This fault can involve incomplete combustion and carbon monoxide.
If anyone in the property feels sick, dizzy or drowsy, or you can smell gas: open the windows, leave the building, and do not switch anything on or off. Then call the National Gas Emergency Service.
0800 111 999Vaillant F.57 fault codewhat it means and how to fix it
The combustion regulation's measuring programme has found a fault — on the exclusive, a badly corroded ignition electrode; on the 2022 CS/1-5, F.057 means the regulation and its fallback mode have both failed.
Take care
Get a Gas Safe registered engineer to look at your Vaillant F.57
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 F.57 means
F.57 comes from the part of a modern Vaillant that watches its own combustion. On the ecoTEC exclusive and the ..6/5-5 plus table it reads "fault: measuring program — regulation fault caused by corroded ignition electrode", the exclusive adding that the "active comfort protection mode has detected a regulation fault" and the electrode is "highly corroded". The check list is the ignition electrode and the PCB's microcontroller. The board uses the electrode's ionisation current as one of its measurements, and an electrode eaten away by years of sparking gives a reading the regulation cannot work with.
Vaillant's consumer page describes F.57 as "the boiler is not burning correctly in comfort mode" and adds the wider causes — a flue fault or recirculation of flue products, a blocked condensate pipe, low gas pressure, a damaged harness, the PCB, the fan — and gives the householder three checks — gas at other appliances, prepayment credit and ice in an external condensate pipe.
On the 2022 CS/1-5, F.057 is broader: "the combustion regulation has failed and the associated limp home mode has failed", with a check list covering the limp-home history, flue recirculation or blockage, a blocked air intake, condensate in the combustion chamber, gas pressure, the valve offset in D.052, harness, PCB, fan and the air-mass sensor. Because a flue problem is on Vaillant's own list in both places, the page carries the carbon monoxide flag; because the consumer page gives three checks, those are the only steps.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Ignition electrode heavily corroded | Vaillant's named cause on the exclusive and plus tables. The electrode erodes with every ignition and eventually cannot give the regulation a usable signal. | Common |
| Flue recirculation or blockage | First on Vaillant's consumer list and on the CS/1-5 table. Exhaust drawn back into the intake or a restricted flue changes the mixture the regulation is trying to hold. | Occasional |
| Condensate in the combustion chamber | A blocked condensate discharge lets condensate back up around the burner. On the CS/1-5 list with the siphon, the insulating mats and the burner to be checked. | Occasional |
| Gas pressure low, or the valve offset wrong | The consumer page's "gas pressure too low" and the CS/1-5's D.052 offset. The regulation cannot hold a mixture the supply or the valve setting will not allow. | Occasional |
| Board, fan or harness | On every version of the list, and reached last. The exclusive names the PCB microcontroller specifically. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£120–£400
Time on site
1 hour
An electrode with a combustion check is £120 to £180. Flue, condensate or gas supply work depends on what is found; a PCB is £250 to £400.
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.
Vaillant ecoTEC ignition and sensing electrode
0020039221£19–£46Authorised Vaillant parts distributor
Price checked 28 September 2026
Vaillant main PCB (electronics box)
£160–£340Authorised Vaillant parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Vaillant fault codes
- F.56Stop — call an engineerA safety shutdown because the boiler's combustion regulation measured carbon monoxide in the flue gas above its limit. Vaillant say that if it comes back after a reset, the gas valve is defective.Related: combustion control
- F.93Get it checkedVaillant print F.93 as "check gas route": combustion quality is outside the permitted range. The causes are the gas injector, the gas group, flue gas recirculation and a blocked pressure point in the venturi.Related: combustion control
- F.55Get it checkedThe CO sensor — Vaillant's "all-gas sensor" that lets the ecoTEC exclusive regulate its own combustion — is defective or short-circuited. The boiler will not run without it.Related: combustion control
- F.22Get it checkedThe boiler has shut down because there is not enough water in the system. Pressure has dropped below roughly 0.5 bar and it will not fire until you top it up.Related: same brand
- F.75Get it checkedThe boiler cannot detect a rise in pressure when the pump starts, so it has locked out. Usually a failed pressure sensor or a pump that is not moving water.Related: same brand
- F.28Stop — call an engineerThe boiler tried to light and failed every attempt it is allowed — three on an ecoTEC, five on the 2022 CS/1-5 — so it has shut the gas off and locked out.Related: same brand
Own a Vaillant boiler? Save it and its codes come first next time.
Related guides
Common questions about Vaillant F.57
Is F.57 dangerous?
It is a combustion regulation fault and the boiler has stopped itself, which is right. It is not a report of CO in the room. Keep your CO alarm working, do not repeat resets, and have it looked at promptly.
What is "comfort mode"?
Vaillant's name on the exclusive for the regulation that keeps the burner running cleanly on whatever gas quality arrives. F.57 means that regulation has detected something it cannot correct.
How much is an electrode?
A small part. Most of the £120 to £180 is the visit and the combustion check afterwards, which is worth having on a boiler that has reported a regulation fault.
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.