Vaillant heat pump fault codes

Vaillant aroTHERM heat pumps show faults as F followed by a number, with a plain-English explanation beside it. Not everything on the display is a fault: S-codes are normal running states and M-codes are maintenance messages where the unit keeps working. If yours is an aroTHERM plus, it runs on propane, and that brings an obligation most owners are never told about.

Where the code shows on a Vaillant

Vaillant run four separate families and only one of them is a fault. F codes are faults and take priority over everything else on the display; where several occur at once they alternate every two seconds. S codes are status codes describing normal operation. M codes are maintenance messages — attention needed, unit still running. And comfort protection mode means the system has reduced what it is doing rather than stopped. Note the leading zero: the same low pressure fault is printed as F.22 in owner-facing text and F.022 in the appendix, so a search for one may not find the other — and the troubleshooting section of the uniTOWER plus and hydraulic station operating instructions heads the same fault F.723, so that form turns up too. Which table you are reading depends on the generation. The aroTHERM plus (R290, VWL /6) and the aroTHERM split (R410A, VWL /5) share one table, with faults running to three or four digits — F.514, F.820, F.1120 — that lives in the indoor unit’s manual rather than the outdoor unit’s. The earlier aroTHERM monobloc (R410A, VWL /2) has a shorter table of its own, where the fan fault is F.037, low flow is F.532 and the eBUS fault is F.685, and none of the F.7xx, F.8xx or F.11xx codes exist. Two more sources of confusion: the sensoCOMFORT controller has a fault table of its own, so F.509 and F.511 are the controller reporting a component it cannot hear rather than a heat pump fault, and the wireless VRC 720f adds plain-text messages such as "Radio communication interrupted". There is no E-prefixed code anywhere in Vaillant’s heat pump documentation.

How to reset a Vaillant

There is a reset button on the indoor unit — on the uniTOWER plus and hydraulic station it is the round button on the control panel behind the front flap — and Vaillant UK tell owners to use it. Their published procedure: press and hold the reset button for three seconds, allow five minutes for the heat pump to restart, try a second time only if it has not, and perform the reset no more than twice; if the fault continues, contact your installer or Vaillant technical support. The installer instructions say the same thing from the other side: eliminate the fault, press the reset button to start up again, and if the fault recurs despite several reset attempts, contact Customer Service. Two things temper that. Vaillant publish a limp home mode, so depending on the fault the system may keep providing heating or hot water at reduced capability rather than stopping, and a live fault code does not always mean a cold house — check whether you actually have heat before treating it as an emergency. And the fault memory holding the last ten faults, and the ability to clear it, sit in the installer menu rather than the owner one, so a code that keeps coming back is evidence for the engineer rather than something to keep clearing.

Most common Vaillant faults

The Vaillant codes people look up most.

Every Vaillant fault code

17 published codes. Filtering happens in the page — every one is in the HTML.

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Showing 17 of 17 codes

Every published Vaillant fault code with its meaning and severity
Code	What it means	Severity
F.22	Water 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.	Get it checked
Vapour from the outdoor unit	A cloud rising off the outdoor unit is the defrost cycle. Vaillant’s own wording is that you do not have to do anything.	Usually simple to fix
Running all the time	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.	Usually simple to fix
F.511	The 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.	Get it checked
Sterilisation cycle	Vaillant 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.	Usually simple to fix
F.532	Building 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.	Get it checked
Radio communication interrupted	A message from the wireless sensoCOMFORT VRC 720f, not from the heat pump. Vaillant’s first instruction is to make sure the power supply is on; the second concerns reception strength.	Get it checked
Protective zone	aroTHERM plus runs on propane. Vaillant define a zone around the outdoor unit where you may not add sockets, lights, vents or openings — and the duty is yours.	Stop — call an engineer
F.788	The building circuit pump has detected a fault of its own and locked itself off. Vaillant’s first remedy is a thirty-second power-off, and the causes include dry running and a blocked filter.	Get it checked
F.820	Connection fault on the building circuit pump: the pump is not reporting any signal back to the heat pump. Vaillant’s remedy is the cable first and the pump second.	Get it checked
F.718	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.	Get it checked
F.9998	The heat pump has lost its eBUS connection to the controllers and wiring centre. Vaillant name an unconnected or miswired eBUS cable and an outdoor unit without supply voltage as the causes.	Get it checked
F.1120	Phase failure on the electric back-up heater: its internal circuit breaker has opened. Vaillant say the competent person resets it, and warn the anti-legionella function is not guaranteed meanwhile.	Get it checked
F.1100	The safety cut-out on the electric back-up heater has opened. Vaillant name low flow, air, a heater run on an unfilled circuit, a trip above 89 °C that needs a new fuse, and external heat.	Get it checked
F.821	Sensor fault on the immersion heater flow temperature. Vaillant give a disconnected or short-circuited sensor, or both flow sensors failed, and the fix is a sensor or a cable harness inside the indoor unit.	Get it checked
Heating: Compressor shutdown	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.	Usually simple to fix
E5	E5 is not a Vaillant heat pump code. Vaillant’s aroTHERM, uniTOWER and sensoCOMFORT fault tables run F.5xx to F.9998, so an E5 on your display belongs to something else in the system.	Usually simple to fix

Vaillant models

Codes can differ between generations. Check yours.

Guides that help with Vaillant faults

Looking for Vaillant’s own support? www.vaillant.co.uk. We are not affiliated with Vaillant.