Heat pumps · Error codes · Navien
E19Navien · PEM750
E19 on a Navien PEM750: Primary antifreeze protection
Short answer
On a Navien heat pump, E19 means: Primary antifreeze protection. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 24 September 2026 · 1 source
What it means
The manual says: Primary antifreeze protection.
Part involved: water circuit frost protection.
Likely causes:
- Winter protection (ambient <=0 C and low inlet water); clears when water rises (A04+4 C / 8 C) or ambient >1 C.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
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.
- Check the outdoor unit is not blocked by snow, ice, leaves or debris, and do not clear ice from the fins with tools.
What the engineer will check
- Check water flow and outlet water temperature sensor.
- Check antifreeze heaters and defrost operation.
- Check system water volume.
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.69 (PDF p.70) · Reviewed 24 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 24 September 2026