Potterton / Main pump assembly
7684006£120–£240Authorised Baxi parts distributor
Price checked 28 September 2026
Baxi / Potterton / Main diverter valve motor
7216534£45–£95Authorised Baxi parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Baxi fault codes
- E125Get it checkedBaxi's primary circulation fault, decided by two temperature tests the manuals spell out. Pump, air or a blocked filter; the pressure is usually fine.Related: overheat and circulation
- E.04.08Stop — call an engineer"Maximum safe temperature value reached": the safety thermostat has opened on a Baxi 200/400 Combi or Combi 2. Circulation first, the thermostat second, in Baxi's own order. One reset, then an engineer.Related: overheat and circulation
- E.01.17Get it checked"No water circulation (permanent)" on the Baxi 200/400 Combi and Combi 2, after H.01.18 has shown as a temporary block. Pressure, venting and the pump, in Baxi's order; reset once.Related: overheat and circulation
- E109Get it checkedPre-circulation fault on the digital-display Baxis: the board could not confirm water moving before it would light the burner. Vent the system; Baxi allow a reset from the button.Related: overheat and circulation
- E270Get it checkedBaxi's dry-fire circulation fault: the heat exchanger was heating with too little water passing through it. Air, a stopped pump or a closed circuit; not a code to reset repeatedly.Related: overheat and circulation
- E193Get it checkedPre-circulation fault on the selector-switch Baxis (Duo-tec Combi HE, Platinum, Megaflo HE A), shown as E1 then 93. Baxi offer no reset for it; the pump or air is the cause.Related: overheat and circulation
Own a Baxi boiler? Save it and its codes come first next time.
Related guides
Common questions about Baxi E110
How do I reset E110?
Selector-switch boilers (Duo-tec Combi HE, Platinum): turn the switch fully anticlockwise to R against the spring and hold for at least five seconds. Digital-display boilers (600, 800, Compact, Assure): press Reset for one to three seconds. Baxi say once; if it does not relight or comes back regularly, contact your engineer.
What is E111?
Only the EcoBlue Advance prints it. That boiler splits the overheat into "110 Safety Thermostat Operated (pump fault)" and "111 Safety Thermostat Operated (over temperature)". On every other Baxi both situations are E110.
Is E110 dangerous?
The boiler has protected itself, so at the moment it shows the code it is safe. The danger is in treating the safety thermostat as a reset button. It trips because the heat exchanger got too hot, and repeated trips stress the exchanger and mask a circulation fault that will get worse.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
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
- Manufacturer support portal
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.