Is this Low Loss Header suitable?

[windsor-tg]

I am looking to replace my existing Vaillant heat-only boiler with a new Vaillant ecotec plus 630 system boiler (30kW). I have a megaflo hot-water cylinder, a central heating system (serving 21 radiators) and an orangery built last year (6m x 4m) with underfloor heating. Through running some tests, it has been found that the heat exchanger on my existing boiler is partially blocked.

The issue I have am currently having is that whenever I turn on the UFH only, the boiler, after about 60-70 mins of running, will start continually anti-cycling (modulating) even though the heat demand is enough to warrant continuous firing of the boiler. This has boiled down to the fact that the heat demand to the boiler (when only the UFH is on) is less than the minimum the boiler can deliver.To get around this, I need to turn on the CH so that the boiler will continuously fire and the UFH will remain on.

Having had a few heating engineers come over to assess the issue, the general consensus/recommendation is for a new system boiler to be installed along with a Low Loss Header (LLH). The installer I have in mind to install the new system is recommending the FlexEJ 3/4" DN20 LP 30kW LLH. Does anyone have positive/negative views about this LLH, and whether one flow and return on the secondary side is sufficient? Is there an alternative LLH that may be more suitable?

 

[oz-plumber]

From my understanding - and I stand to be corrected, you would need 3 pairs of ports on the secondary side.
1 for each of your requirements.

• Cylinder
• Radiators
• UFH.

And 3 pumps on secondary side ( unless you have a pump at the UFH manifold - then 2 pumps )

You could use the LLH as specified, but you would be basically setting up the system on the secondary side of the LLH the same as you would of you had a 3 pair LLH.

See if the company can make a LLH with 3 sets of ports on the secondary side.

 

[windsor-tg]

thanks @oz-plumber.

I have an UFH pump on the manifold so I am assuming I can use my existing 25-80 pump on the secondary for the CH & HW, and the existing UFH manifold pump. The new system boiler comes with its own internal pump.

I have been watching the Tomkat video (

) which shows that only one flow & return on the secondary side is needed. I have attached a photo I took from the video that shows this. The video also goes onto say that the pumps go onto the secondary flow becasuse it puts the system under positive pressure.

There is also this article on Heat Geek (Low Loss Headers: The Complete Guide For Efficient Design - https://www.heatgeek.com/low-loss-headers/) under the section 'Do not use Multiple Tappings' which recommends not to install a LLH with multiple outlets on the secondary side. This can result in some circuits being hotter than others.

I think the 1" LLH may be more appropriate DN25 (1″) FlexEJ LP Low Loss Header 50 kW | 24hr Shipping | FlexEJ Direct - https://www.flexej.co.uk/shop/low-loss-headers/lp-low-loss-headers/dn25-1-flexej-low-loss-header-50-kw/