Advice needed. Issues with underfloor heating and hot water system for new build

[Nostrum]

My understanding is the UFH pumps only circulate the blended water in the circuits, there is a clear path through from flow to return and the UFH only takes primary flow water to make up the lost heat in the circuit. The flow and return to manifold will need balancing to 20 degree differential once the whole system can be run.

as it is they are probably not balanced and the return temp is being prematurely raised which will cause the boiler to cycle.

The hw is not working due to a very low resistance circuit (much lower than cylinder circuit) maybe as described above, or if what carrera is saying is true, reverse circulation through the cylinder.

the magna is the main pump and when you consider what it's doing, should be man enough. The Pipework should be up to the job if I understand the design.

My advise would be to tee in the hot water return independently to ensure it's not reverse circulating, double check everything in that circuit and the Pipework for blockage.

the boiler connections are 28mm and the internals are probably 22mm, it's the overall resistance not one small section of pipe that will probably be negligible.

 

[Carrera]

Looks to me 6 manifolds 3flows 3 returns and flow return to rad circuit

Do you have the sheet with the calcs for the underfloor Spec manifold sizes pipe length ect

Yes , you might be able to get one more with a bit of fiddling

You would end up with 3 manifolds on one circuit, and 3 independent manifolds, so four feeds

 

[Gray0689]

Yes , you might be able to get one more with a bit of fiddling

You would end up with 3 manifolds on one circuit, and 3 independent manifolds, so four feeds

What size are the manifolds on the one line of 28mm flow
How many ports on manifolds

 

[Gray0689]

My understanding is the UFH pumps only circulate the blended water in the circuits, there is a clear path through from flow to return and the UFH only takes primary flow water to make up the lost heat in the circuit. The flow and return to manifold will need balancing to 20 degree differential once the whole system can be run.

as it is they are probably not balanced and the return temp is being prematurely raised which will cause the boiler to cycle.

The hw is not working due to a very low resistance circuit (much lower than cylinder circuit) maybe as described above, or if what carrera is saying is true, reverse circulation through the cylinder.

the magna is the main pump and when you consider what it's doing, should be man enough. The Pipework should be up to the job if I understand the design.

My advise would be to tee in the hot water return independently to ensure it's not reverse circulating, double check everything in that circuit and the Pipework for blockage.

the boiler connections are 28mm and the internals are probably 22mm, it's the overall resistance not one small section of pipe that will probably be negligible.

The blended water will be the full flow if the boiler can't heat the demand on the heating
6 manifolds 6 pumps going on a flow out of boiler at 28mm don't matter if some of pipework is 35mm won't get the flow rate out it needs that's my opinion anyway

 

[Nostrum]

So your telling me that Pipework won't be able to cope with 6k of heat (min output fully modulated approx)?

Of course it will. But not if it's coming back at almost full temperature, it'll cycle.

the problem is to much flow, not to little.

 

[Nostrum]

I take that back as I have read the O.P wrong...

 

[Nostrum]

So when the heating only is running carrera, is the heating working effectively?

You haven't mentioned any problems with it, just the hot water?

 

[Nostrum]

Manifold temp is a constant 41 degrees, is that what it is set to?

 

[solutions]

View attachment 16396
Don it albeit sideways!
this is the plant room setup

 

[Ermintrude]

Build a nice LLH and set pumps up for ufh with a pipe stat on return to manifolds (floor side) controlling pumps on and off. I always build in a two port on flow but that's down to you.
Towel Warner's on own pump with prog stat.
DHW on its own with a two port and a balancing valve

I would in hindsight install balancing valves and a Venturi plate on each return to allow the system to be balanced properly as currently the washing up in a student house if 8 lads looks easier to balance .

LLH should have a decent internal volume to buffer the system or install an thermal store which with a few take offs and this will act as your LLH. ACV do one. But that's about £2k.

The ACV SLME is the jobbie.