high-pressure-error on a Danfoss heat pump: High pressure switch has deployed
Short answer
On a Danfoss heat pump, high-pressure-error means: High pressure switch has deployed. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the DHP-AQ
The manual says: High pressure switch has deployed.
Part involved: high pressure switch.
Likely causes:
- Air in heating system; blocked strainer; closed thermostats/valves; defective/jammed circulation pump; closed main tap; cable break to HP switch; wrong/faulty HP switch; timer shunt closing circuit; non-return valve wrong way or too stiff; large pressure drop; blocked condenser (water or refrigerant side); overfilled refrigerant circuit.
On the DHP-H
The manual says: Tripped high pressure switch. Compressor stopped.
Part involved: high pressure switch.
Likely causes:
- Blocked strainer in heating system; air in heating system; closed/partly closed thermostats or valves; defective or jammed circulation pump; closed main tap in heating system; broken/loose cable to HP switch; faulty or wrong HP switch; timer-controlled shunt closing heating circuit; wrong-way or high-opening-pressure non-return valve; large pressure drop in heating system; overfilled refrigerant circuit; condenser blocked (water or refrigerant side).
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Manual reset: Set operating mode OFF then back to the desired mode.
What you can check
On the DHP-AQ
- Note the exact alarm text. 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. The manual allows acknowledging by setting operating mode OFF then back once; if the alarm returns, call an engineer.
On the DHP-H
- 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
On the DHP-AQ
- Bleed heating system; clean strainer; check pump voltage and 0-10 V signal; check HP switch and cabling; check non-return valve; condenser dT test (<3 K or >13 K suggests blockage); check charge.
Who to ask for: heat pump engineer.
Certification: F-Gas category I certificate (refrigerant circuit work).
On the DHP-H
- Clean heating strainer; bleed heating system; verify circulation pump voltage/rotation via manual test menu; check HP switch cabling and break pressure (R407C HP switch 3.10 MPa, R404A 3.10 MPa) with gauges; check non-return valve orientation; check superheat/charge; test condenser dT (<3 K or >13 K suggests blockage).
Who to ask for: heat pump engineer.
Certification: F-Gas category I certificate (refrigerant circuit work).
What you might notice
Sources
- Service Instructions DHP-AQ (VMGFJ202) ↗ · VMGFJ202 · page p.10; pp.16-17 · Reviewed 23 September 2026
- 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 (alarm table), pp.39-41 (Table 14); PDF pp.37, 41-43 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026