I have a Laing re-circulation system near my water heater running once every 45 minutes which is fine and water is hot at all faucets. The system is such that about halfway down the hot water feed line there is a T which sends water to the upstairs bathroom and to the first floor kitchen. The re- circulation return line comes off the feed to the kitchen. My problem is that when the upstairs bathroom whirlpool tub is being filled (it's a big tub) the kitchen gets only cold water for many minutes instead of immediate hot water. The return line from the kitchen faucet has the following: a shutoff valve, pump, hose bibb, check valve, air vent, shutoff valve and back to where cold water enters water heater in that order. What would cause the kitchen faucet to run cold when the upstairs tub is being filled?.