Vaillant Heat Pump Fault Codes Explained: Troubleshooting & Fixes (2024)

Written by

Adam Raw

A picture of the Vaillant manufacturing plant with an engineer doing work on an Arotherm Plus, with the text fault codes

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Introduction:

Vaillant produces highly efficient and reliable heat pumps, making them popular for home heating systems. However, they can experience issues that trigger fault codes. These fault codes can help diagnose problems with the unit, allowing homeowners and technicians to identify and resolve the issues quickly.

In this comprehensive guide, we’ll explain common Vaillant heat pump fault codes, particularly for models like the Vaillant aroTHERM Plus. We’ll cover what each code means, possible causes, and how to fix them. If your Vaillant heat pump is displaying an error, keep reading for expert troubleshooting tips.

What Are Vaillant Heat PumpFault Codes?

The Vaillant aroTherm Plus heat pump has a built-in diagnostic system that displays fault codes whenever something goes wrong. These codes can help you pinpoint problems, reducing repair time or allowing you to resolve the issue yourself. Some faults are relatively easy to fix with basic troubleshooting, while others require professional servicing.

Common Vaillant Heat Pump FaultCodes Explained

Here are some of the most common Vaillant aroTherm Plus fault codes, their meanings, and possible solutions:

F.022 - Water Pressure Too Low: This code indicates that a pressure drop is present in the heating circuit. Top up the system with water and check for leaks.
F.042 - Coding Resistor Fault: The coding resistor might be missing or it might be incorrectly installed. Inspect its placement and replace if necessary.
F.514 - Compressor Inlet Temperature Sensor Fault: This usually means the sensor is faulty or disconnected. Reconnect or replace the sensor.

For a full breakdown of all Vaillant fault codes, including causes and remedies, refer to the detailed fault code table below.

Code	Meaning	Cause	Remedy
F.022	Water pressure too low	Pressure loss in the building circuit due to leakages or air pockets; Building circuit pressure sensor defective	Check for leaks; Top up with water, purge; Verify sensor wiring; Replace pressure sensor if needed
F.042	Fault: Coding resistor	Coding resistor damaged or not set	Check coding resistor position; Replace if needed
F.073	Sensor fault: Build. circ. pressure	Sensor not connected or input short-circuited	Check and replace the sensor; Replace cable harness
F.094	Fault: Vortex	Volume flow sensor not connected or sensor input short-circuited	Check and replace sensor; Replace cable harness
F.103	Fault: Spare part ident.	Incorrect control PCB installed on the outdoor unit	Install the correct PCB
F.514	Sensor fault: Compr. inlet temp.	Sensor not connected or input short-circuited	Check and replace sensor; Replace cable harness
F.517	Sensor fault: Compr. outlet temp.	Sensor not connected or input short-circuited	Check and replace sensor; Replace cable harness
F.519	Sensor fault: Building circuit return temp.	Sensor not connected or input short-circuited	Check and replace sensor; Replace cable harness
F.520	Sensor fault: Building circuit flow temp.	Sensor not connected or input short-circuited	Check and replace sensor; Replace cable harness
F.526	Sensor fault: EEV outlet temp.	Sensor not connected or input short-circuited	Check and replace sensor; Replace cable harness
F.546	Sensor fault: High pressure	Sensor not connected or input short-circuited	Check the sensor and replace if necessary; Replace cable harness
F.582	Fault: EEV	EEV not connected correctly or cable break	Check plug connections; Replace EEV coil if required
F.585	Sensor fault: Capac. outlet temp.	Sensor not connected or input short-circuited	Check and replace sensor; Replace cable harness
F.703	Sensor fault: Low pressure	Sensor not connected or input short-circuited	Check sensor and replace if necessary; Replace cable harness
F.718	Fan unit 1: Fan blocked	No confirmation signal from fan	Check air route; Remove blockages
F.729	Compressor outlet temperature too low	Compressor outlet temperature is lower than 0°C for more than 10 minutes	Check high-pressure sensor; Inspect EEV operation; Check for refrigerant overfilling
F.731	High-pressure switch open	Refrigerant pressure too high	Purge building circuit; Inspect pressure sensor; Reset manually
F.732	Compressor outlet temperature too high	Application limits exceeded	Check compressor inlet/outlet sensors; Inspect refrigerant volume
F.733	Evaporation temperature too low	Insufficient air volume flow through the outdoor unit's heat exchanger	Check fan unit for dirt; Inspect EEV operation; Check refrigerant volume
F.734	Condensation temperature too low	Heating circuit temperature too low	Check EEV operation; Inspect refrigerant volume; Check 4-port diverter valve
F.735	Evaporation temperature too high	Environment circuit temperature too high	Inspect system temperatures; Check refrigerant volume
F.737	Condensation temperature too high	Refrigerant circuit overfilled	Inspect refrigerant levels; Check system sensors and pressure switch
F.741	Building circuit: Return temp too low	Return temperature falls below 13°C during de-icing	Ensure minimum system volume; Activate backup heater if needed
F.752	Fault: Frequency converter	Internal electronics fault in inverter PCB	Check power supply cables; Verify inverter operation
F.753	Connection fault: Freq. converter	No communication between the frequency converter and control PCB	Inspect cable harness; Replace if needed
F.755	Fault: 4-port valve position incorrect	Incorrect 4-port diverter valve position	Inspect diverter valve coil and cable harness
F.774	Sensor fault: Air inlet temp	Sensor not connected or input short-circuited	Inspect and replace sensor; Replace cable harness
F.785	Fan unit 2: Fan blocked	No fan rotation detected	Check fan for blockages; Remove obstructions
F.788	Building circuit: Pump fault	High-efficiency pump detected fault	Switch off heat pump; Inspect pump operation
F.817	Freq. converter fault: Compressor	Compressor or frequency converter defect	Measure compressor winding resistance; Check cable harness and plug connections
F.818	Freq. converter fault: Mains voltage	Incorrect mains voltage for operating the frequency converter	Measure mains voltage; Correct voltage if needed
F.819	Freq. converter fault: Overheating	Internal overheating of frequency converter	Allow cooling; Check air flow and fan operation
F.820	Connection fault: Building circuit pump	Pump not sending a signal back to the heat pump	Check the cable; Replace the pump if needed
F.823	Hot gas temperature switch open	Hot gas thermostat shut down the heat pump due to high temperature	Check EEV; Replace dirt filter in the refrigerant circuit
F.825	Sensor fault: Capac. inlet temp.	Refrigerant circuit temperature sensor not connected or short-circuited	Check and replace the sensor if required
F.1117	Compressor: Phase failure	Defective fuse or incorrect electrical connections	Check fuse and electrical connections; Verify mains voltage
F.9998	Connection fault: Heat pump	eBUS cable not connected or connected incorrectly	Check eBUS cable connection between power supply PCB and control PCB

