E18 on a Toshiba heat pump: Regular communication failure between master and slave hydro unit (group control)
Short answer
On a Toshiba heat pump, E18 means: Regular communication failure between master and slave hydro unit (group control). The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 3 sources
What it means
On the R32 Estia 1-Series (split, Wall-Mounted and All-in-One)
The manual says: Regular communication failure between master and slave hydro unit (group control).
Part involved: interconnecting cable, remote controller, PCBs.
When it shows: Group communication lost.
Likely causes:
- Miswiring of master/slave hydro units.
On the Estia 5 Series (Standard)
The manual says: Regular communication error between master and slave hydro unit.
Part involved: interconnecting cable, remote controller, PCBs.
When it shows: Group communication lost.
Likely causes:
- Master/slave wiring.
On the Estia 5 Series Powerful (Hi Power / Extreme)
The manual says: Regular communication error between master and slave hydro unit.
Part involved: interconnecting cable, remote controller, PCBs.
When it shows: Trigger thresholds not printed in the IM; see SM.
Likely causes:
- Master/slave wiring.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: yes (per manual).
Manual reset: Clear the code from the remote controller once the cause is fixed (service procedure).
What you can check
- Note the check code shown on the remote controller and the outdoor/hydro model numbers before contacting an engineer.
- Check the consumer-unit breakers/isolators for the outdoor unit, hydro unit and backup heater are switched on.
What the engineer will check
On the R32 Estia 1-Series (split, Wall-Mounted and All-in-One)
- Follow manufacturer's check-code flowchart.
- Miswiring of master/slave hydro units.
Who to ask for: Heat pump engineer.
Certification: Electrical competence.
On the Estia 5 Series (Standard)
- Follow manufacturer's check-code flowchart.
- Master/slave wiring.
Who to ask for: Heat pump engineer.
Certification: Electrical competence.
On the Estia 5 Series Powerful (Hi Power / Extreme)
- Follow manufacturer's check-code flowchart.
- Master/slave wiring.
Who to ask for: Heat pump engineer.
Certification: Electrical competence.
What you might notice
Sources
- Air to Water Heat Pump Service Manual - Wall Mounted Type (File No. AE0-2101W) ↗ · AE0-2101W · page p.113 (printed page; PDF page +1) · Reviewed 23 September 2026
- Air to Water Heat Pump Service Manual (File No. A10-1704) - Estia 5 Series Indoor/Outdoor ↗ · A10-1704 · page p.88 (printed page; PDF page +1) · Reviewed 23 September 2026
- Hydro Unit Installation Manual EF99812301-4 (Powerful) ↗ · EF99812301-4 · page p.58 (printed page; PDF page +1) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026