System OK , but during operation at startup and regularily thru operation , loud noises kick in for 5-10minutes. Every hour or so ? CH system (expansion tank) was run down , Femox type flushing compound added, System run for some days , flushed again, and corrosion inhibitor& and boiler noise cure compound added. System going well and better heat from radiators after bleedingoff air, but noise persists.
What could be the problem and cure?

George Aberdeen, March 2010

If boiler is making a banging noise known as "explosive ignition!" this is due to hairline crack in the burner lower manifold tube or tube is loose allowing escape of gas within the boiler chamber that ignites with a delay & combust very loudly. This part is expensive. Circa £145 + vat. The part can be repaired by using Holts "Firegum" (plyable joint sealer paste) that rub over joint & can withstand temperatures of 1200 C & with heat bond becomes stronger.

Tarquin, February 2012

check the pump, if you've had problems with sludge then you may have some debris lodged in the impellars.

Ian, March 2010