2 port valve for underfloor heating

[dogbower]

I have underfloor heating downstairs and radiators upstairs.
Each floor has a 2 port valve on the flow so can work independently from each other.
Just wondering why the flow to the underfloor heating needs a valve to it.
If the underfloor heating thermostats aren't calling for heat all the actuators on the manifold would be closed anyway, so no flow.
Thanks Stuart.

 

[Norcon]

It doesn't need a 2 port valve when manifold actuaters are fitted.

It will prevent backflow through the tmv. Though a better option is available.

 

[dogbower]

Thanks norcon, what would the better option be?

 

[Norcon]

A non return valve on the tmv by pass.
You've no need to do anything as when the ufh is off the back flow path is shut.

 

[knuckles]

It is not to prevent backflow. The two port valve closes flow through the TMV and straight back to the return. With no demand for the underfloor, the valve will get to temperature and open the path to the boiler return.

 

[Agile]

The installer also often uses the two port valve as a relay to give a call for heat to the boiler!

Most UFH circuits also have a dedicated pump operating with the TMV.

Tony

 

[Norcon]

It is not to prevent backflow. The two port valve closes flow through the TMV and straight back to the return. With no demand for the underfloor, the valve will get to temperature and open the path to the boiler return.

The point is when you have actuaters on the manifold then no zv needed.

However when the ufh is off and upstairs rads or HW on then a parasitic back flow will occur through the tmv. Been there and got the T shirt.