Baxi boilers are one of the most popular brands in the UK — but when an error code flashes up on the display, it can be worrying. The good news is that most Baxi error codes point to a specific fault that can be fixed with the right spare part.
In this guide, we explain every common Baxi boiler error code, what it means, and which boiler spare part you need to fix it. All parts listed are available from Boiler Spares Ltd with fast UK delivery.
E119 — Low Water Pressure
What it means: Your boiler pressure has dropped below 0.5 bar.
Common causes:
- Leak in the system
- Faulty pressure sensor
- Recently bled radiators
How to fix it: Re-pressurise the boiler via the filling loop. If the pressure keeps dropping, you may need a new pressure sensor or expansion vessel.
E133 — Ignition Lockout
What it means: The boiler tried to ignite but failed.
Common causes:
- Faulty ignition electrode
- Blocked burner
- Gas supply issue
How to fix it: Check the gas supply first. If that’s fine, the ignition electrode is the most likely culprit. We stock compatible ignition electrodes for all major Baxi models.
E168 — Flame Detection Fault
What it means: The boiler lit but lost the flame.
Common causes:
- Dirty or worn flame sensor
- Electrode gap incorrect
- Condensate blockage
How to fix it: Clean the flame sensor. If the fault persists, replace the ignition/detection electrode kit.
E125 — Circulation Fault (Pump)
What it means: Water isn’t circulating properly.
Common causes:
- Failed circulation pump
- Airlock in the system
- Blocked heat exchanger
How to fix it: Bleed the radiators. If the pump is hot but silent, it has likely seized. Replace the circulation pump — we stock Grundfos and compatible alternatives.
E110 — Overheating
What it means: The boiler has exceeded its safe temperature limit.
Common causes:
- Faulty thermostat
- Pump failure
- Sludge in the system
How to fix it: Check the pump is running. If the pump is fine, replace the thermostat or NTC thermistor.
E78 — Diverter Valve Fault
What it means: The diverter valve is stuck or failing.
Common causes:
- Worn diaphragm inside the valve
- Seized valve motor
- Scale buildup
How to fix it: In many cases, you don’t need a full valve — a diverter valve repair kit with a new diaphragm and seals will fix it. Much cheaper than calling an engineer.
E117 — Water Pressure Too High
What it means: Pressure is above 2.5–3 bar.
Common causes:
- Overfilled system
- Faulty pressure relief valve
- Expansion vessel has lost its charge
How to fix it: Release pressure via a radiator bleed valve. If it keeps happening, replace the safety valve or expansion vessel.
E1 — No Flow / Airlock
What it means: The boiler can’t detect water flow.
Common causes:
- Airlock after maintenance
- Faulty flow switch
- Low system pressure
How to fix it: Re-pressurise and bleed the system. If the error remains, the flow switch may need replacing.
E28 — Flue Fault
What it means: The boiler detects a problem with the flue.
Common causes:
- Blocked flue
- Damaged flue seal
- Condensate backing up
How to fix it: Check the flue for obstructions. Replace any damaged flue seals or gaskets.
E40 / E41 / E42 — Central Heating Sensor Faults
What it means: The boiler can’t read the central heating temperature.
Common causes:
- Faulty NTC thermistor
- Wiring issue
- Loose connection
How to fix it: Replace the thermistor. These are inexpensive and easy to fit.
Quick Reference Table
Table
| Error Code | Fault | Likely Part Needed |
| E119 | Low pressure | Pressure sensor, Expansion vessel |
| E133 | Ignition lockout | Ignition electrode |
| E168 | Flame lost | Ignition/detection electrode |
| E125 | Circulation fault | Circulation pump |
| E110 | Overheating | Thermostat, Thermistor, Pump |
| E78 | Diverter valve | Diverter valve repair kit |
| E117 | High pressure | Safety valve, Expansion vessel |
| E1 | No flow | Flow switch |
| E28 | Flue fault | Flue seal |
| E40–E42 | Sensor fault | Thermistor |
When to Call a Gas Safe Engineer
While many Baxi faults can be fixed with the right spare part, any work involving gas components, the gas valve, or the boiler casing must be carried out by a Gas Safe registered engineer. Always isolate the boiler and follow safe working practices.
Shop Baxi Boiler Spares
At Boiler Spares Ltd, we stock thousands of genuine and compatible Baxi boiler parts — from ignition electrodes and pumps to diverter valve repair kits and thermistors. Based in Huddersfield, we offer fast UK delivery so you can get your heating back on quickly.