Error 265

Safety precautions:

- Do not open the boiler casing or attempt gas-side repairs unless you are a qualified Gas Safe engineer. Working on gas appliances is dangerous and illegal for unqualified persons.

- Turn off the boiler mains switch before doing any non-visual checks and do not tamper with internal electronics or gas components.

- If you smell gas, evacuate the property, close the gas supply at the meter if safe to do so, and call the gas emergency number immediately.

Initial homeowner checks you can safely do:

1) Note timings and behaviour: when the boiler cycles to partial load, how long it runs, and whether it coincides with a room thermostat or hot water demand. Write down any additional fault codes or LEDs shown on the display.

2) Check room thermostat and programmer: make sure the thermostat setpoint and schedule are correct, batteries in wireless stats are OK, and there are no rapid on/off calls for heat.

3) Check radiator valves and zones: ensure thermostatic radiator valves (TRVs) and zone valves are open on a circuit calling for heat. If many TRVs are closed the boiler may be oversized for the actual load.

4) Check system pressure: look at the pressure gauge on the boiler. If pressure is low (typically below about 1.0 bar for GB162 commercial guidance or less than 0.8–1.0 bar for domestic systems) repressurise as per your manual. Do not overpressurise.

5) Bleed radiators: air in the system can cause short cycling or uneven heating. Bleed radiators and top up pressure if needed.

6) Check pump operation: listen for the heating pump running when there is a heat demand. A failed pump or very low pump speed can cause rapid temperature rise at the flow sensor and modulation behaviour.

7) Check boiler mode: ensure the boiler is not in manual/test or sweep mode and that it is set to normal heating operation. Avoid repeatedly pressing reset unless told to by an engineer.

Specific diagnostic steps and possible fixes (safe for homeowners up to the point of intervention):

1) Access the info menu and record the operating cause code and any other codes. Error 265 is an operating-state code; note if other error codes are present (e.g., 260, CE 207, E2/E9 codes) because those point to sensor or pressure problems.

2) If the boiler is regularly going to partial load within a few minutes of starting, try temporarily increasing the CH flow set temperature slightly (if you are comfortable changing settings) and observe whether the boiler runs longer before dropping back. If this makes a noticeable improvement you may be able to reduce short cycling, but keep temperatures reasonable for your system.

3) Temporarily disable or raise the room thermostat setpoint briefly to test whether the thermostat is causing rapid on/off cycling. If the boiler then runs normally, the thermostat or its wiring may be at fault.

4) Put the boiler into manual heating mode (per the GB162 manual) so it remains calling for heat and observe behavior. If it runs steadily in manual mode, that indicates an upstream control (thermostat/zone controller) or sensor interaction causing the cycling.

5) If the boiler display shows flow sensor or temperature sensor related codes (260, E2, E9 variants), do not attempt sensor replacement yourself. Note these codes and call an engineer — sensor faults will often cause incorrect temperature feedback and modulation issues.

6) Check for rapid demands: the GB162 has a switch optimisation that can prevent immediate restart if the burner has been started more often than a set frequency. If you observe very frequent short demands (e.g., under 10 minutes between starts) this optimisation may be engaged. An engineer can review and adjust control settings or diagnose why the system is short-cycling.

When to call a professional and what to expect:

- Call a Gas Safe registered engineer if the basic checks above do not stop the frequent partial-load cycling, if you see additional fault codes, if the boiler pressure is repeatedly low, or if the pump, valves or sensors appear faulty. Also call an engineer if you are not comfortable changing boiler settings.

- The engineer will check system hydraulics (pump speed, airlocks, flow/return temperatures, zone valves), examine sensor readings and wiring (flow, safety and flue sensors), inspect the burner control unit and KIM/UBA modules, review switch-optimisation behaviour and adjust setpoints or controls, and replace defective parts if required.

- Do not attempt internal electronic, gas valve, ignition or sensor repairs yourself. These require qualified diagnostics and safe replacement by a registered professional.

Summary note: Error 265 is usually a non-critical operational message telling you the boiler is modulating and waiting due to the pattern of heat demand. It can point to control or system imbalance that affects efficiency and component life. Carry out the safe homeowner checks listed above; if the issue persists or other fault codes are shown, have a Gas Safe engineer diagnose and correct the underlying cause.