I've googled, read the faq's, but I still have some questions.

GCH in house, with a Combi boiler. 7 rads in total, semi-detached
house, all bar one have TRV's. Room stat present in non-rad area.
Boiler located on ground floor, has 'thick' (22mm?) pipes from boiler
which then drop via 'T' pieces to the smaller 'normal' (15?mm) pipes
that run under kitchen floor to the downstairs rads, thick pipes
continue upstairs (at some point dropping to smaller size to the
upstairs rads).

Not 100% sure of order of rads downstairs, despite there being only
two. Upstairs it's bathroom (directly above boiler location) then
through bedrooms, and then drops down to feed downstairs hall rad as
the last one on the 'upstairs' leg.

Boiler appears very capable of heating entire house and then some.
I've no cold radiators anywhere, though I suspect the kitchen one could
do with being a double rather than a single - this is the coldest room
of the house (not *that* much cooking goes on as I mostly live on my
own, plus it's north facing, and has unheated west-facing hall to side
door too).

I'm finding that the heating has to be on for 3-4 hours in order to get
the whole room up to temp. The TRV's do their thing, cycling on and
off. Lots of cycling on and off in some cases. I suspect this might
be partly down to the radiator being fiercely on due to the boiler
being so energetic (even when set to minimum), so the TRV turns off
prematurely, rad cools, room stops heating up, TRV comes on again...
only to go off again a short while later due to radiator being burnyhot
again.

So I thought I'd balance the system (it's clearly not, since all
lockshields are fully open everywhere) to see if this would improve
things.

I've borrowed one of those point-and-click temperature sensing things,
which is great. But...

What I've found is that with everything wide open, there's about a 6C
drop between flow and return at the boiler. Pump is integral to boiler
btw. On individual rads, there's a negligable drop on the return from
the rads. They'll happily sit there at around 63C both sides of the
rad, with slight fluctuation as the boiler cycles on and off. No short
cycling. Boiler apparently has an integral bypass (a bit of pipe,
unclear if there's any automatic valve on it at all). Manual also
states that a flow valve should be fitted between flow and return in
order to limit flow to acheive design temp drop across system. I
figure that'll be my bathroom rad then, since it's non TRV.

Struggled to get a 11C drop across the radiators unless they're only
just cracked open on the lockshields. Boilers rated for 11-17C drop
across the entire system, depending on rads served etc.

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. I can then get an 11C drop. When the boiler's
not firing and just circulating, the drop reduces quite a lot, though
eventually (now that I've throttled back even the bathroom rad by a
looong way) the boiler's not fired for long enough that I'm seeing a
flow of about 54C and a return of about 48C. Boiler *eventually* kicks
in and fires again. It's not overheating due to lack of flow (all the
TRVs are still wide at this point despite the lockshields beingn
throttled back a long way to almost closed for almost all rads) and
can't hear kettling either.

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?

Is it worth me throttling back *every single radiator* in order to get
anywhere near 10C drop across them, and something between 10-17C drop
across the boiler? Isn't that going to put more stress on the pump?
And will it actually improve the TRV characteristics?

I've balanced a system before in my old place, but that was a) all on
one level, b) no TRV's, c) very clearly defined system with boiler at
one end, radiators in a line away from that, thus making it easy to
balance with the furthest being fully open and still seeing a 11C drop
across it, with progressively closer rads to the boiler being more and
more throttled back.

This place? it's all bizarre and odd and a bit confusing.

Velvet wrote:
I've googled, read the faq's, but I still have some questions.

Oh, and I've just run around shutting all the TRVs to establish if the
flow rate through teh bathroom rad is sufficient should they all shut.
It's not, because it short-cycles and kettles. It's not *that* likely
during winter that it'd be on from the room stat yet the trvs would all
be shut, but it *does* happen regularly in spring/autumn, due to the
location of the room stat, and it's useful to warm the bathroom up to
help with condensation issues in there

So I'm going to have to rethink all this - it *clearly* needs a higher
flow rate through the bathroom rad, regardless of what the others are
throttled back to.

Am I doomed to failure with my thought that overly eager rads are
causing mayhem with the trvs, and open all the rads up a bit more (and
settle for a 4C drop across them, or something?)

Velvet

Velvet wrote:
(and snipped)
Velvet

Right, another idea. The bathroom rad's definitely the first to heat
up, and the only one without a TRV. What about... shutting off all
other rads, and closing the bathroom one in steps, till just before the
boiler starts threatening to kettle. That'll leave me with the minimum
flow rate (there is nothing in the manual for the boiler about this at
all!) - and I can then balance the rest of them (albeit they will be
further away from the boiler than the bathroom rad and thus
theoretically should have the LSV's opened wider than the bathroom,
which appears to mean pretty much wide enough to fit an articulated
lorry through)?

