Heat pumps · Error codes · Navien
TPNavien · PEM750
TP on a Navien PEM750: Low ambient temp. protection
Short answer
On a Navien heat pump, TP means: Low ambient temp. protection. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 24 September 2026 · 1 source
What it means
The manual says: Low ambient temp. protection.
Part involved: see manual.
Likely causes:
- Ambient <=-30 C; clears when ambient is -28 C or higher.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: yes.
What you can check
- Note the code shown on the controller and the model number on the unit's rating label before contacting your installer.
- Check that the heat pump's isolator and consumer-unit breaker are on; do not open any casing.
- This is a protection for extremely low outdoor temperature (-30 C or below) and clears automatically when it warms up.
What the engineer will check
- Follow the manufacturer's troubleshooting for this code.
Who to ask for: Heat pump engineer.
Certification: Heat pump installer competence; F-gas and flammable-refrigerant (R32/R290) handling competence for any refrigerant-circuit work.
What you might notice
Sources
- Navien Air to Water Heat Pump UK Service Manual (EN, 250408) ↗ · 250408 · page printed p.72 (PDF p.73) · Reviewed 24 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 24 September 2026