Vaillant S.88 status codewhat it means
Not 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.
Before you start
What S.88 means
S.88 is the status "Purging programme is running — the purge programme is activated", or on the ecoFIT pure and ecoTEC sustain simply "product purging active". It is check programme P.00, and the ecoTEC plus manual describes what it does: "the internal pump is cyclically actuated. The heating circuit and the domestic hot water circuit are adaptively purged by automatically switching the circuits using the automatic air vent (the automatic air vent's cap must be loose). The active circuit is shown in the display … The purge programme runs for 7.5 min per circuit and then terminates."
So a boiler in S.88 is not trying to light. Its pump runs in bursts, the diverter valve swaps between heating and hot water sides, and the air that filling or a repair left in the boiler is pushed to the automatic air vent and out. The display shows the filling pressure meanwhile, because the manual also asks the installer to "make sure that the filling pressure of the heating installation does not fall below the minimum filling pressure" as the air leaves and the water level drops.
The programme is started by hand from the installer level, usually at commissioning or after the system has been drained and refilled, which is why householders mostly meet S.88 in the hour after an engineer has left. It ends by itself, 7.5 minutes per circuit, or when it is cancelled. S.108, which the ecoFIT and sustain add, is a different purge — "purging the combustion chamber, fan in operation" — where the fan runs the burner chamber clear before an ignition attempt; it lasts seconds and is folded here because readers search both as "purging". The 2022 ecoTEC plus shows S.088.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Engineer started P.00 after filling or a repair | The normal case. The system has just been refilled and the purge is clearing air from the boiler. Vaillant give 7.5 minutes per circuit, so about fifteen for a combi's two. | Common |
| Combustion chamber purge before ignition | The S.108 form on the ecoFIT and sustain: the fan runs to clear the chamber before every ignition attempt. Brief and automatic. | Common |
| Purge repeated because air remained | The manual says that if there is still too much air at the end of P.00 the programme is repeated. A second run is not a fault. | Occasional |
What to try yourself
Leave it to finish. There is no reset and nothing to press; the boiler returns to its normal display when the programme ends and will then respond to heat demands.
Watch the pressure it shows while purging. If it falls toward 1 bar as air leaves, top the system up afterwards as the operating instructions describe, then bleed any radiator that is cold at the top.
If S.88 appears with no one having touched the boiler and keeps recurring, mention it at the next service. It should only run when started.
Get a Gas Safe registered engineer to look at your Vaillant S.88
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
15 minutes
Nothing. The purge is part of commissioning or a repair visit and is not charged separately.
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.08Usually simple to fixNot 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.Related: status 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.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.88
Is S.88 a fault?
No. It is a check programme running. Vaillant list it among the status codes, and it ends by itself after 7.5 minutes per circuit.
The heating will not come on while it shows.
Correct. The manual says "the product does not start up" while P.00 runs; the burner is held off so the pump can move air rather than heat. Demands are honoured again the moment it finishes.
Can I start it myself to get air out of the system?
It is in the installer level, behind the access code, and the operating instructions do not offer it. Bleeding the radiators is the householder's way of removing air; the purge programme is for air trapped inside the boiler itself.
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.