Had the same problem. The bilge filled with blue coolant from the engine expansion tank. The boiler cannot be repaired and must be replaced. This is a fairly simple job but on our 44 we had to rebuild / modify the seating. We also fitted two valves on the engine to isolate the boiler from the engine cooling circuit if the new boiler should bust in the future. Our leak was caused by ice due to the previous owner not draining the system. Essential every winter.
The membership association for owners of Dufour Yachts