Phil Addison wrote, and Velvet snipped lots and replied at various
points:
The physical ordering is of no consequence. Just feel the flow and
returns as the system warms up. If all valves are fully open, the last
to warm up is 'furthest', and its LSV should be left fully open.
I know which is the furthest - the thing is that even with all the
LSV's fully open, within just a couple of minutes there is very little
difference in flow/return over even the furthest radiator?
Hadn't put black pvc tape on the pipes to measure though. They're
painted white. Was wiggling detector around and making sure it was
very close (but not touching) in order to get reading off the pipe
rather than pipe & skirting behind. I'll black tape them tonight and
see if it improves things.
I'm puzzled by that. TRVs are not on-off devices so they should not
cycle. They are linear and gradually reduce the flow as the room heats
up, until the flow is just enough to maintain the required room
temperature. I suppose what you describe could happen if for reason the
heat from the rad is directly affecting the TRV, say if there is a
draught blowing hot air on it. It is never ideal having them so close to
the rads as they necessarily are fixed, as they are supposed to sense
the room temperature not whether the rad is hot or cold.
They do gradually close down, but they seem to close down before the
room is up to temperature. The radiator goes cold (well, usually cools
as far as slightly above room temp) and the TRV opens up again,
radiator gets toasty again, TRV starts closing down again. The house
has DG so it shouldn't be all that drafty, and I have the doors closed
on all rooms (bar the livingroom-kitchen door, just due to being in/out
often).
It's as if the room is being heated in a staircase effect. Blast of
heat, TRV closes, heat circulates around rest of room making it a bit
warmer (we're not talking huge rooms here either, standard 3 bed 1930's
semi) - area around rad cools down from what it was, TRV opens up
again, blast of heat released, TRV shuts down again whilst heat makes
it's way into room (this isn't happening over the space of just a few
minutes, but neither is it taking half an hour to shut the TRVs off).
I don't understand what this 'flow valve between flow and return' might
be. It sounds as if they mean bypass, but you say that is integral. It
is common for the bathroom rad with no TRV to be used as a bypass. On
the other hand you say there is a room stat; the rad in the room with
the room stat should have no TRV.
I think they mean a bypass. Though they seem to be saying 'adjust it
so the heat loss across the boiler is between 10-17C, and these are the
available pump head's you'll have 'spare' at any point on the graph'.
The bypass in the boiler is incredibly small and can't see it actually
functioning to avoid kettling. Think microbore sized pipe from one end
of heat exch to the other. That's the 'bypass'. There's no adjusting
valve on it at all.
Forget about 11C drops - as I say in my FAQ there is NO requirement for
that - it is a common misconception. The aim is to achieve EQUAL drops
across all rads, whilst one rad (or more) has its LSV FULLY OPEN. You
need to ensure the TRVs don't close at all during balancing. Open them
to max settings, or preferably loosen or remove the TRV head to ensure
this.
Yep, I did make sure all TRVs were fully open. Couldn't figure out how
to get the heads off, so I settled for windows open on a cold night
(not too breezy) and all cranked to max. With all LSV's open, the most
I can get is a 7C drop across the entire system (though I'll re-measure
with black tape!). Over any radiator, it's barely measurable. Less
than 1C in most cases. I think this means the pump's too fast, but
can't find anything in the manual about adjusting that as I said
elsewhere.
What I'm struggling with is the drop measurement though. If the
boiler's firing, it's quite a long cycle, and it brings the flows up to
about 62C at each rad.
62C is rather low for flow temperature if the boiler is set to maximum.
Is that the highest it ever reaches?
Nope, that was the boiler set on middle-of-the-road. Should it be set
to maximum when balancing it all?
Did you wind up the room stat? That could be cutting out the boiler.
Yep, it definitely wasn't cutting out from the room stat. Can't find
any info on what temp diff the boiler would decide to re-fire to heat
the water again from the manual. I suppose the expected drop temp has
a bearing on that figure, so maybe I can deduce from that.
So, when measuring this drop, at what point in the cycle do you do it?
with the boiler firing, so you get maximum input, and wait for maximum
temp of return from the radiator?
See FAQ. You want the boiler firing, and wait long enough for all flow &
return temperatures to settle to a steady value.
Ah, I must have missed that in the FAQ. Not sure I'm going to be able
to do this then, but I'll crank the boiler up to max and have another
go - I think in the past even on max it tends to push out enough heat
fast enough that it will soon cycle off again. Maybe it's massively
overspecced for the CH demands the rads are placing on it vs the HW.
All the rads are singles, apart from the front hall (which heats stairs
and landing). Most rads are 3' long single or smaller, the only
exception is the hall double is a 2' double, and the livingroom a 6'
single.
Is it worth me throttling back *every single radiator* in order to get
NO, see above.
Didn't think so
The 'furhest' is the one that is having the hardest job to get hot. It's
LSV should be fully open.
None of them struggle to get hot, they're all really very good at
getting hot (the kitchen one is undersized for the room I think, it
gets plenty hot, it's just a cold room, same size (and a bit more) than
the livingroom, yet about 1/3 the area of rad to heat it). It's just
the way the TRVs seem to be acting before the room heats up that's been
annoying. And the fact that I knew every LSV was wide (I'm beginning
to think that doesn't actually matter in this instance though!).
This place? it's all bizarre and odd and a bit confusing.
I think you need to read the FAQ again!
http://www.diyfaq.org.uk/plumbing/rad-balance.html
I will do. Yours was the one I read to start with that helped out a
lot. Though I'm not sure the black tape or boiler being on max was
mentioned in there - I could be wrong though!
Thanks for all the replies, I know it's been done to death here time
and time again, so I really do appreciate people still being willing to
reply and help me see the wood for all the trees
Velvet