UFH manifold TMV control

12 Nov 2010
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United Kingdom
I have a problem with a new installed UFH system as follows.
One 46kW oil boiler heating two number 12 port manifolds plus DHW and rads and I am having difficulty controlling the TMV on both manifolds.
Having set both manifold mixing valves to around 45* the TMVs don't hold that temp.they both increase in value up to 55/60*
The floor temp probes are turning off the room stat. (protecting wood and tiled floor)
The fact this is on two seperate manifolds suggests the fault is not with an individual TMV
The common denominator is the boiler? or is there something else I have missed
Paul C
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The common denominator is the boiler? or is there something else I have missed
Yes, the person who installed them making an error in the pipework.

Tmv heating flow and ufh return are likely coming in backwards. This could be due to the pump misconnection or other misconnection
Thanks for the response.
The UFH kit was supplied by underfloorheating1.co.uk at Carcroft Doncaster
I have not got the details of the TMV manufacture but there is a photo attached showing the System installed.
I have checked the flow & return circuit and all seems ok.
Looking at the attached photo the flow pipe from the boiler is on the left (in the picture) going into the underside of the mixing valve.
The two horizontal ports of the mixing valve are stamped "C" (cold) on the casting, accepting return water from the bottom manifold then into the boiler return pipe (RH vertical copper pipe)
The manifold side TMV port being bigger (25mm) than the boiler return pipe (22mm) if that sounds right
The pump arrow for flow is directed towards the top manifold.
So piping up seems to be in order.
Where does the above take me next??


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All sounds fine, the two horizontal connections are both the same as you can fit left or right hand. When new water is introduced from the boiler by the tmv, the cooler water is forced back along there, otherwise it keeps going round.
Try turning the tmv to minimum.
Could be a faulty batch of valves or grit in the system stopping them closing.
As said try turning the tmv lower.
The number scale on the knob won't necessarily be calibrated accurately to the actual temperature the valve discharges.
Check the arrow on the back of the pump casting. Normally underfloor heating pumps are inverted.
One valve has settled down at 46* (the height of the spindle protruding the valve casing measures 5mm) and working ok.
The other, with the valve set to minimum, is at 56* (spindle fully in and is 3mm from valve casing)
The pump arrow is showing correct direction, pumping water to the "hot" manifold
I am beginning to think this valve(s) were subjected to some grit which has possibly left this one valve damaged.
There is a Furnox Omega filter installed on the return pipe protecting the boiler but as I said earlier this problem could have been on since the heating was turned on, last Dec.
Should be Y strainers fitted to the inlet of the blenders.
Like this....

With isolating valves fitted to allow periodic maintenance.

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