Vaillant fault code F.086
Fault code F.086 on a Vaillant heat pump (including geoTHERM 3 kW) means: Contact S20 on the heat pump main PCB (HMU) open, incorrect setting of the maximum thermostat, flow temperature sensor (heat pump, gas boiler, system sensor) measures values that deviate downwards. Reset the appliance once. If the code comes back, a part is usually faulty, often a temperature sensor.
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.086 on a Vaillant heat pump indicates: Contact S20 on the heat pump main PCB (HMU) open, incorrect setting of the maximum thermostat, flow temperature sensor (heat pump, gas boiler, system sensor) measures values that deviate downwards.
Applies to
Vaillant geoTHERM 3 kW, VWS 36/4.1 230V.
Fault code F.086 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.086 on aroTHERM Monoblock, VWL 115/2 A 400 V, VWL 155/2 A 400V, VWL 55/2 A 230V, VWL 55/3 A 230 V, VWL 85/2 A 230 V: Floor temperature is too high, flow rate of the heating circuit too low, underfloor heating circuit is closed.
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.
For fault code F.086, the part involved is usually in the category: PCB.
Based on the cause, these original Vaillant parts fit (always check the type number of your appliance):
- Vaillant pressure sensor VHR18-22/3C24-28/3C VHR CW3 4/3 for ecoTEC plus and ecoTEC pro etc. € 20.95
- Vaillant temperature sensor € 31.36
- Vaillant sensor for e.g. aguaFLOW VPM 20/25/2W 0020085154 € 121.53
Further reading on this cause
Other Vaillant codes with the same cause
- F.022 — Water pressure sensor defective, open circuit in the wiring harness, solenoid valve of…
- F.042 — Sensor not connected or sensor input short-circuited
- F.073 — Wire to the water pressure sensor is open circuit or has a short circuit
- F.094 — Flow rate sensor not connected or sensor input short-circuited
- F.1288 — Sensor defective or not correctly connected to the VWZ AI heat pump control module.
- F.514 — Sensor not connected or sensor input short-circuited
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.086 mean?
Contact S20 on the heat pump main PCB (HMU) open, incorrect setting of the maximum thermostat, flow temperature sensor (heat pump, gas boiler, system sensor) measures values that deviate downwards.
How do I fix fault code F.086 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.086?
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.086 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 →