I have an Ariston boiler. This is in London in a 4 bedroom house - bought the house 3 years ago. teh boiler was installed in 2000. we have had homecare agreement with BG since we moved here. boiler has been having problems from time to time - has parts replaced and continues to work. last week it started making very loud noises - called BG - engineer came drained the large red device at the back & said very black water system will need powerflush at some point but it is fixed for now. after he left i noticed the boiler wasnt working - called BG again - different engr arrived & found a rubber tube at the top had burnt off so replaced it & said it is ok for now. after he left when the hot water was used the boiler started making loud noises again. same engineer coems back & says that 2 valves under the boiler need replacing but the system needs powerflush cost £699. if i dont have it done the boiler will keep getting clogged. he will come back next week to replace valves but says not sure if the system will work as it is clogged with sludge. i am not sure whether to do the powerflush as it will not resolve the cause just the symptom. the sludge seems to have suddenly appeared into the system as no engineer has raised teh issue before and there have been visits at least one every year. if someone can help i will be very grateful. I am trying to get a second opinion next week - any advice re the questions that i should ask etc will be very helpful. Many thanks