My mother has had quotes in for replacing her existing regular system boiler with a Worcester Bosch Greenstar Ri15. The heating engineer who she would like to instruct has said he will charge approximately an extra £550 for taking out tanks, changing pipework if she wants a combi system (which neighbours are telling her to do). If she has a combi installed, will a single person easily recupe the extra £550 over say £10/15 years? Alternatively, if anyone has any idea how much it costs to heat a cylinder that might help - she runs approx 2 baths, 5 showers and 2 washing machines loads off the cylinder weekly, as well as general washing up.