We recently moved into a home, the water heater is 9 years old. We get hot water to sinks (although not as hot as it has been in the past) but the shower water is definitely chilly. We have 2 showers, one upstairs, and one down, and both are equally affected. How can one tell if it is a water heater problem.. and what to do?

Is it electric or gas/LP heater
Electric heaters are a little slow on heating(in my experience)and might have a hard time keeping up with use.
Gas/LP heaters are more efficient and might just need cleaned,adjusted(the red knob on the front)to a higher setting,etc.
I would suggest a call to a local handyman and get their advice before buying a new system.

Check The Pipes That Are Going Directly Into The Tank U Possible May Have A Hole It May Be Leaking Where U Don't Know. Have Had This Prob. It Was Always The Same Thing A Small Hole In Pipe Or Pipes In Bsmt Or Crawl Space.

Also Should U Need Ur Pipes Replaced Go With The Plastic Ones Instead Of Copper