Vaillant F.323 fault codewhat it means and how to fix it
The heating pump in a 2022 ecoTEC plus is dry running — turning with no water in it. Vaillant name air in the boiler as the cause; a pump run dry may need replacing.
Take care
Get a Gas Safe registered engineer to look at your Vaillant F.323
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 F.323 means
F.323 is "the heating pump is dry running", and Vaillant give two lines beneath it: "air in the product — purge the heating installation", and "pump has been dry-running — replace the pump". A wet-rotor pump is cooled and lubricated by the water it moves. Run it in air and the rotor spins in nothing, the bearings heat and the pump electronics can tell from the motor's behaviour that there is no load on it.
The CS/1-5's pump reports that state and the boiler stops before damage is done, which is why the first remedy is simply to get the air out. Air gets into a sealed system in two ways: through low pressure, when a leak has let the water level in the boiler fall until the pump sits in an air pocket, or through the filling and venting of a new or recently drained system that was never properly purged.
Low pressure is something the CS/1-5 reports separately as F.022, so an F.323 on its own usually means air trapped high in the boiler or the pipework with the pressure still reading normally. The second line is the warning: a pump that has run dry for long enough may already be damaged, and Vaillant's table allows for replacing it. There is one householder check, taken from the CS/1-5 operating instructions' filling-pressure section, before an engineer is needed.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Air trapped in the boiler | Vaillant's first cause. An air pocket at the pump after filling, draining or a pressure drop. Purging the installation is the remedy. | Common |
| System pressure fallen | A leak or a discharged expansion vessel lets the water level fall until the pump sees air. Usually reported as F.022 first; if not, check the gauge. | Common |
| Pump damaged by running dry | Vaillant's second line. Bearings that have run without water may be worn, and the pump reports dry running even when the circuit is full. | Occasional |
| Automatic air vent stuck | The boiler's own air separator cannot release air it has collected. Context rather than Vaillant's wording; checked during the purge. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£80–£320
Time on site
45 minutes
Purging the boiler is a call-out of £80 to £120. A pump damaged by dry running is £250 to £320 fitted.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Expansion vessel (8 litre, sealed system)
EV-8L£35–£85Plumbing merchant
Price checked 28 September 2026
Central heating circulating pump
CH-PUMP-15-60£90–£180Plumbing merchant
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Vaillant fault codes
- F.325Get it checkedThe heating pump in a 2022 ecoTEC plus has reported a fault — blocked, or defective. F.320, F.321, F.324 and F.330 are its neighbours in the same pump family, and this page covers them too.Related: pump and hydraulics
- F.89Get it checkedThe pump is not connected, is connected incorrectly, or is not the pump the boiler expects. On the 2022 CS/1-5, F.089 means the fitted pump does not match the unit type.Related: pump and hydraulics
- F.322Get it checkedThe heating pump in a 2022 ecoTEC plus has overheated, and running it more gently did not bring the temperature down. Vaillant's remedy is to check and if necessary replace the pump.Related: pump and hydraulics
- F.94Get it checkedThe vortex and differential pressure sensors — the two that measure flow through the heat exchanger on an ecoTEC plus or exclusive — are returning values the board does not believe.Related: pump and hydraulics
- F.22Get it checkedThe boiler has shut down because there is not enough water in the system. Pressure has dropped below roughly 0.5 bar and it will not fire until you top it up.Related: same brand
- F.75Get it checkedThe boiler cannot detect a rise in pressure when the pump starts, so it has locked out. Usually a failed pressure sensor or a pump that is not moving water.Related: same brand
Own a Vaillant boiler? Save it and its codes come first next time.
Related guides
Common questions about Vaillant F.323
I bled the radiators. Is that enough?
Sometimes. Bleeding radiators releases air from the high points of the system, but the air Vaillant mean here is in the boiler, around the pump, and that has to be purged at the boiler. If the code returns after bleeding, it needs an engineer.
Why did it not show F.022?
F.022 is low pressure measured by the pressure sensor. F.323 is the pump finding air regardless of what the gauge says. A system can hold pressure and still have an air pocket exactly where the pump is.
Will the pump need replacing?
Not if the air is cleared quickly. Vaillant allow for a replacement where the pump has run dry for a while; an engineer will judge from how it sounds and performs once the circuit is full.
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.