Boiler runs but radiators do not get hot, or only partially heat, while hot water may still work on combi models.

How to Fix / Troubleshooting

Safety first: Allow system to cool before bleeding radiators or touching valves.

Homeowner checks:

Ensure the room thermostat is turned up and any programmer is set to heating ON.
Bleed radiators to remove air and then top up system pressure.
Check that any manual valves near the boiler and on the system are open.

Engineer actions:

Check pump operation and verify flow/return temperatures; replace the Worcester pump head if not circulating.
Inspect and free or replace the diverter valve if stuck in DHW position.
Clean or replace any system filter and consider a powerflush if sludge is present.

Restoring proper circulation will improve heating performance and protect the boiler from overheating.