Heat pumps · Error codes · Lämpöässä
soft-starterLämpöässä · Vsi / Vmi (ÄssäControl) GSHP with 430 l tank
soft-starter on a Lämpöässä Vsi / Vmi GSHP with 430 l tank: Soft starter AK1/AK4 fault signal
Short answer
On a Lämpöässä heat pump, soft-starter means: Soft starter AK1/AK4 fault signal. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Soft starter AK1/AK4 fault signal.
Likely causes:
- Soft starter AK1/AK4 fault signal.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
What you can check
- Note the code and any text shown on the display/controller.
- Check the heat pump isolator and consumer-unit breaker are on.
- Check the building main fuse / heat pump supply fuse (manual p.21).
What the engineer will check
- Check soft starter (alarms can be enabled in maintenance menu 5.4.11).
Who to ask for: heat pump engineer.
Sources
- LÄMPÖÄSSÄ Vmi 6-17 Ground Source Heat Pump - Instructions for use, installation and maintenance (7/2017) ↗ · 7/2017 · page 22 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026