Under Floor Heating Temperature

[DJJJEF]

Hi all.

I have a recent renovation install of an ufh systems in my downstairs, with rads & towel rails upstairs.

My boiler is a Worcester Bosch Greenstar 30kw system boiler connected also to a hot water tank. The boiler has a self regulating valve to reduce the heat flow temp when required.

I have had issues with my UFH from the very start with regard to floor temp.
My system was designed by Wunda, supplied as the full kit and fitted by a plumber who installs a Wunda system on the trade side at least once per month.

My issue has reached a point where Wunda are saying it’s a hot water flow volume problem that is overpowering the blending valve which cannot blend the heat down.

I have 5 loops. 3 in a large kitchen diner, circa 118m linear each. A hallway which is linear 55m, and a sitting room of 90m.
There was some question marks over the 100+m loops but Wunda are happy that is fine, even though the flow rates do not meet their guide of 3.0.

My main problem has been when the wider system closes off and leaves just the hallway running. The temp on the flow rises to 55/60deg with the blending valve set to minimum. As a result, the floor is reaching 30+ degrees quickly and shutting off.

I have LVT so it’s been freaking me out with these crazy spikes.

Wunda sent me a new blending valve which made no difference. We also checked the return to make sure there was no kinks in the plastic section of pipe, by running a new pipe free flow up the stairs and connected, behaviour was the same.

I have a bypass in the loft which is doing its job when needed.

The bar pressure at the manifold is 1.8bar so all good. I have also added a second bypass at the manifold.

No air, that’s been checked and run through well, system is very quiet.

The only way I can get the system to behave well is by bringing all 5 loops together on the controller so the volume can spread better, however I’ve lost room control and control of the floor probes in two areas.

Wunda are saying it’s because my boiler is pushing to much water and the blending valve/manifold cannot deal with it.

Their recommendation at the moment is to add further restriction before the ufh to help. However there is concern on that where the long loops may then get even less flow leaving the far ends colder than they should be.

They did say to reduce the boiler flow but I can only go down to just north of 60deg where it’s feeding the hot water tank.

It’s all in 22mm pipe. Pump is a Will Para which I have tried on variable and constant. Power 2 & 3z
I think I have covered most of the setup to help paint the picture.


So my question is; does this sound like what they say? The boiler is too powerful when just serving the Ufh if runs are short and not enough cold is returning to cool the flow temp?
If the hot water was being circulated, and or the upstairs heating was on, they say it would be fine. Could it be a blending valve not up the the task?


It appears right now that if they are correct, I need to either restrict the flow somehow whilst not effecting upstairs heating and hot water. or maybe there is a blending valve that can handle the volume with a lower mixing temp? My valve I think runs at 30deg on minimum (when not being over powered), would a valve that can go down to 20 or 25deg help?


Thanks in advance for any advice or comments.

 

[dilalio]

The boiler has a self regulating valve

What is this?
Not sure what you're referring to here!

 

[DJJJEF]

Sorry, probably wrong terminology. Plumber told me, I may have misunderstood him a bit.
The boiler reduces if the demand from the system drops, I.e if some rads switched off. I think that’s what it does. The app flame drops from full (red) to a smaller flame (orange).

 

[dilalio]

Sorry, probably wrong terminology. Plumber told me, I may have misunderstood him a bit.
The boiler reduces if the demand from the system drops, I.e if some rads switched off. I think that’s what it does. The app flame drops from full (red) to a smaller flame (orange).

Modulation.

 

[dilalio]

Is flow and return the correct way round, going into the blending valve?

 

[dilalio]

What's the GC number of your greenstar?

If it's a modern one, it should have a turndown ratio of 10:1, meaning that it can modulate down to 10% of its maximum output so - 30kW to 3kW.

If your ufh heatloss is lower than this, the boiler will cycle on and off.

But! The blending valve should still mix flow and return to achieve the desired temperature required by the loops.

So, check flow and return as the 1st step.

