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- 15 Nov 2026
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Hi All,
Looking for some advice on my UFH that's never worked particularly efficiently since installation (taking hours to get warm and sometimes never reaching thermostat temp on cold days).
It was installed brand new during a renovation 2 years ago.
I've been investigating it recently and have noticed some strange behaviour with the circulation pump and manifold.
System setup:
- Wet UFH with 4 loops, connected to the same boiler as the upstairs radiators.
- Wilo pump with thermostatic mixing valve.
- Flow meters on the upper manifold.
- Mixing valve currently set to 45°C.
- Pump recently changed to constant differential-pressure mode, setting 2, which has improved things.
Problems I've noticed:
1. Intermittent flow: When the boiler fires, the flow meters increase to around 1–2 L/min per loop, but gradually fall back to zero when the boiler stops firing. The Wilo pump remains powered throughout, and the thermostat is still demanding heat, but there is no flow once the boiler stops firing.
2. Pump settings: Increasing the pump power seems to reduce the flow rather than increase it. At higher settings, the flow meters drop to zero. Heating performance seemed to improve after switching to constant-pressure mode, but flow is still intermittent.
3. Mixing valve: When I increase the mixing valve temperature towards 60–65c, flow increases significantly and stays constant. Reducing it back to 45c seems to restrict circulation. I've left it at 45 rather than running it at an excessively high temperature (worried about my engineered wood floor).
4. Manifold temperatures - Reverse flow?. Starting from cold, the bottom bar heats up first, and is much hotter to touch than the the top bar. Eventually the top bar heats up to a similar heat as the bottom. My understanding is that it should be the other way around.
5. Radiator interaction: UFH seems particularly poor when the central heating is also supplying the radiators, as though the UFH is struggling to circulate independently of the boiler pump.
6. Pump direction: I've checked the directional arrow on the Wilo pump housing, and it points downwards, towards the lower manifold. Is this not the wrong way? Does this explain the issue.
Interestingly, despite all this, the floor does eventually get warm and the room reaches temperature. However, it has always been quite slow and inefficient, particularly in colder weather. Is it that the boiler is effectively pumping the water backwards through the manifold, hence the pattern of heating between the bars, and why the flow stops when the boiler stops firing.
Interested to get people's thoughts (there's only so much YouTube education I can absorb..!)
I was fobbed off by engineer I spoke to ("if the room is warming up, then I'd just leave it"), but I'm worried that this is causing unseen damage and potential future nightmare.
Thanks!
Looking for some advice on my UFH that's never worked particularly efficiently since installation (taking hours to get warm and sometimes never reaching thermostat temp on cold days).
It was installed brand new during a renovation 2 years ago.
I've been investigating it recently and have noticed some strange behaviour with the circulation pump and manifold.
System setup:
- Wet UFH with 4 loops, connected to the same boiler as the upstairs radiators.
- Wilo pump with thermostatic mixing valve.
- Flow meters on the upper manifold.
- Mixing valve currently set to 45°C.
- Pump recently changed to constant differential-pressure mode, setting 2, which has improved things.
Problems I've noticed:
1. Intermittent flow: When the boiler fires, the flow meters increase to around 1–2 L/min per loop, but gradually fall back to zero when the boiler stops firing. The Wilo pump remains powered throughout, and the thermostat is still demanding heat, but there is no flow once the boiler stops firing.
2. Pump settings: Increasing the pump power seems to reduce the flow rather than increase it. At higher settings, the flow meters drop to zero. Heating performance seemed to improve after switching to constant-pressure mode, but flow is still intermittent.
3. Mixing valve: When I increase the mixing valve temperature towards 60–65c, flow increases significantly and stays constant. Reducing it back to 45c seems to restrict circulation. I've left it at 45 rather than running it at an excessively high temperature (worried about my engineered wood floor).
4. Manifold temperatures - Reverse flow?. Starting from cold, the bottom bar heats up first, and is much hotter to touch than the the top bar. Eventually the top bar heats up to a similar heat as the bottom. My understanding is that it should be the other way around.
5. Radiator interaction: UFH seems particularly poor when the central heating is also supplying the radiators, as though the UFH is struggling to circulate independently of the boiler pump.
6. Pump direction: I've checked the directional arrow on the Wilo pump housing, and it points downwards, towards the lower manifold. Is this not the wrong way? Does this explain the issue.
Interestingly, despite all this, the floor does eventually get warm and the room reaches temperature. However, it has always been quite slow and inefficient, particularly in colder weather. Is it that the boiler is effectively pumping the water backwards through the manifold, hence the pattern of heating between the bars, and why the flow stops when the boiler stops firing.
Interested to get people's thoughts (there's only so much YouTube education I can absorb..!)
I was fobbed off by engineer I spoke to ("if the room is warming up, then I'd just leave it"), but I'm worried that this is causing unseen damage and potential future nightmare.
Thanks!
