I get hot water in my sinks and shower in my master bathroom, but water is only hot for a couple seconds when I turn on the hot valve in the tub. It has separate handles for hot and cold water. I have a recirculating pump on the line and the hot water tank is on the opposite side of the house. Any ideas?

Is the pump running?
Feel the return line at the water heater. It should feel slightly warm. When you open the tub valve does the return line still feel warm?
Do you have a stop valve on the return line at the water heater.

Yes. The pump is running. I'm not sure what a stop valve is at the water heater. The return line after I ran the tub for 15-20 seconds was cold. The water ran hot at the tub for about 5-6 seconds before it starting turning warm at best. Z

A stop valve is a on/off valve in the return line that you can stop the flow of water. Does your return line connect to the cold water input line or the bottom of the water heater?

Sounds like you circulation pump has failed. If the circulation pump motor is running, the impeller blade has come loose from the motor shaft.

When you use hot water, hot water comes up through the hot water line, but cold water is also drawn up through the return line.

You can confirm that the circulation pump is failing by stopping the flow in the return line. You should then get hot water out the faucet.

What kind of pipe, copper of CPVC?

Yes. There is a stop( ball valve) on both sides of the recirc pump. It ties into the cold water input line. The pipe is copper. So should I turn of the pump and close the ball valve to see what happens?

Just close the valve. You should then have hot water at all faucets. Not instant. Take a few seconds for the hot to reach the faucet. If that's what happens then the pump is bad.
I have two story home with water heater in basement. I have recirculation line from master bath, upper floor, back to cold water input on water heater. When I built, I put a recirculation pump in. After a few years the pump failed. I removed it and reconnected return line until I could replace pump. I then noticed that the system still worked. Gravity made hot water rise and cold water fall. A siphon action at the tee where return line tees into the cold water also draws water from the return line whenever cold make up water goes into water heater. I now have a gravity system that doesn't cost me the use of the pump.

If you have multi-story home with water heater in basement or lower floors, you might try gravity system. Just remove pump, put in a piece of pipe with a check valve and see if it works.

I will try this when I get home. Thank you very much.

Thank you for your help. It appears the recirc pump is bad because when I turn it off and shut the valve, I get plenty of hot water at the bathtub in the opposite end of the house. I live in a single story house, so I don't think the gravity option will work. Again, thank you.

Thanks for the feed back.