First I'd like to apologize my 'B' key is messed up so it dont always work and I dont always catch it. My boyfriend uses a wood boiler with his radiant floor heat in the garage, he only has one zone with four loops.. Currently he is using a 007 Taco pump. the garage is about 24'x50' and the return lines dont get as warm as they should. We are unsure of what the problem is and have been researching it. He turned one of the loops off and the other three got warmer, and if he shuts off two loops the other two get up to the proper temp. Also the loops are 300' each, 1/2" PEX tubing was used. Any ideas what could e wrong?