Boiler runs but radiators do not get hot or only partially heat up, no error code displayed.

Safety first: Radiators and pipes may be hot. Use a cloth when bleeding radiators to avoid scalds.

User-level checks:

• Bleed all radiators starting from the lowest floor; top up system pressure afterwards.
• Ensure all TRVs and lockshield valves are open.
• Check that the room thermostat is set high enough and that time controls are calling for heat.

Technical checks (qualified personnel):

• Check pump operation and speed setting; increase speed if necessary.
• Inspect and clean any system filter or magnetic filter on the return line.
• Consider powerflushing the system if sludge is severe.
• Balance the radiators by adjusting lockshield valves to ensure even heat distribution.

After improvements, verify that all radiators reach target temperature within a reasonable time.