- Boilers
- Gas boiler
E109
Baxi E109 on a gas boiler: air in the boiler circuit
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
Baxi E109 means air is present in the boiler circuit, a temporary fault. Read the gauge with the system cold: Baxi asks for 1 to 1.5 bar. If E109 stays, Baxi says to call the authorised technical service.
Safety first
Stop and check this first
- If you smell gas: Baxi says to switch the boiler off, not to operate any electrical device or switch on lights, to put out any flame and open the windows. Then leave the home and call your gas distributor's emergency number and the service centre from outside.
- Baxi says to contact the authorised technical service if the pressure drops often: topping up again and again brings fresh air into the circuit.
Safe checks you can perform
- System pressure when cold
- Slow filling with the boiler tap
- If E109 stays
- Inspection by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Pump check
- Do not attempt this professional task: Pump power wiring
- Do not attempt this professional task: Bleeding the circuit and test
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Pump check
What they doThe technician checks that the boiler pump starts and moves the water round the circuit.
They must show youthe pump running and the pressure at item 05.
In writingthe pump condition and, if replaced, its part number.
Pump power wiring
What they doThe technician checks with a multimeter that the pump receives voltage and that the wiring is properly connected.
They must show youthe voltage measured at the pump.
In writingthe fault found and the repair.
Bleeding the circuit and test
What they doThe technician bleeds the air from the primary circuit and radiators and tests the boiler on heating.
They must show youa full demand with no 109.
In writingthe final cold pressure.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
System pressure when cold
- Who:
- you.
- How:
- with the system cold, read the gauge under the boiler or hold the info key for at least 1 second and look at item 05, system pressure.
- Result that matters:
- whether the pressure is between 1 and 1.5 bar, as Baxi asks.
- If it is low:
- move on to filling.
- If it is correct:
- lack of water is ruled out; carry on.
- Evidence to keep:
- photo of the gauge or the display.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457
Slow filling with the boiler tap
- Who:
- you.
- How:
- pull out the telescopic filling tap under the boiler and turn it slowly anticlockwise, without tools, to 1 to 1.5 bar cold. Open the radiator thermostatic valves first and close the tap afterwards.
- Result that matters:
- the pressure reaches its value without letting in air.
- If it reaches the pressure:
- then bleed the radiators, as Baxi describes.
- If the pressure drops often:
- Baxi says to contact the authorised technical service.
- Evidence to keep:
- photo of the final pressure.
Do not use tools on the tap. If the pressure goes too high, Baxi points to the drain tap at the bottom of the boiler.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457
If E109 stays
- Who:
- you.
- How:
- note when it appears and whether the boiler makes air noises. For 109 Baxi gives no user reset: it says to call the authorised service centre.
- Result that matters:
- whether the code persists with correct pressure and bled radiators.
- If it persists:
- call the authorised technical service.
- If it clears:
- note the date; if it returns, report it anyway.
- Evidence to keep:
- photos of the display with date and time.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457
Inspection by the technician
- Who:
- Baxi authorised technical service.
- How:
- checks the pump operation and its power wiring, as the installer table says.
- Result that matters:
- whether the pump moves the water or air remains in the circuit.
- If the pump is faulty:
- the wiring is repaired or the pump replaced.
- If the pump is fine:
- the circuit is bled and the boiler tested.
- Evidence to keep:
- job sheet with what was checked and replaced.
Baxi says only qualified technicians work on the appliance and that power must be disconnected before any work.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de instalación, montaje y funcionamiento para el instalador 7731458
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Baxi
- Product type
- Gas boiler
Known code variants
- 109
- Baxi 109
- Baxi E 109
- Error 109 Baxi
- Neodens Plus 109
What it means
On the Neodens Plus ECO, code 109 is air present in the boiler circuit and Baxi marks it as a temporary fault. For the user the instruction is to call the authorised service centre. In the installer manual, Baxi says to check the pump operation and its power wiring. Air usually gets in when the system is filled, which is why Baxi asks for slow filling and bleeding the radiators. The code does not separate real air from a pump that is not moving the water.
Warnings and stop conditions
- Criticaleditorial warning
If you smell gas: Baxi says to switch the boiler off, not to operate any electrical device or switch on lights, to put out any flame and open the windows. Then leave the home and call your gas distributor's emergency number and the service centre from outside.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457
- Mediumsource verified
Baxi says to contact the authorised technical service if the pressure drops often: topping up again and again brings fresh air into the circuit.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457
Symptoms and causes
Probable causes · in order
- Air after fillingPossible
Baxi warns that filling fast or with thermostatic valves closed leaves air in the primary circuit. It fits if E109 appears after topping up.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457 · Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de instalación, montaje y funcionamiento para el instalador 7731458
- Pump not working properlyPossible
Baxi tells the technician to check the pump operation. It fits if the pressure is correct and E109 keeps returning without any topping up.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de instalación, montaje y funcionamiento para el instalador 7731458
- Pump power wiringPossible
If the pump gets no power it does not move the water. Baxi tells the technician to check that wiring; the user does not touch it.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de instalación, montaje y funcionamiento para el instalador 7731458
Virtual technician
Does E109 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
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