The hydraulic pump on the right engine of the Reims Cessna F406 Caravan II had been replaced at Lorient Airport in France. The airplane was taken on a post-maintenance test flight. The crew flew a go around with a simulated engine failure. When the undercarriage was raised, the “HYD PRESS ON” light went out and the red “GEAR UNLOCK” illuminated. When accomplishing the associated procedure for this fault, the crew heard a ‘thump’ and vibrations were felt. They continued to select the undercarriage down but just two greens showed up. The indicator for the nose landing gear remained red. The “HYD PRESS ON” light is now illuminated (amber) along with “GEAR UNLOCK” (red). To stop pressurizing the hydraulic system of the undercarriage, the pilot flying pulled the breaker “LDG GEAR”, causing the “HYD PRESS ON” to go off. Additional attempts were made to get the nose gear down, among others by using g forces. A low pass over the airfield confirmed that the nose gear was still retracted. The flight crew then decided to enter a holding pattern to burn fuel. After holding for 90 minutes the decision was made to carry out a forced landing with 800 lb of fuel remaining because weather was deteriorating. A safe nose gear-up landing was made on runway 20 with the aircraft coming to rest after less than 500 m. There was no fire. Damage to the nose and both propellers was substantial. Causes (translated from French): The event was a blockage of the nose landing gear caused by the overlapping of two landing gear doors of the front undercarriage. The cause was the design of the forward undercarriage box allowing the landing gear to retract higher than expected in special operating conditions.