E03 on a Trianco heat pump: Water Flow switch Protection
Short answer
On a Trianco heat pump, E03 means: Water Flow switch Protection. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the Activair High Temperature R290 (5/9/15/22kW)
The manual says: Water Flow switch Protection.
Part involved: water flow / water temperature.
Likely causes:
- Water pump failure.
- Water system not completely emptied of gas (air).
- Resistance of the water system too large.
- Valves of the water system not fully opened.
- Water circuit filter dirty and blocked.
- Water flow switch false connected or damaged.
On the Activair R410A indoor wall hung 3kW (S300)
The manual says: Water flow failure (no water or little water in water system).
Part involved: water flow / water temperature.
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.
What the engineer will check
On the Activair High Temperature R290 (5/9/15/22kW)
- Check flow switch and water pump per listed causes.
Who to ask for: heating / hydraulics.
Certification: Competent heating engineer (manufacturer training recommended).
On the Activair R410A indoor wall hung 3kW (S300)
- Check the flow volume, water pump is failure or not.
Who to ask for: heating / hydraulics.
Certification: Competent heating engineer (manufacturer training recommended).
What you might notice
Sources
- Trianco Activair High Temperature Air Source Heat Pump (R290 5/9/15/22kW) - Installation Operation and Service Manual ↗ · November 2024 (PDF regenerated 2026-08) · page 34 · Reviewed 23 September 2026
- Trianco Activair Wall Hung Air Source Heat Pump S300 (R410A indoor) - Installation Operation and Service Manual ↗ · 2023-07 · page 32 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026