clunking noise soon after I start or stop the radiators

The condensate pipe is probably blocked

This could be a few things depending on the system and boiler you have. This problem though is most likely caused by either: 1) Lack of water pressure and/or air- If its a pressurised system, make sure the pressure gauge is showing the system is topped up to 1 bar and vented. If Its not pressurised someone needs to check the system is filling from the feed and expansion tank. 2) Build up of heat- This can be caused by a faulty thermostat depending on the age and type of boiler. Turn down the thermostat and see if its still making the same noises. It could also be caused by a worn heating pump or diverter valve sticking but hard to say without knowing the system. 3) Scale and debris in the system- Depending on the system this can be solved with a chemical or powerflush. I would then advise fitting a magnetic filter if there isn't one already fitted on the return to the boiler. I would advise getting a heating engineer in who will quickly be able to identify the type of system and boiler you have and advise accordingly.

Possibly low pressure or expansion vessel needs charging or system needs bleeding. Boiler would not run at all if blocked condense.

Hi there, I suspect that this is is down to 1 of the 3 things- - limescaled heat exchanger (if you don't have a scale reducer on the cold mains) - rust/sludge in the heating system (if you do not have a magnetic filter) - or air in the radiators (if the radiators haven't been bleed in a while) If neither or the above, then I would suggest having the boiler serviced. Regards, Chris