Why does the water run hot forever through my bathromm and kitchen faucets but I run out of hot water after 5 minutes in the shower? My boiler is only 10 years old.

Part of the answer is "flow". You have a lot more water passing through the shower or bathtub then you do the sinks. So if you have a finite amount of hot water then your going to use it up much faster then you would in a sink.

Part of the answer if "flow". You have alot more water passing through the shower or bathtub then you do the sinks. So if you have a finite amount of hot water then your going to use it up much faster then you would in a sink.

I hear you but this situation has only been happening for the last year. The previous 8 was fine.

Kitchen and bathroom sinks have water flow of about 1.2 - 2.2 gallons per minute. Your bath tub and shower (with non-low flow shower head) runs water at 4 -8 gallons per minute. So you do the math: with 40 gln hot water heater it will take about 5 minutes before you run completely out of hot water as opposed to 33 minutes of hot water in your sink. Solution: use low flow shower heads.

I hear you but this situation has only been happening for the last year. The previous 8 was fine.

Tom, Milo, Dad

Could a deteriorated or broken dip tube cause this?

I'd say yes to the diptube and so could increased water pressure and so could a defective cartridge, but the defective cartridge would only affect a single fixture.

A remote possibility is a single lever faucet causing a cross connection but again, this would probably be everywhere.

Test:
Turn off the cold water at the stop and see if you get hot water longer. You can't take a shower with no cold during the test.

Tom, Milo, Dad

Could a deteriorated or broken dip tube cause this?

I don't even know what that is or what it looks like. You would have to describe it to me and tell me where its at.

Under the cold water pipe fitting there is a plastic tube inside the tank that takes the incoming cold water to the bottom of the tank.
The hot water going out of the heater is taken from the top.

If tube is broken cold water coming in can just go out the hot water side.
See this web site (http://www.ronhazelton.com/archives/tips/repair_broken_dip_tube.shtm)

I'll give the shower valve as the first suspect. So, turn off the cold water at the shutoff to the shower and see how much hot water you get.

I give up