Vaillant F.718 fault codewhat it means and how to fix it
Fan unit blocked: the outdoor unit has no confirmation that its fan is turning. Vaillant’s remedy is to check the air route and clear blockages, after four failed restarts fifteen minutes apart.
Take care
What F.718 means
F.718 is the outdoor unit reporting that its fan is not turning. The appendix wording is "Fan unit 1: Fan blocked — there is no confirmation signal stating that the fan is rotating", and on twin-fan units the second fan has its own code, F.785.
Vaillant’s remedy is a single line: check the air route and, if required, remove any blockages. The path to the fault is published too, in the status code S.252 that precedes it: if the fan speed is 0 rpm, the heat pump is switched off for 15 minutes and then restarted, and if the fan does not start after four unsuccessful restarts the heat pump is switched off and F.718 is displayed. That sequence matters for safety as much as diagnosis, because it means an outdoor unit showing a fan fault has been trying to spin that fan every quarter of an hour, and will try again.
Vaillant UK’s owner page lists the causes: damage or blockage to the fan blade, a faulty fan motor, a fault in the electrical connection to the motor, an HMU fault and an installer board fault. Of those, only the first is anything an owner can see. The everyday causes are a build-up of ice on the blades after a defrost that did not clear, drifted snow, leaves packed against the grille, a stick through the guard, a bird’s nest, or something stacked against the unit over the summer. If the grille is clear and the fan still does not turn, it is the motor or the electronics, and both are inside the casing.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Ice, snow or debris on the fan | Vaillant’s only published remedy is to clear the air route, which tells you where they expect the problem to be. Ice after a failed defrost is the winter version; leaves and nests the rest of the year. | Common |
| Fan blade damaged | Named by Vaillant UK. A blade chipped by ice or a foreign object can jam or trip the motor’s protection. | Occasional |
| Fan motor or its wiring failed | Vaillant name the motor and its electrical connection. Reached once the air route has been proven clear. | Occasional |
| HMU or installer board fault | The electronics that drive and monitor the fan. The least common outcome and an engineer diagnosis. | Occasional |
What to try yourself
Switch the outdoor unit off at its isolator before you go near the grille. The unit tries to restart the fan every fifteen minutes, and a fan that is jammed by debris will start the moment the debris moves.
Never reach through the guard or put anything into it while the unit is live. Isolate first, every time.Look through the grille for what is stopping it — ice on the blades, packed snow or leaves, a stick, a nest. Clear what you can reach from outside the guard, and clear anything stacked against the unit or growing around it.
If it is ice, let it melt. Do not pour hot water on the unit or chip at the blades; the coil behind the fan carries refrigerant and the fins are thin aluminium.
Restore power and let the unit try again. If F.718 returns with a clear air route, book your installer — the motor, its wiring and the boards are theirs.
Get an F-Gas certified heat pump engineer to look at your Vaillant F.718
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–£400
Time on site
20 minutes
Nothing if the air route was blocked. An installer visit is typically £90 to £180, and a replacement fan motor on the outdoor unit runs to £250 to £400 fitted.
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
- 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
- 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: 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 about Vaillant F.718
The fan is visibly free and clean but the code is still there.
Then the fan is not blocked, it is not being driven or not being seen. Vaillant name the motor, its electrical connection, the HMU and the installer board. Those are inside the casing and the visit is the installer’s.
Why did the heat pump take an hour to show the code?
Because of the published sequence. At zero fan speed the unit stops for fifteen minutes and retries, and only after four failed attempts does it lock out with F.718. During that hour the status code S.252 was showing instead.
Can I run the heating while I wait?
The heat pump will not run without its fan, but the electric back-up heater may take over depending on configuration, so the house need not go cold. Expect the electricity meter to reflect that until the fan is fixed.
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.