We have an Ideal ISAR combi, approx 7 years old. To be honest it's been nothing but trouble. It's let us down on numerous occasions for various faults. Fortunately, we have never had any trouble getting CORGI registered fitters to look at it. In terms of how long combi boilers last, I think it's going to be difficult to put a figure on it. Not all combi boliers are the same and economic longevity is likely to depend on a number of factors such as water quality, hardness, how heavily stressed it is - i.e. do you have a small boiler trying to heat a big house to a high temperature? As for the economics of repair versus replacement, if you're seeing infrequent bills of £50-60 that might be tolerable, but if you're staring at £300+ it could be time to consider replacement.