Hard brakes on ldv van

My partner is having problems with braking in his ldv van. It started a couple of days ago, he went to brake but brake pedal was really hard to push down and braking was slow. He said he heard a hiss when it first happened not sure if this has anything to do with the problem.

Perfect description of a power brake boster failure. What’s a Idv van?

Check the vacuum hose for the brake booster.

One test is to shut engine off and push brake pedal firmly several times. Brake pedal travel should diminish with each push until it hardly wants to move at all. If you get the same minimal travel from push one to push four, the brake booster has failed. There are other tests and the Haynes manual should have the ones peculiar to your vehicle.