Vaillant S.30 status codewhat it means
Not 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.
Before you start
What S.30 means
S.30 is the status Vaillant print as "No heat demand: Controller — room thermostat blocks heating mode". The boiler is healthy and ready; the switched-live or eBUS control wired to it is simply telling it not to run.
On the 2005 to 2012 ecoTEC the table says the same thing in wiring terms, "no heating demand from external controls (clamp 3-4 open)", which is the clearest description of what S.30 actually is: the pair of terminals a room thermostat or programmer closes when it wants heat is open. The ecoMAX and turboMAX plus have the identical row. A related status, S.36, covers the other way a control can hold the boiler off: an analogue or eBUS controller whose target temperature is below 20 °C, or on the older ranges "no heating demand from low voltage controls (clamp 7-8-9)". Both are folded here because the reader's question is the same: why is the boiler not heating when nothing is wrong with it?
Vaillant's troubleshooting table in the operating instructions answers it with "check whether the controller is set correctly", and that is where to start. S.30 is one of the "not firing" statuses alongside S.31, which means heating is switched off at the boiler itself, and S.00, which is plain idleness with no demand anywhere.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Thermostat satisfied or set below room temperature | The room is at or above the set point, or the dial has been turned down. The thermostat opens its contact and the boiler reports S.30. | Common |
| Programmer in an off period, holiday or away mode | Timed controls open the same contact outside their heating periods. A clock that has drifted or lost its schedule after a power cut gives S.30 at odd times. | Common |
| Wireless thermostat lost contact with its receiver | Flat batteries or a pairing lost after a power cut leave the receiver open. The boiler cannot tell the difference between that and a satisfied room. | Occasional |
| eBUS controller target below 20 °C | The S.36 case on the exclusive and 48–64 kW plus: a sensoCOMFORT or VRC control set very low blocks heating mode. Raise the target and the demand returns. | Occasional |
What to try yourself
Confirm there is no F code on the display. S.30 is a status you have called up; if the boiler had locked out you would see F.xx instead of the temperature.
Go to the room thermostat and turn it up well above the room temperature. Most thermostats click or show a flame symbol when they call for heat. Watch the boiler: within a minute it should leave S.30 and run through S.02, S.03 and S.04.
If it does not, check the programmer is in a heating period and not in holiday or off mode, and change the batteries in a wireless thermostat. A receiver that never responds to its thermostat needs the two re-pairing, which the control's own instructions describe.
Get a Gas Safe registered engineer to look at your Vaillant S.30
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
10 minutes
Nothing at the boiler. A replacement wireless thermostat and receiver is £60 to £180 fitted; a call-out to trace a wiring fault £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.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.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.30
The thermostat is up and the boiler still shows S.30.
Then the demand is not reaching the boiler. That is a control or wiring problem rather than a boiler one — a receiver not switching, a broken thermostat or a loose wire at the boiler's terminal block — and an electrician or heating engineer can find it in minutes with a meter.
Does S.30 stop hot water too?
No. It blocks heating mode only. A combi still fires for a tap, and a system boiler still charges its cylinder. If neither of those works either, the problem is not the thermostat.
What is the difference between S.30, S.31 and S.00?
S.30 means an external control is holding heating off. S.31 means heating has been switched off at the boiler, in summer mode. S.00 is simply no demand at this moment, which is what a boiler shows for most of a normal day between burns.
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.