H06.17 on a Baxi HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP: DeltaT CH max limit The Delta Temperature on the central heating side exceeds the maximum overshoot
Short answer
On a Baxi heat pump, H06.17 means: DeltaT CH max limit The Delta Temperature on the central heating side exceeds the maximum overshoot. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: DeltaT CH max limit The Delta Temperature on the central heating side exceeds the maximum overshoot.
Part involved: water flow / pressure.
Likely causes:
- Check whether the water filter needs cleaning. Make sure that there is no air in the system (venting). Check the water pressure. The water pressure must be above 1 bar (0.1 MPa) (at low temperature). Check that the pump's speed setting is the highest speed. Make sure that the expansion vessel is not broken. Check that the resistance in the hydraulic circuit is not too high for the pump.
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
- Check whether the water filter needs cleaning. Make sure that there is no air in the system (venting). Check the water pressure. The water pressure must be above 1 bar (0.1 MPa) (at low temperature). Check that the pump's speed setting is the highest speed. Make sure that the expansion vessel is not broken. Check that the resistance in the hydraulic circuit is not too high for the pump.
Who to ask for: heating / heat pump engineer (hydraulics).
Certification: None beyond heating competence (MCS installer recommended).
What you might notice
Sources
- 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