Error D.72

Safety precautions:

- If you are unsure at any point, switch the boiler off at the isolator and the mains and call a Gas Safe engineer.

- Do not open or remove covers from the boiler while it is live or connected to gas. Internal work must only be done by a qualified engineer.

- If you smell gas, leave the property immediately, call the gas emergency number and do not operate electrical switches or the boiler.

Initial homeowner checks you can safely do:

1) Note the exact fault code, when it occurred and any other codes displayed. This information is useful for an engineer.

2) Reset the boiler once using the reset button. If the D.72 clears and does not return, monitor the boiler for repeat occurrence. Avoid repeated resets multiple times in a short period.

3) Check the system pressure on the boiler gauge. Ensure pressure is in the normal range (typically ~1.0–1.5 bar for most domestic systems). Top up using the filling loop only if pressure is low and you are comfortable doing so.

4) Bleed a couple of radiators to remove trapped air and then re-check the pump behaviour and boiler operation.

5) Listen at the boiler: after shutdown does the pump run for a short time? Note any unusual noises (grinding, loud humming) or lack of pump noise which could indicate a seized pump.

6) Ensure any isolation valves to the pump or system pipework beneath the boiler are fully open.

Specific diagnostic and basic fix steps (homeowner-level):

1) Reset and observe: press reset once and watch the boiler through a full demand cycle (call for hot water or heating). Note whether D.72 reappears and under what conditions (after DHW, after CH start, only on warm start, etc.).

2) Confirm circulation: run the heating and feel radiators. If the radiators remain cold or only the first radiator warms, there may be circulation issues or airlocks — bleed radiators and re-check.

3) Pump audible check: with the boiler on, stand near the boiler and listen. A working pump usually produces a soft hum. A loud noise, clunking or silence can indicate a failing or seized pump.

4) Check for blockages/airlocks in visible pipework and radiator TRVs. If you suspect an airlock you can try repeatedly venting radiators or, for installers, slightly opening the system drain points — but do not attempt invasive operations on the boiler itself.

5) If the fault refers to temperature difference or sensors (D.72 is sometimes linked to flow/return difference), document if the boiler displays unusually high flow temperatures or if the boiler is overheating. If the boiler has an overheating warning, switch it off and allow it to cool, then call an engineer.

When to call a professional (and what they will check):

- Call a Gas Safe qualified heating engineer if D.72 persists after your initial checks, returns frequently, appears with other fault codes, or if you detect pump noise problems, loss of heating/hot water, overheating or unusual smells.

- The engineer will isolate the boiler and carry out safe internal diagnostics: check pump operation and speed settings, confirm pump impeller is not seized, check and test flow and return NTC sensors and their wiring, inspect PCB fault logs, verify isolation valves and hydraulic components, and check for blockages, debris or scale in the heat exchanger and system (power flush may be recommended if debris is present).

- If sensors, the pump, wiring harness or PCB are faulty these components should only be replaced by a qualified engineer. The engineer will also ensure the appliance is leak-free and safe to return to service.

Final notes:

- Do not attempt to repair or replace the pump, sensors, wiring or any gas components yourself. These are live electrical and gas-containing parts that require certified competence.

- Keep a record of when the fault occurs and any actions you have taken to help the engineer diagnose the problem quickly. If the fault is intermittent, give as much detail as possible about operating conditions when it appears (hot water use, central heating call, warm start behavior).