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Old January 12th 19, 06:00 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 13:08, Dave Plowman (News) wrote:
In article ,
tim... wrote:
Anyhow, at my current house it is 55 and works perfectly well


You must have rather oversized rads?


If they have been sized for the typical -3 outside temp, then they ought
to have loads of spare capacity with the current weather.


--
Cheers,

John.

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Old January 12th 19, 06:05 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 10:25, RJH wrote:
On 12/01/2019 07:30, John Rumm wrote:
On 12/01/2019 00:55, RJH wrote:
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

snip

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs
as cool as it thinks it can get away with and still be able to reach
the target set point temperature in a reasonable amount of time.
(the relationship is set by choosing a mapping curve that reflects
the rate of heat loss of the building).


I don't follow how that can work properly, as for most homes
different rooms will have a different 'curve'. Or does tweaking the
TRV compensate?


It seems to work well enough in practice. Each room also has a TRV,
and I have the place split into two zones; upstairs and downstairs, so
that will account for some variation.

It needs a little bit of experimentation to set the profile the first
time - basically waiting for colder days and seeing if the system
still heats the place comfortably and quickly enough. If it doesn't,
then you just tweak it up to a steeper curve. It also helps if you
have appropriate rad sizes for the rooms, and the system is balanced.

The response curves look like:

http://wiki.diyfaq.org.uk/index.php/...tingCurve1.png

IIRC the system defaults to the 1.2 line. If you live in a super
insulted place / particularly sheltered location then you would tweak
down. In my case (exposed location - solid wall construction), I
needed to go up. I found the 1.8 curve worked well.

The system is also smart enough to automatically shift the response
curve vertically based on the currently demanded internal target
temperature[1]:

http://wiki.diyfaq.org.uk/index.php/...tingCurve2.png

So if you tweak the room temp up or down during the day (or have
different times programmed with different set point temps), then it
can vary the flow temperature to match the requirement.

[1] Note that all the system temperatures sensors (internal
downstairs, internal upstairs, DHW cylinder, and external) are
digitized and processed as actual temperatures, not just as on/off
"call for heat" style demands.


Thanks for that, interesting. And I hadn't realised such systems had a
collection of sensors.

OT but loosely relevant, I use my CH as 2 zones - upstairs and
downstairs. I'm really not going to replumb to add a properly zones
system, and I was wondering if it's possible to isolate the upstairs
zone with a three way motorised valve - simply cutting out the upstairs
'circuit'.

A single switch would be easier than faffing about with 4 TRVs each
evening.

Look at the Honeywell Evohome system
http://www.heatingcontrols.honeywell.../evohome-Main/
  #63   Report Post  
Old January 12th 19, 08:15 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

on 12/01/2019, John Rumm supposed :
So you would need a bit of rejigging to move to split temperature operation.
The VR weather comp replaces the timer and stat. You probably want a pair of
two port valves in place of the mid position valve - although with a bit of
thought you may be able to achieve the logic required with what you have.
Swap the cylinder stat for a NTC thermistor, and add a suitable wiring
centre. You would need an extra cable from the cylinder to the boiler (that
threw me, I was expecting the cylinder NTC to connect to the wiring centre!),
and to install an external NTC somewhere.

Doable enough, but whether its worth the hassle at this stage only you can
decide. It might knock a few percent off the gas bill, and will make the
place a bit more comfortable year round.


It sounds like a lot of work, just to get around a limitation of the
boiler design. I have though, my eye on a 470 complete with the outdoor
sensor.

So to check my understanding - The 470 is a complete time-clock and
system monitor and room temperature sensor built into it? With the
outdoor sensor, it becomes clever system able to adapt to set the
boiler temperature as needed. It has the built in function to monitor
an NTC on the HW cylinder and that temperature can be set separately.
  #64   Report Post  
Old January 12th 19, 09:22 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler



"Dave Plowman (News)" wrote in message
...
In article ,
tim... wrote:
Anything can work. But there is an ideal figure for rad temp for best
efficiency.


