Vaillant · Heat pump

Vaillant Heat pump F.1120 error

ErrorF.1120

F.1120 is identified by Vaillant support as immersion-heater phase failure. 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 ↗

Stop and make safe

immersion-heater phase failure

Isolate the appliance when safe. Contact a qualified heating installer or Vaillant engineer for supply, phase, wiring, and immersion-heater diagnosis; do not test live circuits. Do not open fixed panels or test live circuits.

Typical symptoms

01F.1120 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.

01immersion-heater phase failure

02A model-specific condition must be confirmed against the exact manufacturer instructions

Safe next steps

1
Record the complete F.1120 display and the full Vaillant heat pump model
2
Confirm that the displayed code matches the linked official Vaillant source
3
Contact a qualified heating installer or Vaillant engineer for supply, phase, wiring, and immersion-heater diagnosis; do not test live circuits.
4
Stop and arrange model-specific service if F.1120 returns

Step-by-step repair

1
Contact a qualified heating installer or Vaillant engineer for supply, phase, wiring, and immersion-heater diagnosis; do not test live circuits. No internal component replacement is verified from F.1120 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.

⏱Estimated time
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

▣Spare parts
No replacement part is confirmed by F.1120 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.1120.

Preventive maintenance

1
Keep 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.1120 mean?

Vaillant identifies it as immersion-heater phase failure.

Can I replace a part from the code alone?

No. Confirm the exact model and manufacturer diagnosis first.

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