magnaclean filter and low loss header

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I give up, we're going round in circles. :rolleyes:

You may be, I'm not.
I've just given the reasons behind the reverse return and the LLH.
Sorry if you don't like it.

Nothing you said Onetap :oops:

I welcome your opinion, although I don't agree which is quite obvious, from my posts before you.

I won't be changing my mind ;)

Been reading the MI on some of the Keston, and I'm pretty sure they wouldn't approve the two boiler, reverse return system.

Perhaps if I'm bored tomorrow I'll send them an e.
 
Been reading the MI on some of the Keston, and I'm pretty sure they wouldn't approve the two boiler, reverse return system.

Perhaps if I'm bored tomorrow I'll send them an e.

I think they might approve it. ;)

http://www.keston.co.uk/downloads/support_info/multiple/2xcelsius-v2.pdf[/QUOTE]

Oh dear whats that ABV doing there. :rolleyes: I see they recommend a 35mm header, whereas I suggested 42mm.

The rest is just about spot on to what I've spent the last 7 pages saying.


 
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Oh dear whats that ABV doing there.

Since it's not a LLH system, it is intended to maintain the flow through the boiler if the TRVs are shut. I've no issues with the ABV, you just don't need it with the LLh arrangement.
 
That confused me.

The OP hasn't got an LLH.

He hasn't got a by-pass on the 3 port valve.

The open circuit is reducing the system flow.

Why would Keston show an ABV in a reverse return header if they didn't think it was necessary.

Why have we spent about 14-15 pages over two threads if there's nothing wrong with the installation.

Perhaps you haven't seen the pic on page 1.

Note the fully open gate valve.
 
Should I consider getting a magnaclean filter installed on my fragile dual Keston Celsius 25 system? If so, where? As it is primarily to protect the boilers, my initial thought is it should be in the low-loss header between the primary return and the boilers, maybe on the far right of the picture, next to the gas meter, so it is immediately before the boiler returns.
 
I don't understand why there is a 3-port valve for a single zone CH and DHW when there is a 2-port valve on the DHW by the cylinder, unless it's left over from the previous installation (single 25kW non-condensing with vented indirect DHW).

Yes.

A 2-port zone valve comes with the unvented cylinder and must be fitted, since it is a safety device.

The vented system was probably a Y-plan ( one mid-position 3-port valve). The installer of the unvented cylinder re-used the existing 3-port valve, to avoid spending more money; a bodge IMHO.

The preferred method is to buy a second 2-port valve and convert the system to S-plan.
 
Oh dear whats that ABV doing there.

Since it's not a LLH system, it is intended to maintain the flow through the boiler if the TRVs are shut. I've no issues with the ABV, you just don't need it with the LLh arrangement.

Ok, I'll rephrase the question.

What happens if you replace the ABV with a fully open gate valve as in the OP's pic.
 
What happens if you replace the ABV with a fully open gate valve as in the OP's pic.
I think there will be very little (no) flow through the radiators as 99% of the boiler flow would go through the short circuit gate valve. Isn't that what happens with a LLH if there is no secondary circulation pump?

Interesting Keston info from OneTap. I'd wondered about a check valve on each boiler to prevent back flow through an idle boiler. In their schematic, they are using the boiler pumps for radiator circulation and an idle boiler without a CV would be a short-circuit for the active boiler. It looks like the primary circuit should be 35mm instead of 28mm. So doitall suggests 42mm, fair play.

I've googled 'reverse return piping' and now see how it relates to my installation; it keeps the pipe lengths to each boiler the same length. Referring back to the Keston schematic, the reverse return piping looks like it is there to balance the flow through the boilers and the ABV is there to ensure adequate flow through the boilers. An ABV should prevent the individual pumps from stalling as it should be set below the stalling head of either pump at minimum speed. As the pumps modulate down in speed, the ABV will become more restrictive, maintaining delta-T across the boilers (something a LLH won't do unless you put an ABV in each boiler flow).

With a proper LLH, I assume each boiler would be plumbed separately into the big LLH and the boiler pipe lengths wouldn't need to match. I seem to have two boilers on a reverse return scheme but with an open by-pass and no check valve on each boiler. With the gate valve wide open, it has some of the characteristics of a LLH but 28mm is too small to be considered low-loss. If the primary circuit was replaced with 35mm (or 42mm) and the gate valve was replaced with open pipe, it would be closer to a LLH system.

What I have is neither the Keston reverse return scheme (missing check valves and ABV) nor is it a LLH (too small). By keeping the gate valve open, it shares some characteristics of a LLH. My temperature measurement chart suggests the flow through the boilers is more than adequate (maximum boiler delta-T of 15°C). Replacing the open gate valve with an ABV should reduce the flow and increase the pressure drop and delta-T (20°C) between boiler flow and return, yet the modulating pumps would cope. Leaving the gate valve open means the pressure drop between flow and return is less than with an ABV, so the modulating pumps should still cope.