I'm not seeking efficiency


I'm seeking all of the rooms at the same temp


I'm curious about that. You said with the boiler set to 74 degrees, the
rad were too hot to touch?
How can that be with the rooms at the correct temperture if they are OK at
55 degrees?


two different boilers (two different houses)

I have yet to try the new boiler at a lower temp

tim



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Old January 12th 19, 11:19 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 19:15, Harry Bloomfield wrote:
on 12/01/2019, John Rumm supposed :
So you would need a bit of rejigging to move to split temperature
operation. The VR weather comp replaces the timer and stat. You
probably want a pair of two port valves in place of the mid position
valve - although with a bit of thought you may be able to achieve the
logic required with what you have. Swap the cylinder stat for a NTC
thermistor, and add a suitable wiring centre. You would need an extra
cable from the cylinder to the boiler (that threw me, I was expecting
the cylinder NTC to connect to the wiring centre!), and to install an
external NTC somewhere.

Doable enough, but whether its worth the hassle at this stage only you
can decide. It might knock a few percent off the gas bill, and will
make the place a bit more comfortable year round.


It sounds like a lot of work, just to get around a limitation of the
boiler design.


Not sure you can really call it a limitation of the design - at least
they provide the facility in the first place, unlike many.

I have though, my eye on a 470 complete with the outdoor
sensor.


You would probably need the VR61 or similar as well to connect to the
zone valves.

So to check my understanding - The 470 is a complete time-clock and
system monitor and room temperature sensor built into it?


Yup... and an interface to pretty much anything else the system can do.

With the
outdoor sensor, it becomes clever system able to adapt to set the boiler
temperature as needed.


Yup.

It has the built in function to monitor an NTC on
the HW cylinder and that temperature can be set separately.


ISTR the NTC cylinder sensor and the external sensor connect back to the
boiler directly, but the overall effect is the same.

You can have independent temperature settings for CH and DHW. Needless
to say that precludes the system running Y plan with the valve in mid
position, and so favours modern fast recovery cylinders. (if you program
CH and DHW to be active at the same time, it squeezes reheats of the DHW
in between periods where the CH is satisfied (perhaps with priority to
the DHW)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/


  #66   Report Post  
Old January 13th 19, 04:09 AM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On Saturday, 12 January 2019 09:28:26 UTC, Harry Bloomfield wrote:
John Rumm formulated the question :


IME many of the Vaillant boilers do support split temperature operation, but
it does depends on what controls you have them paired with.

The 400 series Vaillant I did (probably previous model range, since this was
= 12 years ago), actually had separate knobs on the front for CH and DHW
flow temperatures. Although that was retrofitted into system with
traditional controls that could not distinguish between the source of the
call for heat - hence the DHW control never came into play and it ran like
your system does.


The blurb on their web site:

https://www.vaillant.co.uk/for-insta...ler-26116.html

Seems to suggest its compatible with the VRC 700 weather compensating
controls, so that ought to allow split temperature as well.


I have studied it and not found any obvious way to split the
temperature. I even spoke to Vailant and they confirmed there was no
way it could be done.


If the Vaillant has 2 separate call for heat signals for DHW & CH it would be simple enough to split the temp, at least if the boiler has 2 separate temp settings for the 2 circuits, and the Vaillant 400 series I'm familiar with does. Where is the problem happening?


NT
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Old January 13th 19, 04:15 AM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On Saturday, 12 January 2019 13:31:13 UTC, John Rumm wrote:
On 12/01/2019 08:38, Harry Bloomfield wrote:
John Rumm pretended :


It needs a little bit of experimentation to set the profile the first
time - basically waiting for colder days and seeing if the system
still heats the place comfortably and quickly enough. If it doesn't,
then you just tweak it up to a steeper curve. It also helps if you
have appropriate rad sizes for the rooms, and the system is balanced.


Balanced?

I have always assumed there was no need to balance a system, where TRV's
are installed.


