S.516 on a Vaillant aroTHERM plus: De-icing mode active The heat pump de-ices the outdoor unit's heat exchanger. The heating mode is interrupted. The maximum de-icing time is 16 minutes
Short answer
On a Vaillant heat pump, S.516 means: De-icing mode active The heat pump de-ices the outdoor unit's heat exchanger. The heating mode is interrupted. The maximum de-icing time is 16 minutes. The heat pump keeps running.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: De-icing mode active The heat pump de-ices the outdoor unit's heat exchanger. The heating mode is interrupted. The maximum de-icing time is 16 minutes.
Part involved: Heat pump control (status/Live Monitor).
When it shows: De-icing mode active The heat pump de-ices the outdoor unit's heat exchanger. The heating mode is interrupted. The maximum de-icing time is 16 minutes.
Likely causes:
- Operating status reported by the heat pump control (not a fault in itself).
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Information only |
| Engineer needed? | No |
The heat pump keeps running.
Resetting itself: yes - status changes automatically with operating state.
Manual reset: not applicable.
What you can check
- Normal defrost: the outdoor unit may give off a cloud of vapour and heating pauses briefly - no action needed. Keep the outdoor unit clear of snow/ice build-up.
What the engineer will check
- None required unless heating/hot water is not delivered; then review status history, settings and application limits.
Who to ask for: Vaillant-trained heat pump installer/engineer (MCS-certified installer).
Certification: MCS installer certification; Vaillant product training recommended.
What you might notice
What owners and engineers report
5 owner and engineer reports mention this.
- Frequent defrosting on the aroTHERM plus (VWL ../6 A): 5 reports
Sources
- Heat pump control interface module (VWZ AI) operating and installation instructions ↗ · 0020291573_01 · page VWZ AI appliance interface 0020291573_01 p.33; uniTOWER VIH QW 190/6 E 0020291525_05 p.58; VWZ MEH 97/6 hydraulic station 0020291544_03 p.51; aroTHERM split hydraulic station VWL ../5 IS 0020257319_05 p.56 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026