S.276 on a Vaillant heat pump: Building circuit: Lockout contact S20 open Contact S20 is open at the heat pump's main PCB. Incorrect limit thermostat setting. Flow temperature sensor (heat pump, gas-fired boiler, system sensor) measures values that deviate downwards. Adjust the maximum flow temperature for the direct heating circuit via …
Short answer
On a Vaillant heat pump, S.276 means: Building circuit: Lockout contact S20 open Contact S20 is open at the heat pump's main PCB. Incorrect limit thermostat setting. Flow temperature sensor (heat pump, gas-fired boiler, system sensor) measures values that deviate downwards. Adjust the maximum flow temperature for the direct heating circuit via …. The heat pump keeps running with some functions stopped. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 3 sources
What it means
On the aroTHERM plus (VWL ../6 A)
The manual says: Building circuit: Lockout contact S20 open Contact S20 is open at the heat pump's main PCB. Incorrect limit thermostat setting. Flow temperature sensor (heat pump, gas-fired boiler, system sensor) measures values that deviate downwards. Adjust the maximum flow temperature for the direct heating circuit via ….
Part involved: Heat pump control (status/Live Monitor).
When it shows: Building circuit: Lockout contact S20 open Contact S20 is open at the heat pump's main PCB. Incorrect limit thermostat setting. Flow temperature sensor (heat pump, gas-fired boiler, system sensor) measures values that deviate downwards. Adjust the maximum flow temperature for the direct heating circuit via ….
Likely causes:
- Operating status reported by the heat pump control (not a fault in itself).
On the flexoTHERM exclusive (VWF ../4)
The manual says: Building circuit: Lockout contact S20 open.
Part involved: Heat pump control (status/Live Monitor).
When it shows: See official description.
Likely causes:
- Operating status reported by the heat pump control (not a fault in itself).
On the geoTHERM mini (VWS 30/4, VWS 36/4.1)
The manual says: Building cir.: Lockout contact S20 opened.
Part involved: Heat pump control (status/Live Monitor).
When it shows: See official description.
Likely causes:
- Operating status reported by the heat pump control (not a fault in itself).
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Information only |
| Engineer needed? | No |
The heat pump keeps running with some functions stopped.
Resetting itself: yes - status changes automatically with operating state.
Manual reset: not applicable.
What you can check
- Operating status only - no action needed. If heating or hot water is not being delivered for a long period, note the status code and tell your installer.
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.
Sources
- Heat pump control interface module (VWZ AI) operating and installation instructions ↗ · 0020291573_01 · page VWZ AI appliance interface 0020291573_01 p.32; uniTOWER VIH QW 190/6 E 0020291525_05 p.57; VWZ MEH 97/6 hydraulic station 0020291544_03 p.50; aroTHERM split hydraulic station VWL ../5 IS 0020257319_05 p.55 · Reviewed 23 September 2026
- flexoTHERM exclusive VWF 57/4 - 197/4 400V installation and maintenance instructions ↗ · 0020213394_05 · page flexoTHERM 400 V 0020213394_05 p.49; flexoTHERM 230 V 0020213395_04 p.44 · Reviewed 23 September 2026
- geoTHERM mini VWS 36/4.1 230 V installation manual ↗ · 0020250181_00 · page geoTHERM mini 0020250181_00 p.36 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026