Partially closing the gate valve (as it was) risks stalling one of the boiler pumps and damaging a HX.

If I want the system to run efficiently (condensing), I should follow the Keston schematic; check valves, ABV and bigger circuit up to ABV. What they don't show is the secondary circulation pump; I'd want to keep it after the primary circuit ABV to cope with the undersized 28mm secondary pipework. After all that, I suspect condensing savings would be minimal as I am stuck with a flow temperature for DHW. (To maximise condensing savings, I'd need a boiler return temperature of 30°C.)
 
My temperature measurement chart suggests the flow through the boilers is more than adequate (maximum boiler delta-T of 15°C).

That is not a happy coincidence, it is the boiler controls (primary side) working as they are meant to. The controls will modulate the burner to deliver the set flow temperature (as set by the knob on the boiler?) AND will also alter the pumps' speeds to maintain the dT across the boiler at 15 degC, or as close as practical.

The pumps are not variable speed; they are 3-speed types, but the boiler controller alters the speed setting.

It looks like the primary circuit should be 35mm instead of 28mm. So doitall suggests 42mm, fair play.

We're all agreed (you, Doitall, Keston, me) that the 28mm should have been larger. GT/Drivel also would have it larger, to the point where it ceased being a pipe and became a storage vessel.

However, that is not the major problem with this system. Given that it runs with just one boiler for most of the time, it is a secondary problem. It will work with a 28mm LLH. If you were to make alterations to the pipework, I'd change it, but not until you've solved the major problems.

The major problem is that there seems to be no controller on the secondary side. The existing controller is the user adjusting the boiler flow temperature knobs and switching 1 or 2 boilers on, as required.

The boiler system has been added to a Y-plan system, that was later hacked into a S-plan. Both of these are on/off thermostat controlled systems and are incapable of altering the flow temperature to achieve the maximum efficiency from a modulating condensing boiler. You need a variable/low flow temperature for the space heating and you need a high flow temperature occasionally when there is a DHW demand.

Also, the secondary pump may be undersized (to deal with the output from two boilers running) and the CH control valve needs sorting.
 
When the HX goes again come back and ask the question a third time.

In the meantime the,

Header is undersized for the boilers.

The system primaries are undersized.

The ABV is missing allowing a short circuit and possibly stall the boiler pumps on low speed.

The 3 port valve needs a bypass, unless it's port A to the cylinder.

Happy 2011.

Ps, send the problem to Keston and see what they have to say.
 
I am almost happy that the system is just about OK as it is. If I thought the boilers would last another 10 years, I might get the boiler pipework brought up to spec. In the meantime, I was thinking of a magnetic filter and Sentinel X400 flush to nurse things along.

There are also issues with the condensate drain; twin 22mm external with internal spec insulation into a soak away in chalk bedrock close to foundations. One saving grace is that the condensate runs down a south-facing wall, which may have saved it from freezing (although the insulation is crumbling in the sun).

If one boiler fails, I'd replace both with a 32-36kW 4-pipe system boiler with weather compensation and run the condensate internally then buried into a new limestone chip filled soak away, probably under the drive.

Anyway, thanks guys and have a great 2011.
 
In my opinion the system isn't ok as it is, and fitting a filter will make it worse, and even more so if you fit one on each boiler.

The only possible position for the filter would be in the common return to the left of the boiler.

As you have agreed, you are already loosing 50% of the boiler output to the open circuit.

Were you to fit a flow meter in the header return, you would see exactly what I'm talking about.

When you change the boilers, you will need to get rid of the 3port valve, and upgrade the pipework anyway, so why not do it now and the existing boilers will last twice as long, and be more efficient.
 
The reason I am losing 50% of the boiler flow is because the header gate valve (by-pass) is doing its job and reducing the harmful 30°C delta-T from the cold radiators down to 15°C across the boilers.

When cycling on the room thermostats all the TRVs are near their set points; reducing radiator flow and increasing delta-T. From my chart, this delta-T was 17°C and would be almost perfect for the boilers. Unfortunately, there is still excess flow in the header, so the delta-T across the boilers is only 10°C. I put this down to the open gate valve rather than an ABV.

The flow through the radiators is fixed by their balance and not by the boiler. I accept that the two boilers are too big, but one of them alone is not enough to match the radiator output. I'm not too bothered about that as boilers seem to be more efficient at part load.

I don't know if the 2-port valve on the HWC is only controlled by the fixed (safety?) thermostat near the top of the cylinder.
 

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