Vaillant Heating: Compressor shutdownwhat it means
Status S.101, not a fault. Vaillant’s wording is that the heat demand is met, the demand is ended by the system control and the compressor is switched off. The S is the clue.
Before you start
What this means
If the indoor unit is showing "Heating: Compressor shutdown", look at the letter in front of the number. It is S.101, and Vaillant’s appendix of status codes defines it in one sentence: the heat demand is met, the demand is ended by the system control and the heat deficit is offset; the compressor is switched off. That is a heat pump that has done its job and stopped, which is the least alarming thing it can say. The confusion is understandable. Vaillant’s display puts a plain-English description beside every code, and "compressor shutdown" reads like a component failure to anyone who has not met the four families their codes come in.
F codes are faults. S codes are status — the machine narrating what it is doing. M codes are maintenance messages. Comfort protection is reduced running after a permanent fault. S.101 sits in a run of status codes that describes a whole heating cycle: S.100 standby with no demand, S.103 prerun while start conditions are checked, S.104 compressor active, S.101 compressor shutdown when the demand is met, and S.107 overrun while the pump and fan run on for a while after the compressor has stopped. Cooling has the same sequence from S.111 to S.117.
Two neighbours are worth knowing because they look similar and are different. S.102, heating: compressor blocked, means the compressor will not start because the heat pump is outside its operating limits — typically very cold air, or a return temperature that is too high — and that is still not a fault, but it is the unit declining to run rather than finishing. And S.173 is an anti-cycling time imposed by the energy supply company on a restricted tariff. None of these needs an engineer. If the house is cold and the display is cycling through S codes without ever reaching S.104, that is when to ask why.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| The heat demand has been met | Vaillant’s definition of S.101. The system control has ended the demand and the compressor has switched off until the next one. | Common |
| Mild weather and short cycles | In mild weather the demand is met quickly, so S.101 appears often and the display seems to spend its time announcing shutdowns. That is the weather, not the machine. | Common |
| Compressor blocked rather than shut down | S.102 is the different case: the heat pump is outside its operating limits and will not start. Still a status, not a fault, but worth noticing if the house is cold. | Occasional |
What to try yourself
Read the letter. S means status, F means fault. S.101 is the compressor stopping because the demand is satisfied, and it needs nothing from you.
Watch the sequence for a few minutes if you are curious. S.100, S.103, S.104, S.101 and S.107 are one heating cycle from standby to overrun.
If the display shows S.102 and the house is cold, note the outdoor temperature and the time. The compressor is being held off because the heat pump is outside its operating limits, and your installer can tell you whether that is expected for your unit.
Only act on an F code. If the display alternates between a status and an F code, the F code is the one to look up.
Get an F-Gas certified heat pump engineer to look at your Vaillant heat pump
We do not pass enquiries to a repair firm, so there is no form here. When you book an F-Gas certified heat pump engineer, tell them the make, the model and the exact code or message on the display, and ask whether they carry parts for this make — that is what turns one visit into a repair rather than a quote.
What it costs to fix
Typical repair cost
£0
Time on site
5 minutes
Nothing. This is a status message describing normal operation.
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
- Running all the timeUsually simple to fixA heat pump is meant to run long and low. The alarm signal is not the running time, it is the bill — and turning the thermostat up will not warm the house faster.Related: running cost
- F.22Get it checkedWater pressure too low. Vaillant publish exact thresholds and two instructions: the indoor unit manual says inform your competent person; Vaillant UK’s fault page lets a competent owner top up to 1 to 1.5 bar.Related: same brand
- Vapour from the outdoor unitUsually simple to fixA cloud rising off the outdoor unit is the defrost cycle. Vaillant’s own wording is that you do not have to do anything.Related: same brand
- F.511Get it checkedThe sensoCOMFORT controller has lost contact with the heat pump control module. Vaillant give two causes, a defective cable or a plug connection, and the house may stay warm while it shows.Related: same brand
- Sterilisation cycleUsually simple to fixVaillant call it the anti-legionella function: the cylinder is driven above 60 °C on set days, usually at 4 a.m., by the electric back-up heater. It looks like a fault and is not one.Related: same brand
- F.532Get it checkedBuilding circuit flow rate too low, on the earlier aroTHERM monobloc. Vaillant list pressure, blockages, a dirty filter, balancing and air as causes, and send this one to your installer first rather than to Vaillant.Related: same brand
Own a Vaillant heat pump? Save it and its codes come first next time.
Related guides
Common questions
Has the compressor failed?
No. S.101 is Vaillant’s status for the compressor switching off because the heat demand has been met. A failed compressor produces F codes such as F.817, frequency converter fault: compressor, and the heat pump stops rather than narrates.
What is the difference between S.101 and S.107?
Sequence. S.101 is the compressor switching off when the demand ends. S.107 is the overrun that follows, when Vaillant keep the pump and fan running for a while to carry away the remaining heat. You will normally see one and then the other.
Why does my heat pump say compressor blocked?
S.102 means the heat pump is outside its operating limits for heating and will not start the compressor. Vaillant publish the limits by mode; very low outdoor temperatures and a return temperature above 56 °C are the usual reasons. It is still a status code and it clears when conditions change.
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.