Radiant Heat Install Problems

Hello All

All input and suggestions are appreciated. Dealing with a sort of head scratcher.

We took out an existing gas fired cast iron boiler that was doing 3 radiant zones and one first floor radiator zone and installed a Weil-McLain ECOTEC with a buffer tank. We removed the radiators on the 1st floor at the customers request and installed Rehau heat transfer panels under the subfloor with a new 5 port manifold. It came out to 5 loops with 1/2” tubing - all loops under 250ft with no joints. We also replaced the (3) existing radiant manifold with new like-for-like manifolds.

Upon purging and starting the boiler, the new first floor loop heated beautifully. All plates got warm and water was mixing well through the Caleffi mixing valves. However, when turning on the other zones, it seemed as if all of the mixing valves suddenly closed. I was unable to get hot water to move through the mixing valves. The pump body’s were all screaming hot. I got on the phone with Caleffi tech support and really got no where. He suggested I might’ve used the incorrect valve for the application despite the tech documents stating that they were suitable for hydronic heating. Anyways, today I removed the Caleffi mixing valves and replaced them with Taco mixing valves and still got the same result. The new first floor loop was heating, however all of the existing radiant will not heat and the water is not flowing through the mixing valve. Red hot up the hot side of the valve, ice cold on the other side, pump is running There is no air in the system as I relentlessly purged each manifold several times.

I’ve attached a picture of the near boiler piping and basic drawing on flat paper of what it looks like. Let me know if you guys see anything or have any suggestions on what to check. Thanks!!

Disclaimer boiler install was not finished when these pictures were taken.