- Boilers
- Gas boiler
F57
Vaillant F57 boiler fault: comfort mode combustion error
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Fault code F57 (shown as F.57) on a Vaillant ecoTEC boiler means the appliance is not burning correctly in comfort safety mode and its measurement programme failed. Check your gas supply and look for external condensate pipe blockages, try at most one reset, and call a qualified engineer.
Safety first
Stop and check this first
- Because F.57 is a combustion and flame-regulation fault, never open the sealed combustion chamber, clean electrodes yourself, or repeatedly reset the boiler to force it to run.
- If you smell gas or fumes inside the building, open doors and windows immediately, avoid using any electrical switches or naked flames, close the gas emergency control valve if safe, vacate the premises, and call the gas emergency service from outside.
Safe checks you can perform
- Verify gas supply to the property and check the meter
- Visually inspect external condensate pipework for blockages or ice
- Check Live Monitor for status codes S.40 or S.57
- Attempt one single reset on the boiler control panel
Leave these tasks to a qualified professional
- Do not attempt this professional task: Inspect and replace corroded ignition/ionisation electrode and check D.044
- Do not attempt this professional task: Test working gas pressure, flue integrity, condensate trap, and fan/PCB harness
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.
Inspect and replace corroded ignition/ionisation electrode and check D.044
What they doIsolate the appliance, remove and inspect the ignition and flame-sensing electrode for heavy corrosion, fit a new genuine electrode and seal if degraded, and verify the live ionisation value under diagnostic code D.044 (< 400 = good flame, > 800 = no flame).
They must show youThe removed electrode tip condition and the live ionisation reading in diagnostic parameter D.044.
In writingIonisation value recorded in D.044, part number of the replacement electrode and gasket, and successful combustion calibration.
Test working gas pressure, flue integrity, condensate trap, and fan/PCB harness
What they doMeasure dynamic gas inlet pressure at maximum load (20 mbar / 2 kPa on G20 natural gas), clean the internal condensate siphon, test the flue system with a flue gas analyser for recirculation, and inspect the cable harness, fan, and PCB connections.
They must show youGas pressure gauge reading, cleaned condensate siphon, and flue gas analyser combustion printout.
In writingWorking gas pressure in mbar, flue gas CO and CO2 readings, condensate trap check, and harness/fan inspection results.
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.
Verify gas supply to the property and check the meter
- Who:
- you, without tools.
- How:
- Check that other gas appliances in your home are working, confirm the gas isolation valve is fully open, and if you have a prepayment gas meter make sure it has credit.
- Result that matters:
- Rules out a simple gas supply interruption before calling out an engineer.
- If the meter was out of credit or the isolation valve was closed, restore the gas supply before trying a single reset.
- If gas is available at other appliances and the valve is open, move on to the external condensate pipe check.
- Evidence to keep:
- Note confirming gas availability at the meter and other household appliances.
Evidence: Vaillant UK boiler fault codes list · Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
Visually inspect external condensate pipework for blockages or ice
- Who:
- you, by visual inspection from outside without dismantling anything.
- How:
- Check the visible condensate discharge pipe and drain funnel beneath the boiler, paying special attention in cold weather to any externally run plastic pipework that could be blocked by ice.
- Result that matters:
- Identifies whether backed-up condensate is choking combustion.
- If you spot an ice blockage or visible obstruction in the drain line, do not open the boiler casing; arrange for a qualified engineer to clear and check the trap.
- If the condensate drain pipe looks clear and unobstructed, check the status menu on the display.
- Evidence to keep:
- Photo of the external condensate discharge pipe and drain connection.
Evidence: Vaillant UK boiler fault codes list · Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
Check Live Monitor for status codes S.40 or S.57
- Who:
- you, using the display menu buttons.
- How:
- Open Menu and select Live Monitor on the control panel to see whether the appliance logged S.40 (comfort protection mode active) or S.57 (measurement programme waiting period after unsuccessful calibration).
- Result that matters:
- Gives the attending technician exact diagnostic context for the F.57 lockout.
- If S.40 or S.57 was displayed prior to or alongside F.57, note it down for the engineer.
- If only F.57 is shown on the screen, record the exact fault message displayed.
- Evidence to keep:
- Photo of the Live Monitor screen and fault display.
Evidence: Vaillant ecoTEC exclusive VMW ..6/5-7, instrucciones de instalación y mantenimiento 0020198146_03 · Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
Attempt one single reset on the boiler control panel
- Who:
- you, pressing the fault clearance key once.
- How:
- Press the fault clearance (reset) button once for 1 second and wait to see whether the boiler completes its measurement cycle and lights cleanly.
- Result that matters:
- Clears a one-off combustion calibration hiccup without stressing the ignition system.
- If the fault clears and heating and hot water run smoothly, keep an eye on the display over the next few days.
- If F.57 returns after that single reset, do not press reset repeatedly; contact your installer or Vaillant service solutions.
- Evidence to keep:
- Record of the single reset attempt and the returning F.57 code.
Evidence: Vaillant UK boiler fault codes list · Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
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
- Vaillant
- Product type
- Gas boiler
Known code variants
- caldera Vaillant F.57
- ecoTEC F57
- error F57 Vaillant
- F.57
- Vaillant ecoTEC F57
- Vaillant F57
- Vaillant fault code F.57
What it means
On Vaillant ecoTEC boilers, fault code F.57 indicates that active comfort safety mode has detected a combustion regulation error during the measurement programme (associated with status codes S.40 and S.57 in the Spanish ecoTEC exclusive manual). The code alone never proves the PCB, fan, or electrode has failed, because low incoming gas pressure, a frozen or blocked condensate discharge pipe, or flue gas recirculation can prevent combustion calibration.
Warnings and stop conditions
- Highsource verified
Because F.57 is a combustion and flame-regulation fault, never open the sealed combustion chamber, clean electrodes yourself, or repeatedly reset the boiler to force it to run.
Evidence: Vaillant UK boiler fault codes list · Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
- Highsource verified
If you smell gas or fumes inside the building, open doors and windows immediately, avoid using any electrical switches or naked flames, close the gas emergency control valve if safe, vacate the premises, and call the gas emergency service from outside.
Evidence: Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
Symptoms and causes
Probable causes · in order
- Heavy corrosion or wear on the ignition and flame-sensing electrodeCommon
Severe corrosion or deposits on the ignition/ionisation electrode distort the flame signal during the automatic measurement programme, triggering a regulation lockout.
Evidence: Vaillant ecoTEC exclusive VMW ..6/5-7, instrucciones de instalación y mantenimiento 0020198146_03
- Blocked condensate discharge pipe or flue gas recirculationCommon
An ice blockage or restriction in the condensate drain pipework, or a flue fault causing combustion products to recirculate into the air intake, disrupts burner stability in comfort mode.
Evidence: Vaillant UK boiler fault codes list · Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
- Gas supply pressure too low or interrupted at the meterPossible
Insufficient gas inlet pressure, a partly closed isolation valve, or a prepayment meter out of credit starves the burner during calibration.
Evidence: Vaillant UK boiler fault codes list · Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
- Damaged cable harness, defective fan, or faulty main PCBLess common
A wiring fault on the electrode or gas-air control harness, a failing combustion fan, or a defective main circuit board prevents accurate flame regulation.
Evidence: Vaillant UK boiler fault codes list
Virtual technician
Does F57 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
Vaillant UK boiler fault codes list
Vaillant Group · 2026 · official_doc
- 2
- 3
Vaillant ecoTEC exclusive VM y VMW ..6/5-7, instrucciones de funcionamiento 0020196912_02
Vaillant · 2016 · manual
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