Low Loss Header Help

[fezster]

My central heating has never quite worked properly since installation and the reason has been largely due to a large boiler and multiple heating zones. It's a Vaillant 438 and I have 3 zones - 2 heating and one HW. The advice has been to install a low loss header and I've finally decided to invest the funds to do so. Future plans may be to install 2 smaller boilers, if that makes any difference to the advice given.

I wanted to get advice from the pros on whether the below setup makes sense. Finding domestic installers with experiece of LLHs is difficult and I want to have some knowledge of what's entailed before I choose somebody, to avoid getting an inadequate installation which is what happened first time around.

From what I've learned reading every post I can on LLHs, I've come up with:

1. Primaries from boiler into LLH with a 15/60 pump.
2. Secondary circuit for heating split into 2 zone's via zone valves, running off of a 25-80 pump. (This required because of the large index circuit on both upstairs and downstairs zones).
3. Secondary circuit to DHW with a 15/60 pump.

Does that sound basically right? Or should all 3 zones be separated off of the LLH? I wanted to avoid having to buy a second 25-80 if I can.

In terms of the LLH itself, would something like the Worcester Bosch 7716192614 suffice? Is there anything I should be looking out for when choosing a LLH?

Thanks.

 

[ShaunCorbs]

What's wrong with your system atm ?

 

[fezster]

S53s are quite common. Usually only when first starting up. It's a big system with roughly 15-20 rads in each heating zone. Once it gets going it is usually fine - until the second heating zone suddenly opens and hits the hot heat exchanger with cold water. Then the s53 cycle begins.

I've got it working satisfactorily by timing the heating zones appropriately in the morning, but I often wonder into the garage randomly and see the boiler is on s53 again at varying times of the day. So I want to sort it out properly.

I have a large thread on diynot from 5 years ago. Not sure if I'm allowed to post a link to it.

 

[ShaunCorbs]

TBH your boilers undersized

15-20 rads hope is 28mm runs

Sounds like you need a commercial heating engy Esp with 35-40 rads

 

[Last Plumber]

Hi
Do you know what the output of each zone is?

 

[fezster]

Slight correction to my previous post, now that I have the figures in front of me:

• 24 rads in total - 13 downstairs, 11 upstairs.
• Radiators are intentionally oversized, totalling 45KW (153k BTU).
• Whole house heat loss was calculated at 39KW with extensions which were planned and now complete (but subsequently discovered the old solid walls in fact had cavities with no insulation, so in reality closer to 35KW).
• Index circuit is on the ground floor with a loss of 2.12m. The worst on the upstairs is only 1.09m. The loss through the motorized valve is 0.4m and the heat exchanger is 4.05m. Total loss is 6.57m. All at a temperature differential of 20 degrees (75 flow, 55 return). Calculation was done by me but subsequently confirmed and corrected slightly by a helpful forum member. The Grundfos 25-80 was chosen based on this and has allowed all rads to now get fully hot, which they were not previously.
• Pipework could probably have done with being larger, with the majority being 22mm, tails in 15mm, and primaries from boiler 28mm.
• Unvented cylinder is located next to the boiler in the garage and I believe is rated at 22KW. It's a Megaflo 250l.

I believe the trade-off on the boiler sizing is that it needs to be able to handle a single zone as well as all zones. This, I believe, is where the low loss header would help, allowing the boiler to operate independently of the heating zones and ensuring recommended flow rate through it.

 

[Last Plumber]

You are right about the Pipe size. Bit small really. Can the provisional section (before the split in zones) not be enlarged? Or is it not that simple?
If it were my house I would probably go for the Vaillant 46 kw with Vaillants own Header. Going off how I read what you say.

The 466 Boiler has its own shunt pump which will deal with the header then you can size the other pumps as necessary.
I haven't seen this obviously.
@ShaunCorbs mentioned a Commercial Engineer. You may be best getting one to come and discuss it with you.

 

[fezster]

The 28mm pipework is all within the garage so can easily be upgraded. Given the system is working (problems described above aside), am I right in saying that the pipe size alone will not solve the issues I have due to the zone arrangement?

Looking at the Spirotech LLH, I may have answered some of my own questions. I.e. that the individual zones do not need to come off of the LLH itself, they can be zoned after the secondary flow from the LLH. And also that the shunt pump only needs to overcome the losses in the boiler and the primary circuit - so in fact, I can do away with the 25-80 altogether and instead have smaller pumps on each zone and as the shunt pump.

At this moment, I don't want to change the boiler, as it is only 5 years old. I'm thinking (perhaps wrongly!) a LLH will solve my S53 issue as the boiler will always have adequate flow through it. I just need reassuring the heating will still work adequately once it is installed - the theory all makes sense, but you can't beat practical experience.

