H02.23 on a Baxi heat pump: System flow error System water flow error active
Short answer
On a Baxi heat pump, H02.23 means: System flow error System water flow error active. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 2 sources
What it means
On the Assure Split ASHP (AWHP 4.5/6/8 MR + Assure AWHP-IDU 4-8 E)
The manual says: System flow error System water flow error active.
Part involved: water flow / pressure.
Likely causes:
- Flow problem Insufficient flow: open a radiator valve. The circuit is clogged: Check that the filters are not obstructed and clean them if necessary. Clean and flush the installation, No circulation: Check that the valves and thermostatic valves are open, Check that the circulating pump is working, Check the wiring, Check the pump supply: if the pump does not work, replace it. Too much air: completely vent the indoor unit and the installation for optimum running. Incorrect wiring: check the electrical connections. Flow meter: Check the electrical connections and the direction of the flow meter (arrow to the right). Replace the flow meter if necessary.
On the HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP (R290)
The manual says: System flow error System water flow error active.
Part involved: water flow / pressure.
Likely causes:
- Flow problem Insufficient flow: open a radiator valve. The circuit is clogged: Check that the filters are not obstructed and clean them if necessary. Clean and flush the installation. No circulation: Check that the valves and thermostatic valves are open, Check that the circulating pump is working, Check the wiring, Check the pump supply: if the pump does not work, replace it. Too much air: completely vent the indoor unit and the installation for optimum running. Incorrect wiring: check the electrical connections. Flow rate sensor: Check the electrical connections and the direction of the flow meter (arrow to the right). Replace the flow meter if necessary.
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 - system restarts automatically when the cause disappears (may run in degraded/back-up mode meanwhile).
Manual reset: not required once cause removed.
What you can check
- Note the exact code shown on the controller and when it appeared.
- Read the heating system pressure gauge and report the value to your installer (the manuals quote a minimum of about 1 bar cold).
- Check the filling loop is closed.
- In freezing weather do not leave the system switched off - the manuals warn water faults left unrepaired in winter can let the pump and pipes freeze.
- The manual's user steps allow switching the system off and on once to see if the error clears; if the code returns, contact the installer.
- If the code persists or returns, contact a heat pump engineer.
What the engineer will check
On the Assure Split ASHP (AWHP 4.5/6/8 MR + Assure AWHP-IDU 4-8 E)
- Flow problem Insufficient flow: open a radiator valve. The circuit is clogged: Check that the filters are not obstructed and clean them if necessary. Clean and flush the installation, No circulation: Check that the valves and thermostatic valves are open, Check that the circulating pump is working, Check the wiring, Check the pump supply: if the pump does not work, replace it. Too much air: completely vent the indoor unit and the installation for optimum running. Incorrect wiring: check the electrical connections. Flow meter: Check the electrical connections and the direction of the flow meter (arrow to the right). Replace the flow meter if necessary.
Who to ask for: heating / heat pump engineer (hydraulics).
Certification: None beyond heating competence (MCS installer recommended).
On the HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP (R290)
- Flow problem Insufficient flow: open a radiator valve. The circuit is clogged: Check that the filters are not obstructed and clean them if necessary. Clean and flush the installation. No circulation: Check that the valves and thermostatic valves are open, Check that the circulating pump is working, Check the wiring, Check the pump supply: if the pump does not work, replace it. Too much air: completely vent the indoor unit and the installation for optimum running. Incorrect wiring: check the electrical connections. Flow rate sensor: Check the electrical connections and the direction of the flow meter (arrow to the right). Replace the flow meter if necessary.
Who to ask for: heating / heat pump engineer (hydraulics).
Certification: None beyond heating competence (MCS installer recommended).
What you might notice
Sources
- Installation and Service Manual - Air/water 'Split Inverter' heat pump Baxi Assure, Assure AWHP-IDU 4-8 E ↗ · 7762758 - v05 - 19082020 · page 91 · Reviewed 23 September 2026
- Installation, user and service manual - Indoor unit ASHP Control ↗ · 7887625 - v04 - 22072025 · page 128 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026