Vaillant Heat pump F.774 error
ErrorF.774
F.774 is identified by Vaillant support as air-inlet temperature sensor fault. Follow the official, model-scoped checks and service boundary below.
✓
Reference source listed as Vaillant UK official heat-pump fault-code support.
Open official source ↗What the code means
air-inlet temperature sensor fault
Isolate the appliance when safe. Arrange Vaillant engineer service; do not test or replace the air sensor inside the heat-pump casing. Do not open fixed panels or test live circuits.
Typical symptoms
01F.774 appears on the heat pump display
02The affected heat pump function may stop, pause, or behave abnormally
03The code returns when the same model-specific condition is present again
Likely causes
Start with the least invasive explanation and stop if the check requires internal electrical or sealed-system access.
01air-inlet temperature sensor fault
02A model-specific condition must be confirmed against the exact manufacturer instructions
Safe next steps
- 1Record the complete F.774 display and the full Vaillant heat pump model
- 2Confirm that the displayed code matches the linked official Vaillant source
- 3Arrange Vaillant engineer service; do not test or replace the air sensor inside the heat-pump casing.
- 4Stop and arrange model-specific service if F.774 returns
Step-by-step repair
- 1Arrange Vaillant engineer service; do not test or replace the air sensor inside the heat-pump casing. No internal component replacement is verified from F.774 alone.
Repair details
€Estimated cost
The published checks normally need no replacement part. Internal repair cost is model- and region-specific; obtain a written Vaillant service quote after diagnosis.
The published checks normally need no replacement part. Internal repair cost is model- and region-specific; obtain a written Vaillant service quote after diagnosis.
⏱Estimated time
External checks take about 5–30 minutes; professional diagnosis and repair time depend on the exact model.
External checks take about 5–30 minutes; professional diagnosis and repair time depend on the exact model.
🔧Tools
Exact Vaillant model number and official manual, No internal electrical test tool is permitted
Exact Vaillant model number and official manual, No internal electrical test tool is permitted
▣Spare parts
No replacement part is confirmed by F.774 alone. Confirm the exact model, failed component, and manufacturer part number before ordering.
No replacement part is confirmed by F.774 alone. Confirm the exact model, failed component, and manufacturer part number before ordering.
What not to do
- Do not open fixed panels, test live electrical or sealed-system parts, bypass safety devices, or order a component solely from F.774.
Preventive maintenance
- 1Keep the washer level, use the detergent specified by the exact model manual, and keep accessible hoses, locks, and filters clear.
Frequently asked questions
What does F.774 mean?
Vaillant identifies it as air-inlet temperature sensor fault.
Can I replace a part from the code alone?
No. Confirm the exact model and manufacturer diagnosis first.
Did this fix your appliance?
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