Unable to run bath of hot water after boiler change

[John.g]

Practically speaking, that sounds truly incredible, most gas boilers will only go into recycle or perhaps modulate down if the dT exceeds say 30C.
Surprising (or maybe not) that the Viessmann guys didn't reveal this.
I would ask them straight out the facts of the above.

 

[ShaunCorbs]

No it’s installed correctly … 28mm to 2 manifolds upstairs (flow & return) and 2 manifolds downstairs… no temperature control, but balanced flow. Each zone is temperature controlled by individual digital room stats.

There is no issue with heating, been working find since install.

But no thermostatic overheat protection / temp blending

 

[sargan]

But no thermostatic overheat protection / temp blending

Correct it was not part of the Nu-Heat system, they did design & supplied the kit, it relied on the Thermal Store stat controlling temp.
I do intend adding a Thermostatic mixing valve, I have posted a Q on it today …. welcome any comments if you take a read.

Adding Thermostatic Mixing Valve - UK Plumbers Forums | Plumbing Advice; Plumbers Talk Forum

I have NuHeat UFH system, and this has no Thermostatic Blending valve on the heating circuit. (Heat Master II cylinder has pick up coil) Nu-Heat System installed - This means I can't run store above 60C due to risk of overheating UFH pipes. I want to add a Thermostatic Mixing valve so...

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But no thermostatic overheat protection / temp blending

 

[ShaunCorbs]

What’s the floor construction/ covering ?

 

[sargan]

Ground floor 75mm reinforced on 1000mm insulation, screed over pipes, tiled finish mainly. Engineered wood floor on 2 rooms.
1st floor pipes clipped direct to underside of Wheyrock deck, then over covered with reflective foil & insulation. Floor covering tiled floors or laminate flooring.

Floor construction and finishes were all factored into Nu-Heat design.

 

[ShaunCorbs]

Can we see the manifold ?

 

[sargan]

Here is 1st floor manifold

 

[ShaunCorbs]

And the tiled floor is exactly the same as that ?

 

[sargan]

And the tiled floor is exactly the same as that ?

That is manifold fo4 all rooms on 1st floor.
Alupex F&R from manifold to each room, dual loops of apex pipes as the actual heating pipes.