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.

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