On 27/03/2018 14:03, wrote:
On Tuesday, 27 March 2018 11:45:14 UTC+1, John Rumm wrote:
On 27/03/2018 03:39, tabbypurr wrote:
On Monday, 26 March 2018 21:39:44 UTC+1, Harry Bloomfield wrote:
tabbypurr brought next idea :

My Vaillant does that.

Is that a conventional / open vented boiler, if so you need to let
Vaillant know that they do actually produce one.

I am aware that it is often fitted to sytem and combi boilers.

condensing non-combi, 400 series IIRC. IIRC it's an installed option not always present.

If you pair it with conventional controls, then it won't be able to work
out what function its supposed to be doing - so then it will use the CH
flow set point temp all the time.

I presume the boiler gets 2 separate call for heat signals, I don't remember.

Ideally it has a NTC probe connected to the cylinder, and a "smart"
wiring centre that is connected to the boiler via eBus to allow it to
control the zone valves (Y or S/S+ only I would guess).

Then it can work out what to do based on the program set on its
programmer (i.e. what times of day the DHW can be recharged), and the
input from the sensor giving the current cylinder temp. Then it will set
the valves for DHW only heating, and run appropriate flow temperatures
for the DHW reheat.

(the boiler can also control a secondary circulation pump and a recharge
pump as well if required)

It seems smart enough to not try and run both CH and DHW at the same
time (therefore avoiding running the rads at DHW temperatures), even if
the programs are overlapped. I did not realise it would do that at
first and programmed them to run at different times. These days I tend
to have DHW "on" for quite long periods shared with the heating, and
that allows it to work out when there is a big demand for hot water and
switch to reheating faster so you get more apparent hot water capacity
from the cylinder.


--
Cheers,

John.

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