Many CH installers would probably argue that is the case... but it can
make a system less nice to live with. Especially if you have rooms that
don't get adequate flow until nearly all the other rads have throttled
on their TRVs, or worse, never get to set temp because the main stat has
turned the whole system off.


IMLE it's essential to balance the system with TRVs set to max temp before using the TRVs to improve balancing as needs change.


NT
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Old January 13th 19, 11:01 AM posted to uk.d-i-y
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Default how hot do you run you CH boiler

on 12/01/2019, John Rumm supposed :
Not sure you can really call it a limitation of the design - at least they
provide the facility in the first place, unlike many.


..All it would need to enable a split temperature, is 2x call inputs for
heat instead of the single one it has at the moment. Plus the two
temperature settings in the software, to replace the single
temperature. A fairly simple fix at the design stage.

Needless to say that precludes the system running Y plan with the valve
in mid position, and so favours modern fast recovery cylinders.
(if you program CH and DHW to be active at the same time, it squeezes
reheats of the DHW in between periods where the CH is satisfied
(perhaps with priority to the DHW)


That would not usually be an issue here. The DHW is usually brought up
to temperature in less than 20 minutes. 20 minutes with no CH input
would not be noticed.
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Old January 13th 19, 11:24 AM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 13/01/2019 10:01, Harry Bloomfield wrote:
on 12/01/2019, John Rumm supposed :
Not sure you can really call it a limitation of the design - at least
they provide the facility in the first place, unlike many.


.All it would need to enable a split temperature, is 2x call inputs for
heat instead of the single one it has at the moment. Plus the two
temperature settings in the software, to replace the single temperature.
A fairly simple fix at the design stage.


Oddly the older version of the 400 series had the separate temperature
knobs on the front, although I also have vague memories of there being
reported problems using weather compensation on those. So perhaps they
"fixed" it by going to the system used on the 600 series.

Needless to say that precludes the system running Y plan with the valve
in mid position, and so favours modern fast recovery cylinders. (if
you program CH and DHW to be active at the same time, it squeezes
reheats of the DHW in between periods where the CH is satisfied
(perhaps with priority to the DHW)


That would not usually be an issue here. The DHW is usually brought up
to temperature in less than 20 minutes. 20 minutes with no CH input
would not be noticed.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
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Old January 13th 19, 11:34 AM posted to uk.d-i-y
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Default how hot do you run you CH boiler

wrote :
If the Vaillant has 2 separate call for heat signals for DHW & CH it would be
simple enough to split the temp, at least if the boiler has 2 separate temp
settings for the 2 circuits, and the Vaillant 400 series I'm familiar with
does. Where is the problem happening?


It is a Vaillant 418 ECOfit Pure. It only has one input for call for
heat, a permanent supply, plus an output for the pump. It also only has
a single temperature setting, which I presently have set for max (75C).
From cold, the boiler runs flat out until its output nears 75C, then it
begins to modulate its heat output gradually down.

We like the HW hot, so have it set at 75C for HW. The HW is set to come
on for an hour per day, to bring the tank up to temperature, though
when more HW is needed like when taking a bath, we press a 1 hour
override button.

75C is unnecessary for the CH and not as economic as 60C would be, so I
am looking for a workaround to allow for split HW v CH boiler
temperatures.

My first attempt at a split was a disaster...

I added an adjustable thermostat to the CH pipe, just past the 3 port
valve, wired to interrupt the CH call for heat wire when the pipe got
to 60C. Which it did perfectly, but that caused the boiler to cycle
frequently on and off, as the pipe temperature rapidly cooled and
reheated. It also defeated the boiler's ramping down (modulating) its
output.

Another way I had thought of, was to fool the boilers own output
temperature sensor, so when the call is for CH, it sees a false higher
than actual temperature. I could probably manage that, with an extra
call for CH wire back to the boiler (easy), a simple relay and a bit of
jiggery pockery in the boiler sensor circuit. As it is a brand new
boiler, I am reluctant to start modifying it and risk the guarantee.


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