Heat pumps · Error codes · Firebird
73Firebird · Enviroair (Hitachi Yutaki M based) 7.5-16kW monobloc
73 on a Firebird Enviroair 7.5-16kW monobloc: Mixing over-temperature limit protection for mixed circuit
Short answer
On a Firebird heat pump, 73 means: Mixing over-temperature limit protection for mixed circuit. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Mixing over-temperature limit protection for mixed circuit.
Part involved: water flow / water temperature.
Likely causes:
- Circuit 2 supply temperature > target temperature + offset.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
What you can check
- Note the exact code shown on the controller (a photo helps) and report it to your installer or the manufacturer's service line.
- Check the heat pump's supply breaker/isolator at the consumer unit is on (do not open any casing).
- Check the heating system pressure gauge reading (if one is fitted) and tell your engineer if it is below the level set at commissioning; do not attempt to refill unless you have been shown how.
- If the controller shows red/alarm, the Firebird Enviroair Hitachi end-user guide allows a reset by pressing the ON button for 3 seconds and again; if it goes red again, contact your engineer.
What the engineer will check
- Check: Circuit 2 supply temperature > target temperature + offset.
Who to ask for: heating / hydraulics.
Certification: Competent heating engineer (manufacturer training recommended).
What you might notice
Sources
- Firebird Enviroair Air Source Heat Pumps - Installation & Operation Manual (Enviroair 7.5/11/14/16kW, R410A monobloc) ↗ · Dec 2017 · page 52 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026