Vaillant F28 Error: Ignition Failure and How to Fix It
Independent guide — no official affiliation with the platforms mentioned.
Réponse courte
Vaillant F28 means 'ignition failure' — the boiler can't light the gas. Usually the gas valve is closed or there's a gas outage. Check the valve, reset the boiler; if it persists, the ignition electrode needs service.
01 — Solution étape par étape
Solution étape par étape
STEP 01
Check that the gas valve is open
The valve handle under the boiler should be parallel to the pipe. If it's perpendicular, open it.
If you smell gas: close the valve, don't touch electrical switches, leave the building and call the gas utility. Skip the steps below.
STEP 02
Check for a gas outage
Try another gas appliance, like the stove. If nothing lights, there may be an outage — wait a few minutes and retry.
STEP 03
Reset the boiler
Hold the reset button on the front panel for 2–3 seconds. The boiler retries ignition.
STEP 04
Check the water pressure
System pressure should read 1.0–1.5 bar. Refill via the filling loop if it's low.
STEP 05
Call service if it fails 3 times
If F28 returns after reset, the ignition electrode, gas valve or ionization measurement needs professional inspection.
Conseils
- After long disuse, 2–3 resets may be needed to purge air from the gas line.
- Skipping annual service accelerates electrode fouling — the second most common F28 cause.
02 — Questions fréquentes
Questions fréquentes
Does F28 go away by itself?
If it was caused by a gas outage, yes — reset after supply returns. Dirty electrodes cause recurring F28s that need service.
F28 vs F75 — what's the difference?
F28 is ignition (gas); F75 is a pressure sensor/pump fault. In F28 the boiler can't light; in F75 it lights but pressure readings are inconsistent.
Why does F28 appear in freezing weather?
In condensing models the condensate drain can freeze and lock the gas valve. Check that the drain's heating cable works.
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