UFH: is my water temperature mixer working?

[nickldntw]

My UFH was installed about 5 years ago and runs from a Vaillant combi boiler.

One issue I have never been able to sort out is the water temperature adjustment for the UFH. There is a valve to control the UFH water temperature by blending hot water from the combi with cooler water from the UFH pipework. But it doesn't seem to work, floor gets very hot if the boiler flow temperature is set high.

When I set the dial on the UFH to 45 degrees, the temp indicator above the pump matches the boiler flow water temp. Picture shows almost 60 degrees, which is too much.

As a workaround I turn the combi temp down to about 45 degrees, but that's not ideal.

Am I interpreting this dial correctly? It's after the mixer pump in the water circuit, so should read the adjusted temp as set on the dial, in this case 45 degrees?

What do I need to do to stop needing to adjust the combi flow temperature and to get the UFH to do that?

 

[Johntheo5]

Yes, the temperature gauge above the pump should read close to the index setting on the mixing valve, the valve shuttle may be stuck, turn the adjusting knob up and down fully a few times then set it to say 30/35C, if it now controls at around this temperature then gradually increase the boiler flow temperature to its normal setting and re adjust the mixing valve setting to "normal".

 

[Johntheo5]

If its never worked properly, check the mixing valve, there may/should be H on the left hand port and C on the right hand port, also check that the arrow on the pump body is pointing upwards.

 

[nickldntw]

Thanks for your responses. It seems to be fitted in accordance with the instructions. The only thing I'm not sure about is if it's been bled correctly at the pump.

I have been doing some tests with the boiler flow water temperature and the top of the manifold (red tap) gets as hot as the incoming water from the boiler. The temperature on the dial in the top section closely follows the boiler, even after an hour to allow the system to balance.

I assume this is wrong and the mixer valve should cool down the water from the boiler before it gets to the top part of the manifold?

 

[Johntheo5]

Looks like the mixing valve isnt working, yes it should mix the cold return water with the hot boiler water to give you a blended temperature to the top manifold, what make is the blending valve?

 

[nickldntw]

No idea of the make, but it's sold here:

Thermostatic Mixing Valve - The Underfloor Heating Company

Our compact and lightweight underfloor heating thermostatic mixing controller is easily connected to the underfloor heating manifold

www.theunderfloorheatingcompany.co.uk

 

[Johntheo5]

Seems plumbed up correctly as per spec in your attachment so looks like the TMV is the culprit allright.

 

[nickldntw]

Shame, I will need to put that right as it's very annoying changing the flow temperature at the combi boiler. Also not sure how efficient it is with running a 40-45 degree water temperature with combi.

 

[nickldntw]

Perhaps the mixing valve can't do its job because the flow rate is set too high. My 23m sq system is set to about 3 litres per minute.

Does that seem right?