Error D.10

Safety precautions:

- If you are unsure or uncomfortable at any point, stop and call a Gas Safe registered engineer. Do not attempt internal repairs on a gas appliance.

- Before any visual checks, turn the boiler off at the main switch. Do not remove covers or access live terminals with power connected unless you are a qualified electrician/engineer.

- Do not repeatedly reset the boiler. Repeated resets can mask a persistent fault and cause further damage.

Initial checks a homeowner can do (no special tools required):

1. Check boiler display and error history: note the D.10 occurrences (steady, intermittent, after calling for heat). Take a photo of the display for the engineer if needed.

2. Check system water pressure on the boiler gauge. Typical cold pressure is around 1.0–1.5 bar. If it is significantly low (below ~0.8–1.0 bar), top up using the filling loop per the manual, then check if the error clears after the boiler reinitialises.

3. Listen for the pump when the boiler is calling for heating: you should hear a low humming when the pump runs. If you hear nothing at all it suggests the pump is not running.

4. Bleed radiators to remove airlocks. Air trapped in the system can prevent proper circulation and mimic a pump fault.

5. Ensure any external isolation valves in the pipework to/from the boiler or pump are fully open (only if these are clearly labelled and accessible).

6. Reset once: switch the boiler off, wait 30 seconds, switch back on and use the reset function once. If the D.10 returns immediately or shortly after, further investigation is required.

Specific diagnostic and safe checks (for competent DIYers only; power isolated):

1. With the boiler powered off at the isolator and confirmed off, visually inspect accessible pump area and wiring for obvious loose connectors, burnt wiring or signs of water ingress. Do not open or tamper with sealed components.

2. If you are comfortable and competent with basic electrical isolation and continuity checks, you may note down connector positions for the engineer, but do not attempt to measure live circuits or replace the pump yourself unless you are qualified and Gas Safe registered.

3. If you can access the installer/diagnostic menu without changing settings, you can view diagnostic values (flow rate, pump status, etc.) and log those readouts for the engineer. Do not alter installer settings.

When to call a professional and what they will do:

- Call a Gas Safe registered heating engineer if the D.10 persists after the basic checks, if you find no pump noise when heating is called, if the pump appears seized, or if you find electrical/wiring concerns. The engineer will safely isolate, open the boiler, test pump electrical supply and motor current, check pump impeller for seizure, test and replace the pump if necessary, verify wiring and terminal connections, check system pressure sensors and NTC sensors, and inspect the PCB if the pump is powered but the boiler does not detect it. They can also power-flush or clear blockages and remove airlocks if required.

Additional notes:

- Do not attempt to replace the internal pump or access internal gas-containing parts unless you are a Gas Safe engineer. Work on gas appliances and live electrical components is dangerous and illegal for unqualified persons.

- Keep a record of the fault code occurrences, any actions you took, and photos of the boiler display and pressure gauge to help the engineer diagnose more quickly.