recently had to have the heat exchanger replaced in the boiler due to build up sludge, luckily insurance covered the cost but has now told us to have system flushed before they will cover any further repairs. We had the boiler fitted nearly 8yrs ago onto existing radiators and pipework. The radiators and pipework are quite old and used to work via coal fired central heating when we moved into house 10 yrs ago. Wondered what type of sludge remover and inhibitor anyone would suggest for an older system as i can't afford to replace the lot but want to minimize chance of leaks after having system flushed