- Boilers
- Gas boiler
FA
Junkers FA on a gas boiler: flame still detected after gas shut-off
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Junkers FA means the boiler still sees a flame after the gas has been shut off. It can point to the gas valve, so do not keep resetting: one reset at most and, if it returns, switch off, close the boiler's gas valve and call the technician.
Safety first
Stop and check this first
- FA can mean the gas valve is not closing. If it returns after one reset, switch the boiler off and close the gas shut-off valve until a technician has checked it. Do not open the casing.
- If you smell gas: close the gas shut-off valve, open the windows, do not operate switches, put out any flame and, from outside the home, call the gas company and an authorised installer. If you smell flue gases: switch the boiler off, open doors and windows and call the installer.
Safe checks you can perform
- Gas smell in the boiler room
- A single reset
- Visible condensate drain
- Gas valve shut-off test by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Combustion analysis after the repair
- Do not attempt this professional task: Gas valve tightness and shut-off test
- Do not attempt this professional task: Trap cleaning and electrode check
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.
Combustion analysis after the repair
What they doThe technician measures CO2 or O2 and CO with an analyser and sets the gas/air ratio if needed.
They must show youthe analyser printout.
In writingthe values recorded in the log.
Gas valve tightness and shut-off test
What they doThe technician checks with an instrument that the gas valve shuts off and that no flame remains with the burner stopped.
They must show youthe valve test result.
In writingwhether the valve was replaced and its part number.
Trap cleaning and electrode check
What they doThe technician cleans the condensate trap and checks the electrodes and the ionisation current.
They must show youthe cleaned trap and the ionisation reading.
In writingthe condition of the trap and electrodes.
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.
Gas smell in the boiler room
- Who:
- you.
- How:
- without touching switches, notice whether it smells of gas near the boiler.
- Result that matters:
- whether there is a gas smell.
- If it smells of gas:
- do not reset; follow the gas warning on this page and call from outside.
- If there is no smell:
- go on to the single reset.
- Evidence to keep:
- note the time and what you noticed.
Evidence: Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
A single reset
- Who:
- you.
- How:
- press reset once as Bosch describes.
- Result that matters:
- whether the boiler runs again or FA comes back.
- If FA returns:
- switch the boiler off, close its gas shut-off valve and call the service centre; with this code do not keep trying.
- If it does not return:
- note the date and still tell the technician at the next service.
- Evidence to keep:
- a photo of the display with FA and the three digit number below it.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación
Visible condensate drain
- Who:
- you.
- How:
- without taking anything apart, look at the condensate pipe where it leaves the boiler and where it drains.
- Result that matters:
- whether the pipe drips normally or looks blocked or frozen.
- If it is blocked or frozen at ground level:
- tell the technician; Bosch lists the trap among the causes.
- If it drains well:
- the trap becomes less likely, but only the technician cleans it inside.
- Evidence to keep:
- a photo of the pipe and drain point.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación
Gas valve shut-off test by the technician
- Who:
- authorised gas technician.
- How:
- checks the gas valve, cleans the trap and checks electrodes and flue duct.
- Result that matters:
- whether there is a flame or signal after shut-off.
- If the valve does not close properly:
- that confirms the cause and it is replaced.
- If the valve closes:
- the signal comes from the trap, electrodes or duct.
- Evidence to keep:
- a report with the valve test and what was replaced.
The gas valve, burner and electrodes are for an authorised gas technician only.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
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
- Junkers
- Product type
- Gas boiler
Known code variants
- Cerapur FA
- Error FA Junkers
- F A
- Junkers F A
What it means
On the CerapurComfort, FA means the flame is still detected after the gas is switched off; on the ZWE, that ionisation current remains after the control switches off. Bosch says to check the gas valve, clean the condensate trap and check the electrodes and flue duct. It can be a real flame from a valve that does not close fully or a false signal; the code does not say which.
Warnings and stop conditions
- Higheditorial warning
FA can mean the gas valve is not closing. If it returns after one reset, switch the boiler off and close the gas shut-off valve until a technician has checked it. Do not open the casing.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
- Criticalsource verified
If you smell gas: close the gas shut-off valve, open the windows, do not operate switches, put out any flame and, from outside the home, call the gas company and an authorised installer. If you smell flue gases: switch the boiler off, open doors and windows and call the installer.
Evidence: Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
Symptoms and causes
Probable causes · in order
- Gas valve not closing fullyCommon
Bosch puts the gas valve first in both manuals. If there is a real flame after shut-off, the technician sees it with the burner stopped.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
- Dirty condensate trapPossible
The CerapurComfort asks for the condensate trap to be cleaned for FA. It usually goes with a slow condensate drain or debris in the trap.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico
- Electrodes or flue ductPossible
Bosch also asks to check the electrodes and whether the flue duct is sound. This is the explanation if the valve closes and the trap is clean.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico
Virtual technician
Does FA 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
- 1
Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico
Junkers (Bosch Termotecnia) · 2012 · manual
- 2
Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación
Junkers (Bosch Termotecnia) · 2019 · manual
- 3
Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
Junkers (Bosch Termotecnia) · 2000 · manual
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