Heat pumps · Error codes · Danfoss
03Danfoss · DHP-AT
03 on a Danfoss DHP-AT: Water flow switch protection
Short answer
On a Danfoss heat pump, 03 means: Water flow switch protection. 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: Water flow switch protection.
Part involved: Water flow switch protection.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
What you can check
- Note the 2-digit code. Check the heating-system pressure gauge is in the range given in the user guide (Thermia/Danfoss: 1-1.5 bar when cold) - do not top up yourself unless you have been shown how; check radiator/underfloor valves and room thermostats are open. If the code persists, call an engineer.
What the engineer will check
- Flow switch blocks operation below permitted flow and self-resets when flow returns (p.16): check pump, strainer, valves, air, flow switch.
Who to ask for: heat pump engineer.
What you might notice
Sources
- Installation Guide DHP-AT - Installation and service manual (VMGFI302 / AN089486453198) ↗ · VMGFI302 · page p.32 (section 10.1.1); safety functions pp.16-17 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026