2 broken valve inserts in a row

[domib13]

I'd like to ask for your help regarding my underfloor heating system.

We recently moved into a new house (about six months old), and within the past few weeks, two valve inserts in the manifold have already broken. I'm feeling very frustrated.

The heating system was initially quite basic: manual knobs on the valves, a single thermostat in the living area, a gas boiler, and a circulation pump.

The first issue occurred when I tried to reduce the flow in the living area to allow for higher flow in the more distant rooms. I almost closed the valve when it suddenly broke. (The plumber didn't have a replacement valve insert, so they installed a temporary plug instead.)

After that, I decided to upgrade the system by installing actuators (Möhlenhoff Alpha-5) on the valves and integrating the control system with Home Assistant. This allowed me to control the temperature separately in different rooms. It worked well for a few hours, but then another valve insert broke while it was closed by the actuator for several hours—this time on the valve right next to the one that had already failed.

Do you have any tips or ideas as to why this might be happening?
Could it be due to poor material quality, improper installation, or perhaps a design issue?
I’d really appreciate any thoughts or advice on this!

 

[cross thread]

Either very poor quality or over tightening, they are on a o ring seal so only need nipping up.

 

[opps]

I believe that the granular nature of the break suggests that it was badly cast.