Error D.13

Safety precautions:

- If you smell gas, leave the property immediately and call the gas emergency number; do not attempt any checks.

- Turn the boiler off at the main isolator before doing any hands-on work and don’t open the boiler casing or touch wiring unless you are a qualified engineer.

- If you see water leaking, close the cold water shut-off to the boiler/domestic cylinder and isolate the boiler power if safe to do so.

Initial homeowner checks you can safely do:

1) Check the boiler display for the exact code and any accompanying text; note if the code is D.13 versus F.13 and compare with your boiler manual because some models use different codes for pump vs sensor faults.

2) Try a simple reset of the boiler following the manufacturer’s reset procedure. If the code returns immediately or shortly after, proceed with the checks below.

3) Listen at the boiler when hot water is demanded: can you hear the pump running (a faint hum) or is it silent? If the pump runs but no hot water, that suggests an internal blockage or airlock; if the pump is silent it suggests no power or a failed pump.

4) Check that any external pump isolation valves (service valves) around the pump are open. The T-handle or slot should be aligned with the pipe to be open.

5) Check the electrical supply to the boiler and the fused spur (consumer unit) for a tripped breaker or blown fuse. Reset any tripped MCBs; if a fuse is blown, do NOT replace internal boiler fuses yourself — consult an engineer.

6) Check system water pressure on the boiler gauge; very low pressure can cause circulation and pump problems. If it is below the recommended range (usually around 1–1.5 bar) follow the manual to repressurise or call an engineer if you’re not confident.

7) Bleed nearby radiators to remove air locks in the heating circuit. If the hot water circuit includes radiators or a cylinder loop, trapped air can stop circulation.

Further diagnostic steps and fixes (professional required for many):

1) If external filters/strainers are fitted and accessible outside the boiler, isolate and clean them according to manufacturer guidance. Do not open the boiler casing to access internal strainers or pump housings.

2) If the pump does not run and external supply and fuses are okay, the pump motor may be seized or electrically faulty. This requires a Gas Safe engineer to test the pump, check wiring and replace the pump if necessary.

3) If the pump runs but flow is poor, the cause may be a blockage, faulty check valve, closed valve, or an airlock. A qualified engineer can isolate, strip and inspect the pump and pipework, remove debris, or power-flush the system if necessary.

4) If intermittent or unexplained behavior persists, the issue could be wiring to the pump, a relay or the boiler PCB. These electrical diagnostics and any PCB or wiring repairs must be carried out by an accredited engineer.

When to call a professional:

- If the D.13 error persists after a reset and the safe homeowner checks above.

- If you cannot safely access or check isolation valves, fuses or pressure.

- If there is any sign of leaks, seized pump, electrical faults, or you need internal access to the boiler.

Always call a Gas Safe registered engineer to diagnose and repair pump faults, replace the pump or perform electrical work. They have the correct parts, testing equipment and the required safety checks to restore the boiler and commission the repair safely.