View on Low Loss Header for domestic property

[Zencap]

We are experiencing problems with our heating system which has become apparent after adding a single zone UFH to a large kitchen area.

When the UFH kicks in, the flow to the CH Rads cools off. When the UFH is not on the Rads (13 in total) all get hot (quite slowly downstairs.

UFH has own pump and CH pump is brand new 15/60 and made no difference. System was powerlfushed in last year and boiler is under a year old Viesmann-100w 26kw. When UFH was done, new piping was done to all 4 downstairs rads.

2 plumbers are stumped by the issue as set up should work. Proposals are

Change Flow and Return pipes (which are hidden in walls) from boiler to air cupboard to 28mm.

Install Low Loss Header - a destratification pump to a low loss header (LLH). Before the LLH run a 22mm f & r to the dhw cylinder. Downstream of the LLH install a primary pump to run the CH circuit and UFH.

Pressurise the system

what are peoples views on this - any other ideas?

concern on LLH is this over kill and cause issues long term?

pressurising system is risky given upstairs pipes are older and could cause issue.

help greatly received

thanks

 

[ShaunCorbs]

Is the ufh on it’s own zone eg direct from the boiler

 

[Zencap]

Is the ufh on it’s own zone eg direct from the boiler

Forgive my poor knowledge, but I think no, flow from boilers goes up to airing cupboard and S plan (I think) with UFH and Rad flows straight after pump but UFH is first drop on pipes down so seems to be take that route first when that is called, and starving CH rads of flow. Have tried restricting flow to UFH but doesn’t make material diff.

 

[exedon2]

Picture of set up in airing cupboard would be useful
13 rads in truth is a bit meaningless what's there output? You could find it out by measuring them and looking at a rad size list .
Also output of underfloor?

 

[John.g]

One might think that boiler flow rate should not be a problem with UFH as its normally only ~ 1/3rd of the UFH flow, a UFH heat demand of say 8kw might require a circ flow rate of ~ 15 LPM but the boiler circ pump portion of this might only be 3 to 5 LPM, hardy enough to trouble any boiler circ pump when combined with any existing rad demand., maybe new CH pump mode/setting problem or boiler output not big enough?

 

[Zencap]

One might think that boiler flow rate should not be a problem with UFH as its normally only ~ 1/3rd of the UFH flow, a UFH heat demand of say 8kw might require a circ flow rate of ~ 15 LPM but the boiler circ pump portion of this might only be 3 to 5 LPM, hardy enough to trouble any boiler circ pump when combined with any existing rad demand., maybe new CH pump mode/setting problem or boiler output not big enough?

Agree, the CH pump has been changed to a new one and same result. Boiler output considered high enough.
Logic is the flow return is not happening effectively - so either the return pipe is restricting flow somehow or inefficiently set, this proposal to replace with new 28mm minimum but also suggestion to add the low loss header - just seems excessive??

 

[John.g]

Any idea of the UFH demand or/and better still the boiler CH temp, the manifold flowrate from the flow meters and the manifold flow and return temps?. Is the new CH pump external to the boiler?.

 

[Zencap]

Any idea of the UFH demand or/and better still the boiler CH temp, the manifold flowrate from the flow meters and the manifold flow and return temps?. Is the new CH pump external to the boiler?.

The new CH is external in airing cupboard.

We found the differential temperature’s between the flow and return were so far apart that the boiler kept cycling when on service mode. When the boiler runs in its normal mode the boiler plateaus at 64 degrees on the flow and returns at 55 degrees.

indont have flow rates

.

 

[ShaunCorbs]

From the pump

rads
Ufh
Hot water ?

 

[Zencap]

Picture of set up in airing cupboard would be useful
13 rads in truth is a bit meaningless what's there output? You could find it out by measuring them and looking at a rad size list .
Also output of underfloor?

 

[Zencap]

From the pump

rads
Ufh
Hot water ?

Correct - closest to pump is UFH, rads and hot water at top

 

[ShaunCorbs]

You got a pic of your ufh manifold?

 

[John.g]

The new CH is external in airing cupboard.

We found the differential temperature’s between the flow and return were so far apart that the boiler kept cycling when on service mode. When the boiler runs in its normal mode the boiler plateaus at 64 degrees on the flow and returns at 55 degrees.

indont have flow rates

.View attachment 47057

When you say normal mode do you mean on rads only? and getting cycling/high temp diff on UFH only? what's service mode ?

If on UFH only then the the boiler should only cycle for two reasons, either the UFH heating demand is lower than the minimum boiler output or some boiler protection is switching it off on this unavoidable high temperature differential which hardly warrents a LLH, a ABV should do.

 

[Zencap]

You got a pic of your ufh manifold?

 

[ShaunCorbs]

Are the flow guages set correctly with the plans spec ?