Vaillant Running all the timewhat to check
A 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.
Before you start
What this means
This is the commonest complaint about a working heat pump, and it comes from a reasonable place. A gas boiler fires hard, gets the house up to temperature, and shuts off, so the sound of it cycling is the sound of it working. A heat pump does the opposite. It produces heat most efficiently when it runs gently and continuously, extracting a small temperature lift from the outside air over hours rather than blasting the house up in twenty minutes.
A household that has just switched over hears constant running and reads it as a machine struggling. It is not; it is the design. The same misreading produces three related complaints. Radiators that feel merely warm rather than hot are weather compensation doing its job — the system chooses a flow temperature to suit the outside conditions, and a lower flow temperature is both cheaper and more effective over a day. Turning the thermostat up does not make the house warm faster, because the system is already delivering as much as the compensation curve allows; it just changes the target it eventually reaches. And the circulation pump running while nothing appears to be heating is normal, and Panasonic publish it as such on their own support material. There is also a case where the running time genuinely is telling you something, and it is worth separating out.
Vaillant publish an instruction people ask about every winter and get wrong: ensure the heating installation always remains in operation during freezing conditions and that all rooms are sufficiently heated, and if you cannot ensure that, have a competent person drain the installation. In other words, do not switch a heat pump off at the isolator when you go away in January. Use holiday mode, which keeps frost protection alive. What is a real signal is cost rather than runtime. If the running has not changed but the bill has stepped up, that points at the backup immersion heater quietly taking over the load, which keeps the house warm and roughly doubles what it costs to do so.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Normal continuous operation | The design intent. A heat pump is most efficient running long and low, so hours of quiet running is the machine working properly rather than struggling. | Common |
| Weather compensation running cooler radiators | The system picks a flow temperature to suit the outside conditions. Radiators you can hold your hand on are the expected result, not an underperforming system. | Common |
| A house that loses heat faster than expected | Genuine, and not a fault in the heat pump. A system sized on optimistic assumptions about insulation or draughts will run flat out in cold weather and still not quite get there. | Occasional |
| The backup heater carrying the load | The case that actually costs money. The house stays warm, the running looks normal, and the electricity consumption steps up sharply because an immersion element is doing the work. | Occasional |
What to try yourself
Check whether the house is actually reaching the temperature you asked for. If it is, long running is the system working rather than failing.
Resist turning the setpoint up to speed things along. It will not heat the house faster and on many systems it costs more, because a higher flow temperature is less efficient.
Compare your electricity use against the same period last year rather than against your intuition. A step change is the signal worth acting on; long runtime on its own is not.
If you are going away in winter, use holiday mode rather than switching the system off.
Vaillant publish the reason: the heating installation must remain in operation during freezing conditions with all rooms sufficiently heated, and if that cannot be ensured the installation should be drained by a competent person. Isolating a heat pump in January risks freezing the water side.If your consumption has stepped up without a code, ask your installer to check whether the backup or immersion heater is running and what is calling it. That is a specific question with a specific answer.
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
15 minutes
Nothing. This is how a heat pump is designed to work. A visit is only worth booking if the cost has changed, not if the runtime has.
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
- Heating: Compressor shutdownUsually simple to fixStatus 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.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
Should my heat pump ever switch off?
It will cycle off in mild weather and when the house is up to temperature, but in cold weather running for hours at a time is normal and efficient. Judging a heat pump by how often it stops is applying boiler logic to a machine that works the other way round.
My radiators are never hot. Is the system undersized?
Probably not. Weather compensation deliberately runs a lower flow temperature when it can, which makes radiators warm rather than hot and makes the system cheaper to run. The question to ask is whether the house reaches the temperature you set, not whether the radiators are too hot to touch.
The pump is running but nothing seems to be heating.
That is documented normal behaviour rather than a fault — Panasonic publish the circulation pump running while nothing is heating as expected on their systems. The pump also runs during defrost cycles and for anti-seize routines that some manufacturers schedule deliberately.
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
- Manufacturer support portal
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.