Heat pumps · Error codes · Danfoss
aux-heaterDanfoss · DHP-H
aux-heater on a Danfoss DHP-H: Overheating protection deployed. No auxiliary heater
Short answer
On a Danfoss heat pump, aux-heater means: Overheating protection deployed. No auxiliary heater. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Overheating protection deployed. No auxiliary heater.
Part involved: immersion/electric heater overheat protection.
Likely causes:
- Overheat protection tripped; phase drop (230 V not registered between L2 and N); faulty overheat protection that cannot be reset; flow sensor fault; no/insufficient circulation in heating system; immersion tube touching coils (trips ~95°C).
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Manual reset: Set operating mode OFF then back to the desired mode.
What you can check
- Note the exact alarm text. The manual allows acknowledging by setting the operating mode to OFF and then back to the previous mode - do this once; if the alarm returns, leave it and call an engineer. 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.
What the engineer will check
- Reset overheat protector (button on electrical panel); check 230 V in/out of protector; check flow sensor resistance; check circulation pump, valves, strainer and air; reposition immersion tube.
Who to ask for: heat pump engineer.
Certification: Qualified electrician / heat pump engineer (electrical fault-finding).
What you might notice
Sources
- Service instructions DHP-A, DHP-A Opti, DHP-AL, DHP-AL Opti, DHP-C, DHP-H, DHP-H Opti, DHP-H Opti Pro, DHP-L, DHP-L Opti, DHP-L Opti Pro (VMGFC302) ↗ · VMGFC302 (© 2010; PDF regenerated 2024-07-10 on assets.danfoss.com) · page printed p.35, p.43 (Table 18); PDF pp.37, 45 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026