Blocked Central Heating Pipes -

: The boiler may overheat, cycle on and off frequently, or display error codes and lock out.

I don;t know which is best, but I understand the latest ones work by both magnetic and 'swirling' out sediment (like a Dyson). It' Screwfix Community Forum blocked central heating pipes

For minor blockages, chemical cleaning agents can be added to the system via the radiator or a filling loop. These chemicals break down sludge and scale, allowing them to be dispersed. However, this is often a temporary fix for heavily blocked systems. : The boiler may overheat, cycle on and