Overview
D.13 on a Vaillant EcoTEC Plus regular is a diagnostic code that points to a problem with the hot water circulation (cylinder charging) pump or its associated circuitry. In plain terms it means the boiler has detected that the pump responsible for moving heated water to the domestic hot water cylinder (or keeping the cylinder topped up for “warm start”) is not behaving as expected — not running, running too slowly, electrically disconnected, or blocked. This fault usually causes loss of hot water or prevents the boiler from charging the cylinder properly. Severity is moderate: it does not normally present an immediate gas safety danger, but it will stop hot water and can cause the boiler to go into safety shutdowns if temperatures or pressures move outside safe ranges. Because the pump and wiring work with mains voltage and the boiler has internal components that should only be accessed by trained personnel, most corrective actions require a Gas Safe registered engineer. Homeowners can perform preliminary, non-invasive checks (reset, visual checks, check pressure) but should not attempt internal repairs, wiring or pump replacement themselves.
Possible Cause: Hot water circulation pump
Troubleshooting Steps
Safety precautions:
- Do not open the boiler casing or attempt to work on internal electrical components unless you are a qualified Gas Safe engineer. Internal work risks electric shock and gas hazards.
- Before doing any external checks, isolate the boiler electrically at the boiler isolator or fuse spur and confirm the power is off.
- If you suspect a water leak, switch off and isolate the system and call a professional.
Initial quick checks a homeowner can do (non-invasive):
1. Note any other error codes or messages on the display and the exact conditions when D.13 appeared (e.g. after a hot tap was opened, after running for some time, after a power cut).
2. Try a simple reset: clear the fault with the boiler reset button or follow the boiler handbook reset sequence. If the code returns immediately or shortly after, further checks are needed.
3. Check boiler pressure on the gauge (cold pressure should normally be around 1.0–1.5 bar on most systems). If pressure is very low, top up the system per the boiler handbook and then see if the fault clears.
4. Listen at the boiler and cylinder area for pump noise when a hot tap is opened or during a hot-water call. If you hear the pump running (a steady hum) the pump may be trying to operate; if it is silent and you expect it to run, that indicates a likely pump or supply fault.
5. If your system uses a separate external cylinder pump: confirm the pump’s isolator switch (if fitted) is ON and any external fuses or RCDs have not tripped.
Further diagnostic steps (call an engineer if you are unsure):
1. If the pump is external and you are competent with basic electrical isolation: turn off power to the boiler and pump, ensure isolator is off, then visually check the pump and pipework for obvious signs of seizure, corrosion, or leaks. Do not open the pump casing or touch wiring unless qualified.
2. Check that inlet/outlet valves to the cylinder and pump are open (some installations have isolation valves). A closed valve can prevent circulation and trigger the error.
3. If the pump has a removable strainer or filter in front of it (some installations do), an engineer can check and clean that filter if blocked with debris — do not try to remove internal strainers inside the boiler yourself.
4. Airlock/blocked impeller: symptoms include a noisy pump, poor flow, or pump running without producing hot water. An engineer can purge airlocks or free a jammed impeller safely.
5. Electrical and sensor checks: a qualified engineer will confirm the pump is receiving the correct mains voltage, check motor current/amp draw, test the pump motor and wiring, and verify any temperature or flow sensors associated with the hot water circuit. They will also check the boiler PCB for stored diagnostic data related to D.13.
When to call a professional and what they will do:
- Call a Gas Safe registered heating engineer if resetting does not clear the fault, the pump does not run when it should, you hear grinding/strange noises from the pump, you find closed isolation valves you cannot safely operate, or there are leaks or multiple fault codes.
- A qualified engineer will isolate and test electrical supply to the pump, test/replace the pump if seized or failed, check and clear blockages or airlocks, inspect associated sensors and wiring, and verify safe operation of the boiler after repair.
Important notes:
- Do not repeatedly reset the boiler to clear the code without addressing the underlying fault — repeated resets can cause more damage.
- Working inside the boiler or on gas/pressurised water circuits must only be done by a qualified engineer. If D.13 is present and initial homeowner checks haven’t fixed it, book a Gas Safe engineer and report the D.13 code and any observations (noises, pressure readings, when it happens) to help diagnosis.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Vaillant EcoTEC Plus Regular Gas Boiler.