H1 on a LG THERMA V Water Heater: Water temperature is too high (THERMA V water heater)
Short answer
On a LG heat pump, H1 means: Water temperature is too high (THERMA V water heater). 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 temperature is too high (THERMA V water heater).
Part involved: high-limit safety / water temperature control.
When it shows: Water temperature is too high.
Likely causes:
- Water temperature is too high.
Is it safe?
Switch the heat pump off at its isolator and call an engineer.
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Safety lockout |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: unknown.
Manual reset: Per LG corrective action; service engineer for most codes.
What you can check
- Note the code shown on the water heater display. LG's corrective action: call LG technical support. While the fault is present the unit operates as: OFF – no hot water from this unit.
What the engineer will check
- Find overheat cause (control relay welded, sensor fault), check and reset ECO per LG procedure, verify T&P valve.
Who to ask for: Heat pump engineer / electrician (inverter and PCB diagnostics).
Certification: Competent person for electrical work (BS 7671); isolate and wait 3 min for DC-link discharge.
What you might notice
Sources
- LG Heat Pump Water Heater Owner's Manual WH20S F5 / WH27S F5 (EU/UK multilingual), MFL71409209 Rev.00 (2023) – ManualsLib 3195149 ↗ · MFL71409209 Rev.00_090823 · page 32 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026