 

[DJJJEF]

Modulating valve, that’s it

Yes, the flow pipe is coming down and about 55deg on the copper before it enters the blending pipes and going into the hot side of the valve. It follows the arrows on the fittings.

 

[DJJJEF]

It’s a Greenstar 4000, 30kw. System boiler condensing. Installed around 2 years ago so new yes.

Just another thing, flow and return are always bang on, 7deg drop.
So on all loops, a drop of around 7, and on the full manifold, a drop of around 7 from the flow gauge to the return gauge.
Even when the water flies up to 55deg, the return is then 48deg.

 

[dilalio]

Modulating valve, that’s it

It's not a valve.
It's the fan speed and burner which "modulate" - basically like your foot up and down on a car accelerator pedal, or turning a gas hob dial up and down.

 

[dilalio]

Modulating valve, that’s it

Yes, the flow pipe is coming down and about 55deg on the copper before it enters the blending pipes and going into the hot side of the valve. It follows the arrows on the fittings.

OK but is the flow pipe going into the correct port on the blending valve?

55° is not out of the park for UFH flow temp.

What is the target floor temp for your LVT? What can it withstand?

How and where are you measuring temperatures?

 

[DJJJEF]

The blending valve is on minimum, cranked as far closed as possible. When all loops are running, it’s 30deg, when just one, it flies up to 55deg when the boiler is at 65deg flow, if I have the boiler it jumps even more.

When all loops are open and it’s running, 30deg flow is ok, return about 23deg.

I have LVT which is a max of 27deg.

Each zone has a stat with a wired probe sitting at the very top of the SLC I put under, Mapei Ultra Renovation Screed. The probe is kicking in and turning the system off when it hits 27.

Another problem with Wunda…..

The stats are wireless to the controller and app, with a wired probe. The stats seem to only pole every 10 mins. According to Wunda it’s every minute but I am watching these temps via the app like a hawk. I have had a temp of 25, 10 mins later it’s 28.5. So it’s not getting the temp frequently enough for my liking. The be ended up having to set the probes to 25 to allow for the time lag between polling. Maybe it would be more frequent on wired stats, but with wireless L, possibly piling that frequent would eat the batteries?

 

[dilalio]

OK, so, just to confirm...
The only loop with issues is the hallway one, when all other circuits are satisfied?

 

[DJJJEF]

Thats the biggest issue yes.
The larger zone made of 3 loops is big enough to have return water cool the flow. But just the 55m loop sends the temp to over 55, and the other loop jumps to around 40/45. So the smaller two are both a issue but the small one more so.

I was hoping a more robust blending valve may help, one which can blend down lower. I had concerns over reducing the flow into the system for the sake of the flow meters not getting to where they need to.

I set the pump to speed 1 as a test and the flow was to low, early part of the loop was really hot, second half was cold. So I need enough power to service around 500 linear meters of 16mm pipe when all is on.

 

[dilalio]

Thats the biggest issue yes.
The larger zone made of 3 loops is big enough to have return water cool the flow. But just the 55m loop sends the temp to over 55, and the other loop jumps to around 40/45. So the smaller two are both a issue but the small one more so.

I was hoping a more robust blending valve may help, one which can blend down lower. I had concerns over reducing the flow into the system for the sake of the flow meters not getting to where they need to.

I set the pump to speed 1 as a test and the flow was to low, early part of the loop was really hot, second half was cold. So I need enough power to service around 500 linear meters of 16mm pipe when all is on.

Well, if all but the smallest zones are off, and the mixing valve works as it should during open zone demand, then the mixing valve may, as wunda have said, become overwhelmed!

The boiler pump should also modulate to decrease the flow rate and not over stress the mixer.

Do you have any data/graphs for the mixer? And also the system pump?

Speak to their tech depts.

 

[DJJJEF]

Yeah it does seem that is the issue. It’s a pain because the hallway, being a cold zone compared to other rooms due to stairs and front door, does tend to be on when others are at temp.

Thanks for your input.