The water is luke warm and the pressure is lower than ususal.

We probably need more information to give a good answer.
You report 2 different problems occurring at once: Low pressure and Low temperature.
If this is tankless water heater, then Low pressure and Low temperature might be related, and you probably need a service technician to diagnose and repair cause.

If this is tank-type water heater, look at label on side of tank for type and brand of heater.
Is it gas or electric water heater? Troubleshooting is totally different for each.

Is water pressure pressure low on just the hot side faucet, or is cold side faucet affected too?
Are all hot faucets affected by low pressure?
If you have a dual handle faucet, open hot side only and check if hot water that comes out is hot as normal.
This will say if problem is pressure or temperature.
Tank-type water heater usually won't have both these problems occur at one time, but water heaters work in funny ways sometimes.

Add a comment to this post, or re-post your question with details so the experts can give a solid answer and not guess.
Also you can post water heater questions on pro water heater forum:
http://www.thetankatwaterheaterrescue.com/forums/forum3/

Add a comment for more free help.
Also take advantage of fixya phone service.
For a price, expert speaks with you over phone while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.