Vaillant fault code F.742
Fault code F.742 on a Vaillant heat pump (including flexoTHERM) means: Inlet temperature in the ambient circuit too high for compressor start, brine inlet temperature > 50 °C, supply of external heat into the ambient circuit. Reset the appliance once. If the code comes back, a part is usually faulty, often the compressor or inverter module. You can check the water pressure and settings yourself; leave work on gas-carrying parts to a certified gas engineer.
After a safety alert (gas, flue gas, combustion), reset no more than once and call in a certified gas engineer. If you smell gas, call your national gas emergency number or 112 immediately.
Cause
Fault code F.742 on a Vaillant heat pump indicates: Inlet temperature in the ambient circuit too high for compressor start, brine inlet temperature > 50 °C, supply of external heat into the ambient circuit.
Applies to
Vaillant flexoTHERM, VWF 117/4, VWF 157/4, VWF 197/4, VWF 57 /4, VWF 87/4, flexoCOMPACT exclusive, VWF 118/4.
Fault code F.742 on other Vaillant series
The same code does not mean the same thing on every series. Check the rating plate to see which series you have:
- F.742 on geoTHERM 3 kW, VWS 36/4.1 230V: Inlet temperature in the ambient circuit too high for compressor start - Heating: air inlet temp. > 25 °C, Cooling: air inlet temp. > 37 °C.
Matching parts
Vaillant parts are available from Instalpunt; shipping to EU countries from €17.95 (€24.95 for more distant countries), usually 3–5 working days.
Parts by Vaillant series: ecoTEC plus · ecoTEC pro.
Based on the cause, these original Vaillant parts fit (always check the type number of your appliance):
- Vaillant compressor for e.g. flexoTHERM VWF 58/4 0020210662 € 2,059.52
- Vaillant compressor for e.g. flexoTHERM VWF 87/4 0020210663 € 2,093.49
- Vaillant compressor for e.g. flexoTHERM VWF 117/4 0020210664 € 2,573.09
Further reading on this cause
Other Vaillant codes with the same cause
- F.103 — Parameter ""Max. duration of the circuit breaker"" is set incorrectly (see ""Heat pump…
- F.1117 — Soft starter defective or incorrectly connected, fuse defective, poorly tightened…
- F.514 — Temperature sensor at compressor inlet defective or not connected
- F.517 — Temperature sensor at compressor outlet defective or not connected
- F.726 — Compressor overheated, e.g. due to use outside its application limits, maximum ambient…
- F.729 — Compressor outlet temperature lower than 0 °C for more than 10 minutes or compressor…
Fix it yourself or call an engineer?
Always consult the manual for your appliance and work safely. If in doubt or if the fault comes back, call in a qualified professional. A question about a part? Write to us at info@instalpunt.nl.
Frequently asked questions
What does Vaillant heat pump fault code F.742 mean?
Inlet temperature in the ambient circuit too high for compressor start, brine inlet temperature > 50 °C, supply of external heat into the ambient circuit.
How do I fix fault code F.742 on a Vaillant heat pump?
First check the cause described above. Then restart the appliance using the reset button. If the message comes back, a part usually needs replacing or the fault needs to be repaired by a qualified professional.
Which parts do I need for Vaillant fault code F.742?
That depends on the exact cause. In the Vaillant parts overview at Instalpunt you will find the current price and stock for each part.
Can I fix fault code F.742 myself?
You can reset the appliance and check things like the water pressure or settings yourself. Work on gas-carrying parts must be left to a certified gas engineer.
All Vaillant heat pump faults and codes at a glance →