Pureit / Hindustan Unilever — Marvella RO+UV Circuit failure issue

3 days back I called the service person to change the GKK-2 filter kit worth 3500 rupees. He changed and immediately, all the lights have turned red. I called that person again and he said circuit has failed you have to now replace it with new circuit which costs another 3500 rupees. I clearly understand circuit failures do not happen unless service person has intentionally done something to make extra money. Why company is selling the products with such loopholes and why as a customer I should bear the losses?