Vaillant Vaillant uniTOWER plus and hydraulic station fault codes
The indoor units paired with aroTHERM plus: uniTOWER plus with its integrated 190-litre cylinder, and the wall-hung hydraulic station VWZ MEH 97/6. The display, the reset button, the electric back-up heater and the F.5xx to F.1120 fault appendix all live here.
Codes on the Vaillant uniTOWER plus and hydraulic station follow the same Vaillant scheme as the rest of the range. Where a code behaves differently on this generation, the code page says so.
Vaillant fault codes
Every published Vaillant code. Open a code to see which models and years it applies to.
- F.22Water 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 unitA 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 timeA 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.511The 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 cycleVaillant 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.532Building 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 interruptedA 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 zonearoTHERM 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.788The 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.820Connection 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.718Fan 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.9998The 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.1120Phase 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.1100The 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.821Sensor 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 shutdownStatus 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
- E5E5 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