Hi @shrimohanyv
Check if the thermal paste on the CPU needs refreshing as it may have dried out and become less effective.
Presumably, when the fan was replaced, the condition of the thermal paste wasn't checked as it isn't necessary to remove the heat sink from the CPU when just replacing the fan.
Here's the [https://kaas.hpcloud.hp.com/pdf-public/pdf_12632864_en-US-1.pdf|maintenance and service guide], taken from this support [https://support.hp.com/us-en/product/setup-user-guides/hp-15-db1000-laptop-pc/model/33679650|webpage] for the laptop.
Go to p.57 (67 of 105 pdf) in the guide to view the procedure to remove/replace the heat sink assembly.
Here's the ifixit [guide|744] guide that may also help.