UFH mixing valve not restricting heat to floor

[Dtwone]

Can you sketch how you’ve tapped into the heating pipework that serves the flow to the manifold. Was you aware the cylinder return is always the last tee in?

I was just trying to sketch that hope the edited photo makes sense, yellow line is T down to Ufh 2 port downstairs. Green is 10mm to bathroom rad. Dark blue is HW tank feed through 2 port and light blue is to rads via the other 2 port there in the airing cupboard.
I don't know where the cylinder return is as its under the floor upstairs somewhere.

 

[Sharp Point]

Have you removed the tmv white plastic knob, to see if it’s engaging the brass spindle? Maybe try turning spindle with a spanner/ grips/ pliers

 

[Dtwone]

Have you removed the tmv white plastic knob, to see if it’s engaging the brass spindle? Maybe try turning spindle with a spanner/ grips/ pliers

I've taken that off, the tap operates fine and the stat and Spring behind it have been replaced with a new tested stat, the system was well flushed and there was nothing in the mixing valve body when I took it apart to change the stat, spotless.

Why should the Ufh return to boiler being last be a problem, I've had all 3 zones on as well as HW or Ufh only and everything works fine it's just the mixing valve doesn't seem to be restricting the hot flow from the boiler??

Attached a pic of the mixing valve adjuster and thermostat, strange little unit that allows flow from H flow in to mixer across to the C outlet when it gets to about 30 degrees

 

[Sharp Point]

I've taken that off, the tap operates fine and the stat and Spring behind it have been replaced with a new tested stat, the system was well flushed and there was nothing in the mixing valve body when I took it apart to change the stat, spotless.

Why should the Ufh return to boiler being last be a problem, I've had all 3 zones on as well as HW or Ufh only and everything works fine it's just the mixing valve doesn't seem to be restricting the hot flow from the boiler??

I haven’t said YET it’s a problem, I merely asked if you were aware. Over the years I have come across flow problems, because the cylinder tee wasn’t the last tee in.
It’s quite difficult to give you a solution, when there’s a hundred answers we need to know. You clearly have practical skills and commend you on that, but sometimes the tiniest things can be forgotten to be mentioned that could solve a mystery.

 

[Sharp Point]

Also, how are you measuring the deltaT, are you relying on the gauges or are you using a known accurate device? Those mechanical gauges are usually pants and don’t give a true reading.

 

[Dtwone]

Sorry if I come across abrupt in any questions, i don't mean to be. I've read up a lot and absorbed lots of info from suppliers and tradespeople. I'm a rather over enthusiastic diyer but I like a challenge and have just built the entire extension bar the electrics and boiler flue change, I can almost solder neatly now too just signed off by building control so I'm pretty chuffed, just annoying about this flow mixing business.
I've an IR thermometer that gives a pretty much identical reading off the matt black back of the Ufh pump and the pipes to the floor feel too hot to hold when the Ufh inlet gauge gets to 60, so I'm pretty sure they are quite accurate, values also tally on boiler feed and return pipes so I'm happy it's not just a reading issue.

 

[Sharp Point]

What about the ufh return pipes coming out of the ground, do they get hot too?

 

[Dtwone]

What about the ufh return pipes coming out of the ground, do they get hot too?

Yep, after 10 minutes of 60 degree heat going in the return gauge is up to over 40 degrees and the barrier pipe coming out of the floor, both loops, feels quite warm to the touch, far warmer than they should I think,it heats the floor lovely but it's doing it far too quickly and with too warm flow in

 

[Ric2013]

Well, yes, ideally you would tee back in the same order you have teed off, but I would not be pointing the finger at that item either. Although I find the airing cupboard is a bit too messy to understand without running my fingers along the pipes and pointing, I'm yet to see anything obviously wrong, so long as the flow and return are not swapped over.
The UFH pump is definitely pumping upwards, yes? (Check the arrow moulded into casting).

 

[Chuck]

Yep, after 10 minutes of 60 degree heat going in the return gauge is up to over 40 degrees and the barrier pipe coming out of the floor, both loops, feels quite warm to the touch, far warmer than they should I think,it heats the floor lovely but it's doing it far too quickly and with too warm flow in

I haven't read the whole thread in detail, but it seems to me that the water is being circulated through the UFH emitters too fast. This means it doesn't have time to cool enough to be able to reduce the the incoming flow to the correct temperature in the mixing valve. This will give a runaway effect where for the first few minutes the water going to the UFH emitters is the right temperature but it then ramps up until the mixer is ineffective at cooling the incoming flow.

If I'm right, the remedy is to reduce the circulation by turning down the pump and/or the balancing valves on the UFH emitters.

Whoever designed the system should have calculated the circulation rate and matched it to the amount of power that the UFH needs to emit.