Vaillant S.08 status codewhat it means
Not a fault. S.08 is the burner anti-cycling time: the boiler has just finished a heating burn and is deliberately waiting, up to about twenty minutes, before it is allowed to relight.
Before you start
What S.08 means
S.08 is a status code, shown while the boiler is in "Heating mode: anti-cycling time". Vaillant's installation manuals explain the point of it: "to prevent frequent switching on and off of the burner and thus prevent energy losses, an electronic restart lockout is activated for a specific period each time the burner is switched off", and they add that it "is only active for the heating mode", so a hot tap still fires the boiler straight away.
On the ecoTEC plus and exclusive the display shows the minutes remaining, and the operating instructions list the row as "Heating, remaining anti-cycling time xx mins". How long you wait is not fixed. The installer sets a maximum in diagnostic code D.002, 20 minutes from the factory, and the boiler scales the actual pause to the flow temperature it is aiming for: with the default setting, a 60 °C target gives a wait of about six minutes and a 30 °C target about sixteen and a half, because a cooler system loses heat more slowly and does not need the burner back so soon.
The ecoFIT pure and ecoTEC sustain word the same row as "temporary shutdown after heating procedure", and the 2022 ecoTEC plus shows it as S.008. S.28 is the hot-water twin, the anti-cycling time after a cylinder or comfort-mode burn, and is folded onto this page. Nothing is wrong, nothing needs a reset, and the radiators are still being fed by the pump while the burner rests.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| The burner has just switched off after reaching temperature | The normal case. The flow reached its target, the burner stopped and the anti-cycling timer started. It clears by itself. | Common |
| Flow temperature set low, so the pause is long | Vaillant's table stretches the wait as the target temperature falls. A boiler set to 35 or 40 °C for a well-insulated house will sit in S.08 for a quarter of an hour at a time. | Common |
| The boiler is oversized for the system and short-cycling | If the house never gets warm yet S.08 appears constantly, the burner is heating the small volume of water in front of it in minutes and then being forced to wait. Context, not a Vaillant row. | Occasional |
What to try yourself
Make sure you are reading a status, not a fault. S.08 appears only when the status display is called up; a fault shows F.xx in place of the normal temperature display and stays there. If there is no F code, the boiler has not locked out.
Wait. On the ecoTEC plus the remaining minutes count down on the screen. Hot water is not affected, so run a tap if you doubt the boiler is alive.
If the rooms stay cold while S.08 keeps returning, the boiler is cycling rather than running. Note how many minutes it burns before stopping and give that to your engineer; the flow temperature, the pump speed and the anti-cycling setting are all theirs to adjust.
Get a Gas Safe registered engineer to look at your Vaillant S.08
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 it costs to fix
Typical repair cost
Depends on the cause
Time on site
5 minutes
Nothing. S.08 is normal operation. If the boiler is genuinely short-cycling, adjusting the flow temperature or pump setting is done during a service visit at £80 to £120.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Vaillant fault codes
- S.31Usually simple to fixNot a fault. S.31 is summer mode: heating has been switched off at the boiler while hot water carries on. If you want the radiators back, turn the heating flow temperature up from "Heating off".Related: status codes
- S.30Usually simple to fixNot a fault. S.30 means the room thermostat or programmer is not asking for heat, so the boiler is idle on purpose. If the house is cold, look at the thermostat, not the boiler.Related: status codes
- S.34Usually simple to fixNot a fault. S.34 is frost protection: the boiler has fired by itself because its flow temperature dropped below 5 °C, and it will warm the water to about 30 °C and stop.Related: status codes
- S.40Get it checkedNot a lockout, but not normal either: comfort protection mode. The boiler has detected a fault and is running on with reduced comfort. Its fault memory will say what it found.Related: status codes
- S.88Usually simple to fixNot a fault. S.88 means the purging programme is running: the pump is cycling to push air out of the boiler, 7.5 minutes per circuit, and the burner stays off until it finishes.Related: status codes
- S.96Usually simple to fixNot a fault. S.96, S.97 and S.98 are the boiler testing its own sensors — return, water pressure, flow and return — with heating demands blocked for the few seconds it takes.Related: status codes
Own a Vaillant boiler? Save it and its codes come first next time.
Related guides
Common questions about Vaillant S.08
Can I cancel the anti-cycling time?
The installation manual says a press of the fault clearance key resets the remaining time, and on the ecoTEC plus there is a "Reset anti-cycl. time" menu entry. The operating instructions do not offer either to householders, and the wait exists to save gas and wear, so there is nothing to gain by cutting it short.
Why does it wait longer some days than others?
Because the pause is scaled to the flow temperature the boiler is aiming for. On a mild day with a weather-compensating control asking for 35 °C, the wait with the factory setting is around fifteen minutes; on a cold day at 65 °C it is a couple of minutes.
Is S.28 the same thing?
S.28 is the anti-cycling time after a hot water burn on a boiler with a cylinder or in comfort mode. Same purpose, different circuit. On the 2022 ecoTEC plus both appear with three digits, S.008 and S.028.
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
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.