347 on a Mitsubishi Heavy Industries Air-Conditioning Europe Hydrolution: Temp high press: Temporary high pressure alarm
Short answer
On a Mitsubishi Heavy Industries Air-Conditioning Europe heat pump, 347 means: Temp high press: Temporary high pressure alarm. 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: Temp high press: Temporary high pressure alarm.
Part involved: Temp high press.
When it shows: Temporary high pressure alarm.
Likely causes:
- No/low water flow; air in water system.
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.
Resetting itself: no.
Manual reset: yes.
What you can check
- Note the alarm number/text shown on the display. Check the consumer-unit breakers/isolators for the indoor and outdoor units are on. Check radiator/underfloor thermostats in the house are not all closed (user manual). Check the heating system pressure gauge reads in the normal range (about 0.5-1.5 bar when cold for Hydrolution per user manual). Select 'reset alarm' once; if it returns contact the installer.
What the engineer will check
- Check water flow, air in system, pump; refrigerant-side checks by F-gas engineer.
Who to ask for: Heat pump / refrigeration engineer (manufacturer-trained).
Certification: F-gas certification for refrigerant-circuit work; electrical competence (Part P/18th Edition) for PCB/wiring.
What you might notice
Sources
- Installation Manual - Air to Water Heat Pump Hydrolution (HM) ↗ · PSC012D085CD · page PDF p.89 (printed 87) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026