I have an engineer coming next week who says he has done commercial work - I just like to be knowledgeable enough to make a judgement that what is being proposed will work, having already spent money previously with people who weren't able to deliver on their promises.

 

[ShaunCorbs]

Isn't s53 too low of a return temp ?

 

[fezster]

Correct. Usually due to inadequate flow. This is despite there being an auto bypass. My understanding is that on a big system, you're always going to get a slow ramp up time, and the vaillant 438 is renowned for not modulating down fast enough. This is with the new pcb which reportedly fixed the issue, though it did help.

 

[Last Plumber]

Isn't s53 too low of a return temp ?

Waiting period for something along those lines.

 

[ShaunCorbs]

It's one of those situations it needs either doing right and costing x amount or not doing at all (eg don't go half arsed about it)

 

[king of pipes]

Heres one i did seven years ago now just serviced it and still going strong 15 rads in the main house 2 large fan convectors in a loft apartment 2 large towel rails, and 250litre unvented cylinder with secondary return installed in the corner of a large garage come workshop just to give you a idea how it works . cheers kop

 

[fezster]

Thanks, appreciate the picture, if just to see what I should be expecting as a finished job from an installer.

Would you mind sharing some details on the installation - what brand of LLH is it and why it was necessary in this installation? The pumps all seem to be domestic which I assume means they can be sized according to the requirements of the boiler and each individual zone (thus negating my need for a large pump such as the 25-80).

 

[Old Account]

Thanks, appreciate the picture, if just to see what I should be expecting as a finished job from an installer.

Would you mind sharing some details on the installation - what brand of LLH is it and why it was necessary in this installation? The pumps all seem to be domestic which I assume means they can be sized according to the requirements of the boiler and each individual zone (thus negating my need for a large pump such as the 25-80).

As @Last Plumber has mentioned earlier better off using the low loss header from vaillant. The pumps you require have to sized according to the installation of your property. As mentioned earlier it would be better if you hired a commercial heating engineer he would surely tell you what you require. If you want to do it right this time it's better to get a good engineer and you will not have any issues later on.

 

[king of pipes]

I made the header myself welded it up out of 3"pipe and screwed threads to suit the layout , it feeds two dwellings the main house and then a loft apartment each has its own programable room stat so each is controlled ,the unvented cylinder primarys come off the header which is controlled by the programmer in view the boiler is connected to the programmer for on and off times , a low loss header is easy way off connecting various circuits to a boiler and works very well and is economical to run . cheers kop

 

[Vee]

LLH is best. Either make your own or buy one. I run a 65kW Ecotec with a 42mm home made header. The shunt pump is in the boiler, but you can wire a 15-50/60 to the terminals for the boiler to control. Then the pipework of the header is 3x UFH circuits and 1xDHW all via Grundfos 25-80. But best to use a variable pump of the header for the circuits if you can afford. Wire the controls incorporating a relay or I think Vaillant may do an accessory for this.

 

[fezster]

Thanks very much all. Your responses have given me some confidence I'm going down the right route. Hopefully the installers coming next week are as knowledgeable as you are on this.

 

[fezster]

My Low Loss Header is being installed in a couple of weeks, but I wanted to validate some of my installers recommendations. He has recommended I use my DAB VA 65/130:

https://www.dabpumps.com/sites/default/files/2016-03/VA_VB_VD_TS_ENG.pdf

As the boiler shunt pump on the primary side of the header. This makes sense to me because it can overcome the boilers' hex resistance of 4.05m at 1.633 m3/hr, at max flow rate. This pump is being used because I already have it (it was specced by my original installer, and has not been used. My installer says it is perfect for driving my primary circuit, and helps keeps my costs down, so it's a win-win).

What I don't quite understand is what happens when the boiler modulates down. The flow rate required is less, so the secondary side flow will be less (using a variable pump to the radiators), but the primary pump is fixed speed, so flow rate on the primary will exceed the secondary flow rate. Does this mean the delta T at the boiler will be lower - and isn't that then inefficient?

The installer (he's commercial by the way) says that it'll just work, but was a bit vague on detail. I don't doubt him, as he has fitted many of these, but I would like to understand why. I know some of you guys are quite technical so was hoping somebody could explain.

 

[Vee]

Sounds fine. The pump has three speed settings and setting can be tailored to your setup. The delta T will not only depend on the pump but the flow temperatures set and the demand within the system. The impact of oversizing in this instance as it only concerns the primary circuit is minimal if any.