OK so you can prioritise hot water with a simple diverter valve but
don't jump in with a Heatmiser UH4 set up!
The R. Cott. heating system now works but wasted 2 days of electrician
Detail available if anyone interested.
Further question arising from a perceived risk to underfloor pipe work
if the mechanical thermal regulator fails.....
The suggestion is to fit an *over temperature* cut out to the manifold
pump. Not good for me because the diverter valve circulates water at 70
deg. plus during overrun when the DHW stat opens. My Viessmann boiler
offers weather compensation and I am wondering if this can be adapted to
give a *set back* output temperature for the underfloor system. Easy
with a combi but system boiler...?
On Sun, 20 May 2018 21:45:02 +0100, Tim Lamb wrote:
Presumably a thermostatic mixer valve fo some sort. Pretty damn
I'm assuming the "manifold pump" is a seperate pump just for the
underfloor heating system and there is a another pump doing the
overrun. If so a pipe stat set to 50 C (?) mounted on the output side
of manifold pump (or input to the manifold) with its normally closed
contacts in series with manifold pump motor? Crude but effective.
Thinks a bit more, better to put the contacts in the underfloor
heating stat circuit so if the water to the floor gets to hot it
turns off the demand thus stopping the pump and boiler. This would
obviously cycle as the pipe cooled and the pipe stat contacts
re-closed but ought to limit the max temp of the water in the
underfloor system. You could make it latch to off by adding a relay
but then you'd lose heating until reset. A latching indicator that
the pipe stat has operated might be useful otherwise you may not
notice that it has/is.
That idea will do that, but not a good idea so far as the boiler is
concerned, to frequently cycle it like that.
My boiler has only one boiler output temperature setting on it (New
heat only type). I wanted separate settings for output temperature for
CH v HW, so decided set the boiler to max, then have a separate stat on
the pipe for when the demand was for CH only. It caused rapid boiler on
/ off cycling and defeated the boiler's output modulation system.
The pump run on, quickly pumped the cooled water back round, so the
boiler fired up again, the pipe stat opened, stopped the boiler and so
on as it repeated until the room stat was satisfied. I quickly removed
the pipe stat.
On Mon, 21 May 2018 10:36:01 +0100, Harry Bloomfield wrote:
Agreed, I'm having similar battle but the otherway round with the
boiler and thermal store, the max temp from the boiler is lower than
what I'd like the thermal store to be for the CH circulation.
Setting to max was probably the mistake, as it runs and slams into
the overheat stat rather than detecting it's getting close to the set
point and modulating back.
Thinking a bit more the "don't let the floor get too hot" pipe stat
ought to be post mixer valve pre manifold so it monitors the actual
temp of the water circulating around the floor and never actually
gets hot enough to open. Rather than the flow into the underfloor
system from the boiler, pre mixer valve.
A TRV is a *room* thermostat, not a radiator thermostat.
I did some experiments when I first installed my central heating,
and they are incredibly accurate - the TRV4's were achieving a very
stable temperature with only around 0.3C drift, which is well better
than most wall stats manage. I had been rather sceptical of them
until I actually measured their performance.
BTW, nice thing about my heating system was
a) I designed it for efficient condensing operation, i.e. large
radiators which therefore don't need to be very hot, and
b) The beta version of the Myson heat loss calculator I used
over estimated all the building material heat loss values,
probably deliberately to make you buy bigger Myson radiators
than you really needed.
This actually meant the system is even more efficient than intended.
The net effect was the heating system will keep the house warm at
-3C outside running at 45C flow temperature, and you can't really
burn yourself on that. (This is ideal where young children or elderly
are around.) However, I can bang it up to max to heat the house up
from cold extremely quickly, fast enough that it's not really
necessary to turn the heating on before ariving home (although
I can do that too). The boiler's max flow is 83C, although I
can't get it quite that high with all the radiators on because
they would give off more than the boiler's max power output at 83C.
IIRC, I can get them up to around 77C at max boiler output.
[email address is not usable -- followup in the newsgroup]
New to me:-) With two manifolds, I have two mixers.
That is the right advice. However, thermosyphoning (if that is the word)
leads to the upstairs manifold slowly reaching flow/return pipe
The mixer valve is directly coupled to the pump and close to the only
practical place to fit an overtemp stat.
I am hoping a *set back system* on boiler output might be easier.
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