Underfloor heating nightmare

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Hi,
I have never joined a forum like this but we are at our wits end with a problem with our underfloor heating which has been laid in a new kitchen extension and are hoping that someone might be able to help us.

We (stupidly) got one company to lay the wet underfloor heating pipes and supply the manifold, our builder to lay the concrete screed on top and another plumber to connect the whole system up. This has meant that they can all blame each other now there is a problem and we can't find a solution.

Basically, we want to lay an engineered wooden floor but the temperature of some areas of the room are too hot (up to 32degrees C in parts) and all the flooring suppliers say flooring can't be laid over 27degrees maximum screed temperature. The manifold has a thermostat on it, the minimum temperature setting is 35degrees and this is giving us a screed temperature of up to 32degrees. The pipework was laid in three separate loops that come back to the manifold (although the manifold doesn't have any actuators) as it is effectively one zone as it is all in the same room. Two of these loops are producing a temperature you would expect with the manifold set to minimum - about 23 degrees, but one side of the room which is one loop is much higher (between 28-32degrees). The area just next to the manifold is also much hotter - 32degrees C. We cannot fit a probe in the screed to limit the floor temperature to 27degrees as if we put this in the hot area, the cold parts of the room won't heat up at all due to the huge temperature difference. The company that laid the pipes and fitted the manifold are saying that firstly there is no problem as any wooden floor will be fine over 27 (I am assured this isn't true) and that the huge difference in floor temp across the room is due to an uneven or poorly mixed screed - we watched it being laid and it looked fine. They have adjusted the flow rates as much as they can on the manifold to try and cool the hot zone down but it didn't make any difference at all.

There are two valves fitted from the boiler to the manifold so that the radiators in the rest of the house and the ufh run separately. Apart from the manifold thermostat which isn't bringing down the water temp enough, is there any other way we can stop the boiler letting so much hot water get to the manifold - but in a way that won't stop the radiators heating up properly? At the moment if we turn the boiler down, the underfloor heating becomes cooler but of course so do the radiators!

Any help would be so hugely appreciated, we haven't been able to put a floor on the screed in the new kitchen for four months and we still haven't been able to find anyone that can fix this problem despite several visits from plumbers who all seemed to not understand the problem at all. When I try to find an impartial underfloor heating expert on the internet it is impossible to tell if they will know what they are talking about!

Thanks.
 
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Laying insulation on top of ufh is not a good idea!

What ufh kit is installed?
What size is the kitchen extension?

Does the manifold have flow meters?
Were the f&r temperatures checked on each loop?
Were the 3 loops equal in length?

If you have a short loop and the flows are set equal then that loop will increase the output.

Some companies decrease the pipe spacing (modified spacing) near external walls or windows to increase the output also.
 
Thank you both so much for your help. Here are two photos of the manifold and of the pipework before the screed was laid. Yes, we have been told that they laid extra pipes to compensate for skylights and large patio doors, it is the loop under the skylights that is too hot.

It does sound like a flow balancing problem but the man who laid the pipe work has been back (very begrudgingly) and says he has adjusted it to make the hot area cooler and the two cooler areas hotter, it hasn't helped at all! He adjusted the flow rates by adjusting the little water floats on the top of the manifold (sorry I can't remember the name for them) In this photo I have attached though, all the floats look to be at the same level so I don't know if he has done this properly.

I had another plumber round who said that we should be adjusting the three white plastic valves on the manifold like you would a radiator valve to control the flow, this did seem to work but when the underfloor heating man who laid the pipes came back when i complained it was too hot he opened all three of them back up again and said we should never touch these as they are the return. Is this right? I am sorry, I know its difficult to understand what I am talking about when I can't remember the correct terms for any of the parts!

How do I go about finding an expert that can come and look at the whole system including the boiler, that I can trust as everyone who has been has had a completely different opinion?!

The floor is 37metres squared.

Thanks
 
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For a start I would loose the silly 15 mm iso valves on the 15 mm poly pipe
 
Who is managing this project? Did you appoint the various parties?

From the two pictures it looks like a competent UFH install.

27c is the maximum temperatures the engineered wood can be by regulation, but you certainly wouldn't want it any warmer..

That does mean that the sub floor can be warmer. Indeed because of the thermal resistivity of timber it will need to be.

To overcome the thermal inertia of the floor and the resulting lack of responsiveness it should be run at low flow temps and for much longer than radiators. Are your expectations un realistic?

State of the art systems have constantly running pumps and the flow temperature varies according to demand.. these can be set with a maximum flow temoerature of 30c if the floor covering is conductive.

Engineered wood is a great insulator..requiring higher flow temps...

make sure the flooring installers user the right membrane between the screed and the timber... not to would be an expensive mistake!
 
opened all three of them back up again and said we should never touch these as they are the return. Is this right

Yes thats right.
The bottom manifold is for fitting actuaters. Not fitted in your case.
So the caps are screwed down which opens the valves.

The top manifold has flow adjustment via the black ring. It should lift up a small proportion and unlock.
Then revolve to adjust the flow.

To calculate the flow rate for each underfloor heating loop, take the loop length and divide by 40. Ie example, 100 m loop lenght/40 = 2.5 l/min of flow for the underfloor heating loop.

Maximum loop length is between 100m -120m.
Pipe spacing for engineered wood should be no greater than 150mm ideally.
So you should have about 260/M for 37sq/M.

Your installers may have fitted a short loop in there and just equalised the flows resulting in an overheating section.

It's a double meander layout in line with what Rehau recommends and does look like the high quality Rehau piping.

Your loops look to be spaced at 200mm centers.
I'd estimate the one in the middle of the floor to be about 40m long max.

So no more than 1L/min on that one.
 
or better still use the installation specifications from the manufacturers of the UFH to set the right flow rate..
 
or better still use the installation specifications from the manufacturers of the UFH to set the right flow rate..

When you don't know the loop lengths and can only guess better still is use a thermocouple on the f&r to acheive the desired temperature drop.
Usually, a maximum temperature drop of 5°C for domestic projects and a 7.5°C for commercial projects.

Some facts and figures for TECTONIC OAK FLOORING.
Floor Top Surface Temperature: Max in use 27°
Floor Underside Temperature: Max in use 40°
Heat Output Max. in use 75W/m2
Floor Uneveness Max. 3mm in 3m
Floor joists & Ply Substrate mc (if appicable) Max: 12%
Distance of hot water pipes below boards (in screed) Min: 30mm
Distance of hot water pipes below boards - Min: 3mm
Subfloor / Room temperature at time of installation: 15-24°
Subfloor ERH (equilibrium relative humidity) at time of installation: 40-65%RH
ARH (ambient relative humidity) at time of installation: 40-60%RH
Joist spacing (if applicable) Max 400mm
Edge Expansion joint Min: 12mm
Thermal conductivity of TECTONIC™ 20 mm:λ = 0.17 W/mK
Thermal conductivity of TECTONIC™ 15mm: λ = 0.17 W/mK
 

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