What would happen if I connected my UFH mixing valve with flow and return the wrong way round?

[puffafish]

I have a UFH mixing valve similar to this: https://www.theunderfloorheatingsto...H437-KKs4sLEkYb6B9EoV_FiJdBhmEYgaAke1EALw_wcB

I have a suspicion that the flow and return pipes are labelled the wrong way round as the return is often warmer than the flow.

Unfortunately I can't trace the pipes, so can't prove if they are labelled backwards or not.

 

[Johntheo5]

I would think you would just keep reirculating cold water around the manifold.

 

[Madrab]

Simply put - Your UFH wont work.

If you can get to the mixing valve then the pipe coming in at the bottom should always be hotter than the one above it - depending on how the system is set - HW temps from the boiler - UFH system temp settings etc will determine how much but it should always be hotter. The pipes can't be mislabelled as they should be stamped with F & R, if they've bee fitted correctly that it.

Who fitted it and when?

 

[puffafish]

The flow and return pipes were put in and labelled nearly ten years ago. The rest of the connections about 4 years ago.

The flow pipe takes longer to warm up than the return. The return pipe gets hot almost instantly.

There is flow through my UFH if I set the mixing valve temperature to around 30-35C, any hotter and it gives no flow.

 

[Johntheo5]

With this flow at 30/35 setting, is there hot water going to the mixing valve from the port marked H or is it just cold water circulating?.

 

[puffafish]

With this flow at 30/35 setting, is there hot water going to the mixing valve from the port marked H or is it just cold water circulating?.

The port marked H is cold, the port marked C gets hot. After a while the port marked H gets warmer

 

[Johntheo5]

If the CH is also on then you might be pulling (warm) return water through with the manifold pump, maybe break the cold (which may be the hot supply) and run oiff a 5 litres or so that might identify it or do vica versa.

 

[puffafish]

I bit the bullet and swapped flow and return. The system is now working and responding exactly how it should do. So it appears my flow and return were labeled incorrectly all those years ago and it's be just about getting slightly warm since then. This explains a lot of other issues I've had with the UFH as well.