In brief

Fault code F.28 on Vaillant aroTHERM means: Fault code F.28 indicates a burner ignition failure after five initial attempts, causing the appliance to enter fault mode. This fault is also displayed if the problem persists after three manual reset attempts. Most common cause: The burner fails to ignite during the ignition attempt cycles as required by the appliance's safety logic. First action: Check that the gas shut-off valve is fully open.. Call a registered engineer if the fault returns after basic checks or involves refrigerant work (F-Gas registered engineer required).

According to Vaillant service documentation, code F.28 locks the appliance in fault mode after five failed ignition attempts.

F.28 • Vaillant • aroTHERM

Vaillant fault code F.28: causes, diagnosis and solution

Fault code F.28 indicates a burner ignition failure after five initial attempts, causing the appliance to enter fault mode. This fault is also displayed if the problem persists after three manual reset attempts.

Source: Vaillant documentation (service manual – according to product reference) · Updated on 8 June 2026

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What does fault code F.28 on Vaillant mean?

The burner fails to ignite during the ignition attempt cycles as required by the appliance's safety logic.

Symptoms

The burner does not ignite after five attempts.
The appliance does not start and remains locked out.
Fault code F.28 or F.29 is displayed on the screen.
The appliance is in fault mode.

Diagnosis

1. Check the gas supply

Check that the gas shut-off valve is fully open.
Confirm that the fault is indicated by code F.28 or F.29.

2. Reset procedure

Press the reset button to initiate an automatic ignition cycle.
Monitor whether the problem is resolved after three reset attempts.

How to reset fault code F.28 on Vaillant?

If the gas shut-off valve is open, reset the appliance by pressing the reset button for one second. The appliance will attempt another ignition cycle. If the problem persists after three reset attempts, contact a qualified installer.

When should you call an F-Gas engineer?

This code occurs during automatic ignition cycles or after a restart attempt following a fault. It indicates that the standard ignition sequence has failed five times, or that the safety system has locked the appliance after three unsuccessful manual resets, requiring

Affected models

ecotec pro
ecotec plus E
ecotec plus systèmes E
aroTHERM
Vaillant

Field context

Technical source data

Code F.28 signals an ignition failure after five initial attempts, locking the appliance in fault mode (Extract 1). This code also appears if the fault persists after three manual reset cycles (Extract 2). The safety logic prevents start-up until the problem is resolved. To intervene, it is essential to check that the gas shut-off valve is open before resetting via the dedicated button (Extract 1). If three further attempts fail, intervention by a qualified installer is required (Extract 3).

Sources: ecotec pro notice utilisation 0020152380 01 630887 — ecotec-pro-notice-utilisation-0020152380-01-630887.pdf (p. 12) · vaillant notice dutilisation ecotec plus e 0020245021 00 1034572 — vaillant-notice-dutilisation-ecotec-plus-e-0020245021-00-1034572.pdf (p. 15) · vaillant notice dutilisation ecotec plus systmes e 0020245021 00 1034582 — vaillant-notice-dutilisation-ecotec-plus-systmes-e-0020245021-00-1034582.pdf (p. 15)

Frequently asked questions

What is the attempt threshold before code F.28 appears?

Code F.28 is displayed when the burner fails to ignite after five initial attempts, triggering fault mode. This code may also appear if the problem persists after three manual reset attempts performed by the user (Extract 1, Extract 2).

What is the reset procedure for code F.28?

Before resetting, check that the gas shut-off valve is fully open. Then press the reset button for one second to initiate an automatic ignition attempt. If the problem persists after three further attempts, contact an installer (Extract 1, Extract 2, Extract 3).

What should I do if code F.28 reappears after three resets?

If the ignition fault is not resolved after three manual reset attempts, the appliance must be referred to a qualified installer. The extracts explicitly state that the user should not continue reset attempts beyond this threshold without technical assistance (Extract 1, Extract 2, Extract 3).