Underfloor heating issue in newly tiled bathroom

rangor gubbins

rangor gubbins

rangor gubbins

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Kent, UK
Hi,
I'm hoping someone has some ideas of what could be the problem with the UFH in our newly tiled shower room.
The shower room is heated by a wet UFH system, the same as the rest of the house. It's with an ASHP so has low flow temps (around 45 °C currently). The problem is that the new tiles are not getting very warm even after hours of the new loop running. All the other loops on the same manifold are working fine as they have been for years. The bit of exposed pipe for the new loop (flow and return) for the shower room is getting hot as expected but the heat doesn't seem to be coming through to the tiles.
What is weird is that the new loop runs through another little corridor which was tiled at the same time as the shower room but with different tiles, and the these tiles do get warm. Also the shower tray in the shower room gets warm, just not the tiles!
The tiles are just normal porcelain floor tiles from topps tiles, approved for UFH.
Anyone got any ideas what could be the problem? The builders are back in tomorrow and I want to discuss with them what can be done.

Under the tiles and adhesive is 50-60 mm screed with the UFH loop in, below that is 25 mm PIR celotex, below that is sand, and then concrete.
It's a small room so it's not a long loop, around 14 m in length.
 
I think the tiles should be on insulated tile board, otherwise the heat will just be absorbed by the substrate. What was the screed laid onto? There must be another substrate as you can't screed onto celotex?
 
Participant said:
I think the tiles should be on insulated tile board, otherwise the heat will just be absorbed by the substrate. What was the screed laid onto? There must be another substrate as you can't screed onto celotex?
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The celotex should throw the heat back up to be fair.

How long is it running for? How thick are the tiles?
 
What are the tiles made of. I think some types work well with underfloor heating and others take a bit longer to heat up
 
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Participant said:
I think the tiles should be on insulated tile board, otherwise the heat will just be absorbed by the substrate. What was the screed laid onto? There must be another substrate as you can't screed onto celotex?
Click to expand...
Why do you say you can't screed onto PIR insulation board?

I'll double check with the builders tomorrow but from memory the layers top to bottom:
Tiles
Adhesive (bal flexible)
~60 mm Cement screed with UFH pipes in
25 mm (or might be 50 mm) PIR insulation board
Membrane
Blinding sand
Concrete
 
50-60cm screed. So the low temp loops are having to heat a huge chunk of concrete before the tiles.

Need larger pipe and closer spacing probably.
 
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200sols said:
50-60cm screed. So the low temp loops are having to heat a huge chunk of concrete before the tiles.

Need larger pipe and closer spacing probably.
Click to expand...
Could be that, maybe I just need to leave it running longer for the screed and tiles to warm up. The pipes are 22mm diameter though and the loops are spaced same as in the rest of the house.
 
In our kitchen, the same thickness screed with thick terracota tiles only takes about 1-2 hours to feel nice and warm. There is 100 mm PIR insulation below that though, rather than only 25 mm in the shower room.
 
Yup screed ontop of celotex is do able,no problem with this
Pipes may be connected wrong to manifold maybe or possibly a blockage in the uf pipes?
 
henry hoov3r said:
Can you post a picture of the manifold. Also a picture of the zone thats not working.
Click to expand...
Manifold - the new loop is the first one on the left. The one with the nice clean flow setter!



Short pipe run from manifold through first door, then to next doorway of the bathroom.

Top down view of pipe run from manifold to bathroom



The loops in the bathroom. 200 mm spacings, the pipes are 22 mm diam., theres 25mm PIR insulation under the pipes.



Bathroom floor tiled, with red circles around where I can feel the tiles warming up after several hours of running the pipes
 
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rangor gubbins said:
Manifold - the new loop is the first one on the left. The one with the nice clean flow setter!




Short pipe run from manifold to the doorway of the bathroom.
Click to expand...

Might be worth unscrewing the thermostat head on the zone that’s labeled bath. Im assuming that’s the zone thats not working properly. Just unscrew it and take it completely off.
 
That loop is the least efficient way to run UFH. Snail shell pattern means a good even spread of heat. This sort of snake pattern means that you are grouping lots of heat together, not spreading it out.
 
henry hoov3r said:
Might be worth unscrewing the thermostat head on the zone that’s labeled bath. Im assuming that’s the zone thats not working properly. Just unscrew it and take it completely off.
Click to expand...
We've tried that. The thermostat head has been off all day today and still the tiles are still only just getting warm in the areas marked in red on the above photo.
 
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