Underfloor heating manifold how it works?

[Martysmarty]

Hi all.

 

Now i know i may be asking a daft question but here goes.

 

I have got a single zone ufh manifold in my kitchen that i have got to comission. Its a reliance unit, rads all other rooms, on a combi boiler

 

Now this mixer, does the flow from the boiler into the ufh loop ever shut off before the room stat? I see it has to maintain a much lower temperature on the wax stat thats built into the manifold.

 

My concern is by running underfloor heating without the radiator zone active,  the wax stat in in the manifold will shut off intermittently to regulate the input temperature from the flow.

 

Or, does the manifold never turn off, but rather constantly run but at a reduced flow from the boiler, and mix in the cooler water thats in the loops?

 

A bypass valve is there if anything went wrong as such, and once the room is up to temp i know it will turn it all off anyway. Its initial warmup im thinking

 

The rads and ufh are seperated using two port valves and two room stats. 

 

 

[Temp]

During start up the mixer is most likely wide open as the return will be cold. It will start to close as the floor reaches the set temperature.  Its most likely to close if you wait until the floor is hot then turn the mixer temperature down. In that condition the return temperature might be hotter than the set temperature.

 

I don't think they fully close as some manifolds have an over temperature sensor that turns off the loop pump to protect certain types of floor covering and feet.

[Temp]

Might be worth posting a picture of the manifold. Some types have a built in bypass.

[Martysmarty]

I will get a picture up if needed, but its a grunfos pump with a reliance mixer, model UFHC980357

 

Its got a probe on the flow to switch the pump on

 

if it dont fully close then were all good, should it close then the auto bypass thats already on my boiler will loop the circuit, correct me if im wrong but the boiler will detect minimal to no temp loss from the flow and return and just turn off anyway?

 

Just trying to get my head around it.

 

Thanks for your reply. 

[Temp]

18 hours ago, Martysmarty said:

UFHC980357

 

The pdf here has a graph which suggests the boiler return can indeed be reduced to zero..

 

https://www.underfloorshop.co.uk/wp-content/uploads/2017/01/Reliance-Single-Room-Pump-Pack.pdf

 

Edit: sorry that a 352 not a 357.

Edited July 17, 2021 by Temp

[Temp]

This for the 357 says same..

 

https://underfloorheatingsupply.co.uk/wp-content/uploads/2020/07/Single-room-underfloor-heating-control.pdf

 

[Martysmarty]

Thank you Temp for picking up on that, i will have a read.

 

I was hoping it wouldnt but all should be ok with thd bypass valve but i guess we will see.

[Nickfromwales]

Do you plan to routinely run the single UFH loop off the boiler, independently?

[Martysmarty]

Cant say as i do, mostly its for commissioning and future maintenance really. 

 

Generally though theres not a lot of need, and if at all i think it would be the other way around.

[Nickfromwales]

3 hours ago, Martysmarty said:

Cant say as i do, mostly its for commissioning and future maintenance really. 

 

Generally though theres not a lot of need, and if at all i think it would be the other way around.

If you can only have the UFH on when the rads are on, it would help massively. If not, you’ll need a buffer tank for sure. 

[Martysmarty]

Hi nick, so a bypass valve alone wouldnt cut it?

[Nickfromwales]

13 hours ago, Martysmarty said:

Hi nick, so a bypass valve alone wouldnt cut it?

Not on a boiler > single loop UFH setup. Deffo not a healthy arrangement for the boiler. The manufacturers installation guides often state that short cycling should be mitigated against by design. You need a 50L buffer in series with the flow, between the zone valve and the UFH manifold, and a 22mm gate valve ( NOT a bypass valve ) fitted across the flow and return connections where they supply the manifold.

I use the 50L version and works a treat. These are very well insulated and wall mounted.

Just connect the boiler flow ( after the ZV ) to one upper tapping, and and then UFH flow to the diagonally opposite lower tapping. Blank the two other tappings off. That will give you sufficient energy buffering to not have the boiler ever running under duress.

[Martysmarty]

Hi nick

 

Iv had a good think about this, and thankyou for the info on  setting up a tank. the problem i have is i really dont have the space to put it 

 

I am now thinking of just keeping it simple and keeping the radiators 'always on' without a valve. And just use a 2 port valve on the ufh so i can run two stats.

 

I have a rad without a trv on it so it would save the messing around. It was my original plan.

 

What do you think?

[Nickfromwales]

You can fit 2x 25L tanks also. 
Having one rad on bypass ( no TRV and open lock shield ) will give about 5-7L of additional system volume, and you may get away with that. Hopefully that would be the absolute worst case and if you’re using heating, hopefully a couple of other rads would be at least allowing a trickle through partially closed TRV’s elsewhere on the system. 

Go for it, but try to keep an eye on the boiler cycling to see how it performs. 

Edited July 22, 2021 by Nickfromwales

[Martysmarty]

Just reporting back to this. I set it up. Using a rad without a trv and all up and running. Got it increasing heat slowly.

 

Thank you for all your help, hopefully no issues.