After a complete system clean out my boiler is making loud popping noises with fluctuating pressure when the hot water is on but only at high hot water flow rates. Thermisters all OK and the gas modulates with the temperature knob but doesn't seem to modulate when the water comes up to temperature .. loud pops and bangs ???

ChrisH, February 2009

boiler main heatexchanger may have scale inside. gess

Mr K, February 2009