Heat pumps · Error codes · Vaillant
M.49Vaillant · flexoTHERM exclusive (VWF ../4)
M.49 on a Vaillant flexoTHERM exclusive: Environment circuit: Brine lines inverted
Short answer
On a Vaillant heat pump, M.49 means: Environment circuit: Brine lines inverted. The heat pump keeps running. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Environment circuit: Brine lines inverted.
Part involved: Brine lines inverted.
Likely causes:
- Brine lines to the air-to-brine collector connected the wrong way round (only with heat source: air).
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running.
Resetting itself: clears when condition resolved.
Manual reset: engineer resets maintenance message.
What you can check
- Note the full code and text shown on the display (and the date/time it appeared). Contact your installer or Vaillant Service; do not attempt any repair.
What the engineer will check
- Check that the connections are correctly assigned to the brine lines.
Who to ask for: Vaillant-trained heat pump installer/engineer (MCS-certified installer).
Certification: MCS ground-source installer; F-gas certificate for refrigerant work.
What you might notice
Sources
- flexoTHERM exclusive VWF 57/4 - 197/4 400V installation and maintenance instructions ↗ · 0020213394_05 · page flexoTHERM 400 V 0020213394_05 p.50; flexoTHERM 230 V 0020213395_04 p.45 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026