I just replaced a 50 gallon natural gas water heater with a new Whirlpool of the same size and specifications.

We have a Laing 303 recirculating pump on a timer.

I've checked and rechecked all the connections, hot to hot cold to cold, thermostat temp, dip tube is not broken. I get plenty of hot water at all of the faucets in the house for several minutes, but I'm getting 2-5 minutes only (before it turns cold) in the showers. The first floor master shower has a newish 5 years old Moen single handle faucet. The second floor tub showers all have 20 year old builder grade faucet sets.

The sinks in those baths run hot for a very long time, but the showers run out within a few minutes.

One thing I noticed when someone was running the master bath shower is that the water supply line into the recirc. Pump goes from hot to the touch to cold quickly. The pump feels like it's moving water. Is that normal ? Seems like the water should be coming through that line warm to the touch as it's the recycled hot water. I'm completely baffled. HELP!!