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How to Troubleshoot VaillantHeat Pump Faults

Here is a step-by-step guide for diagnosing and fixing your Vaillant heat pump:

Check the Display Panel: Look at the fault code displayed on the control screen.
Consult the Manual: Use the manual (available online if you can't find a copy) or our fault code table for reference.
Inspect the Unit: Check visible components such as wiring, sensors, and the pressure gauge.
Reset the Heat Pump: Turn off the unit, wait five minutes, and restart it.
Call a Professional: If the fault persists, contact a certified heating engineer.

Why Is My Vaillant Heat Pump Not Working?

An image of a Vaillant Arotherm Plus heat pump, with the front taken off so you can see the inner workings

Several factors can cause a Vaillant heat pump to stop working:

Low Water Pressure: If the pressure in your heating system is too low, the pump won’t operate correctly. Add water to the system until the pressure gauge is back within the recommended range, as per the installation manual.
Sensor Errors: Faulty temperature or pressure sensors can disrupt the heat pump’s performance.
Electrical Issues: Problems with power supply can shut down the unit; such as faulty wiring or a tripped breaker, .
Compressor Faults: A damaged compressor can cause major system failures and may need professional repair.

When to Call a Professional

While some Vaillant heat pump faults can be fixed at home, more complex issues require expert help. If your unit displays critical fault codes like F.819 (Frequency Converter Overheating) or F.823 (Hot Gas Temperature Switch Open), call a qualified heating engineer immediately.

Proactive Maintenance Tips for the Vaillant aroTherm Plus

Preventive maintenance can reduce system faults and extend your heat pump’s lifespan. Follow these tips:

Schedule an Annual Maintenance: Book an annual inspection with a certified technician. Contact us at hello@dwellow.co.uk if you don't have a service plan and would like to sign up for one.
Check for Debris: Ensure the outdoor unit is free from leaves, dirt and and other potential debris.
Inspect System Pressure: Regularly check the water pressure levels.
Monitor Performance: Try to keep an eye on heating efficiency and electricity usage of the unit.

Frequently Asked Questions(FAQs)

Q: How do I reset my Vaillant heat pump? A: Turn off the heat pump and then wait five minutes; and then restart the unit again. If the fault persists, contact a professional.

Q: What does F.022 mean on a Vaillant heat pump? A: It indicates low water pressure in the heating circuit. Top up the system and check for leaks.

Q: Why is my heat pump displaying F.731? A: This code points to a high-pressure switch fault.Inspect the pressure sensor and purge the system if necessary.

Q: Can I fix Vaillant fault codes myself? A: Some minor issues like topping up water pressure or resetting the unit can be fixed at home. However, complex faults like compressor failures should be handled by a technician.

Q: How can I prevent faultcodes on my Vaillant heat pump? A: Schedule regular maintenance, keep the unit clean, and inspect system pressure regularly.

Conclusion

By understanding the fault codes of the aroTherm Plus, you can troubleshoot common issues yourself, and then you can determine whether you need to call a professional. Use our comprehensive fault code table for quick reference and stay on top of your system’s maintenance to ensure year-round comfort.

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