nickldn Posted February 12 Share Posted February 12 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? Link to comment Share on other sites More sharing options...
dpmiller Posted February 12 Share Posted February 12 So the white knob on the mixer is set to 45 yes, but... a. that's the return temperature so hot flow will enter the UFH until the return warms up to 45 b. the knob is adjustable for calibration and may not even be set right. c. are you sure the gauge is accurate? Does it read ambient when the heating has been off for some time? Turn it down to 35- or 30 even- and watch what happens when the system stabilises. Link to comment Share on other sites More sharing options...
ProDave Posted February 12 Share Posted February 12 Has it EVER worked properly e.g. when first installed? Can you post a picture zoomed out a bit and tell us which pipe is the flow from the boiler and which is return? If you don't know, turn on the heating from cold and the first pipe to get hot is the flow. Link to comment Share on other sites More sharing options...
nickldn Posted February 12 Author Share Posted February 12 Thanks for your replies. I have uploaded a zoomed out photo, the pipe with the blue valve motor box on it is the flow from the combi boiler. The return is the pipe next to it with the red earthing tag. If I get water at 60 degrees from the boiler, it remains at 60 degrees in the upper (red) part of the manifold, which gets very warm to the touch. The bottom (blue) part of the manifold stays much cooler (but is still warm to the touch of course). Gauge does read ambient after some time and matches flow temperature from boiler accurately, so I think it's fine. Having read your helpful comments am I right in thinking the dial adjusts the return temperature, so I should expect to the top (red) part of the manifold to be the same temperature as the boiler flow and the bottom (blue) part to be the temp of the actual water going through the UFH? If so that's what's happening I think. Link to comment Share on other sites More sharing options...
nickldn Posted February 12 Author Share Posted February 12 Link to comment Share on other sites More sharing options...
ProDave Posted February 12 Share Posted February 12 You have the same, or very similar manifold to me, and the flow and return are correct Here is mine: the blending valve should adjust the flow temperature, i.e. the temperature shown on the gauge above the pump. Turn your mixing valve all the way it will go clockwise until it comes against a stop. If that does not reduce the temperature then the blending valve is faulty. Link to comment Share on other sites More sharing options...
nickldn Posted February 12 Author Share Posted February 12 So just to be totally clear does your gauge at the top show the blended water temperature, so when you turn your blending valve clockwise the temperature reduces? Or does it show the flow temperature from the boiler before it's been blended? Sorry for being dense here. Link to comment Share on other sites More sharing options...
ProDave Posted February 12 Share Posted February 12 25 minutes ago, nickldn said: So just to be totally clear does your gauge at the top show the blended water temperature, so when you turn your blending valve clockwise the temperature reduces? Or does it show the flow temperature from the boiler before it's been blended? Sorry for being dense here. It should show the blended water temperature. It won't go down instantly, it will need the heat to be lost to the UFH loops to cool it down so it will take a while for a change to the dial to show on the gauge. Link to comment Share on other sites More sharing options...
John Carroll Posted February 13 Share Posted February 13 (edited) 16 hours ago, ProDave said: You have the same, or very similar manifold to me, and the flow and return are correct Here is mine: the blending valve should adjust the flow temperature, i.e. the temperature shown on the gauge above the pump. Turn your mixing valve all the way it will go clockwise until it comes against a stop. If that does not reduce the temperature then the blending valve is faulty. Are you saying the pipe marked "flow"is the hot supply to the mixer?, thought that might be the manifold cold return to the boiler, if the flow is as shown then the Mot. valve is on the return?. Edited February 13 by John Carroll Link to comment Share on other sites More sharing options...
ProDave Posted February 13 Share Posted February 13 5 hours ago, John Carroll said: Are you saying the pipe marked "flow"is the hot supply to the mixer?, thought that might be the manifold cold return to the boiler, if the flow is as shown then the Mot. valve is on the return?. Yes my motorised valve is on the return. Both of them are. I can't remember the reasoning but it works. Link to comment Share on other sites More sharing options...
nickldn Posted February 13 Author Share Posted February 13 I did some testing this morning and not much luck. The gauge continues to show the flow temperature from the boiler, no matter how the dial below it is set. Tomorrow I'll set the dial to minimum and set the flow temperature to 60 degrees. If the floor warms up a lot then I will know the blending valve doesn't work. Thank you for your help. I feel that I understand how this is supposed to work now. Link to comment Share on other sites More sharing options...
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