Oh, and I've read BOTH balancing faq's. I think a good thing would be
to simply reduce the pump speed, but I can't find anything in the
manual about that being possible to do on this combi (it's a
non-condensing 5-ish years old Saunier Duval SD30e, which is apparently
a Vaillant in disguise?) - it just says restrict the flow using a valve
across flow and return.

At least setting it all back how it was when I started it easy, I
suppose LSV's to fully open - no faffing about writing down number
of turns needed to close them before I started fiddling

Velvet

On 28 Nov 2006 14:51:19 -0800, in uk.d-i-y "Velvet"
wrote:

I've googled, read the faq's, but I still have some questions.

GCH in house, with a Combi boiler. 7 rads in total, semi-detached
house, all bar one have TRV's. Room stat present in non-rad area.
Boiler located on ground floor, has 'thick' (22mm?) pipes from boiler
which then drop via 'T' pieces to the smaller 'normal' (15?mm) pipes
that run under kitchen floor to the downstairs rads, thick pipes
continue upstairs (at some point dropping to smaller size to the
upstairs rads).

Not 100% sure of order of rads downstairs, despite there being only
two. Upstairs it's bathroom (directly above boiler location) then
through bedrooms, and then drops down to feed downstairs hall rad as
the last one on the 'upstairs' leg.

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.

Boiler appears very capable of heating entire house and then some.
I've no cold radiators anywhere, though I suspect the kitchen one could
do with being a double rather than a single - this is the coldest room
of the house (not *that* much cooking goes on as I mostly live on my
own, plus it's north facing, and has unheated west-facing hall to side
door too).

I'm finding that the heating has to be on for 3-4 hours in order to get
the whole room up to temp. The TRV's do their thing, cycling on and
off. Lots of cycling on and off in some cases. I suspect this might
be partly down to the radiator being fiercely on due to the boiler
being so energetic (even when set to minimum), so the TRV turns off
prematurely, rad cools, room stops heating up, TRV comes on again...
only to go off again a short while later due to radiator being burnyhot
again.

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.

So I thought I'd balance the system (it's clearly not, since all
lockshields are fully open everywhere) to see if this would improve
things.

Good plan.

I've borrowed one of those point-and-click temperature sensing things,
which is great. But...

Its called an Infra Red (IR) thermometer. Did you also put some black
PVC tape on the pipes to take readings from? IR thermometers give
strange readings off some surfaces.

What I've found is that with everything wide open, there's about a 6C
drop between flow and return at the boiler. Pump is integral to boiler
btw. On individual rads, there's a negligable drop on the return from
the rads. They'll happily sit there at around 63C both sides of the
rad, with slight fluctuation as the boiler cycles on and off. No short
cycling. Boiler apparently has an integral bypass (a bit of pipe,
unclear if there's any automatic valve on it at all). Manual also
states that a flow valve should be fitted between flow and return in
order to limit flow to acheive design temp drop across system. I
figure that'll be my bathroom rad then, since it's non TRV.

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.

Struggled to get a 11C drop across the radiators unless they're only
just cracked open on the lockshields. Boilers rated for 11-17C drop
across the entire system, depending on rads served etc.

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.

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?

I can then get an 11C drop. When the boiler's
not firing and just circulating, the drop reduces quite a lot, though
eventually (now that I've throttled back even the bathroom rad by a
looong way) the boiler's not fired for long enough that I'm seeing a
flow of about 54C and a return of about 48C. Boiler *eventually* kicks
in and fires again. It's not overheating due to lack of flow (all the
TRVs are still wide at this point despite the lockshields beingn
throttled back a long way to almost closed for almost all rads) and
can't hear kettling either.

Did you wind up the room stat? That could be cutting out the boiler.

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.

Is it worth me throttling back *every single radiator* in order to get

NO, see above.

anywhere near 10C drop across them, and something between 10-17C drop
across the boiler? Isn't that going to put more stress on the pump?
And will it actually improve the TRV characteristics?

I've balanced a system before in my old place, but that was a) all on
one level, b) no TRV's, c) very clearly defined system with boiler at
one end, radiators in a line away from that, thus making it easy to
balance with the furthest being fully open and still seeing a 11C drop
across it, with progressively closer rads to the boiler being more and
more throttled back.

The 'furhest' is the one that is having the hardest job to get hot. It's
LSV should be fully open.

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

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
The Google uk.d-i-y archive is at http://tinyurl.com/65kwq
Remove NOSPAM from address to email me

On 28 Nov 2006 17:20:06 -0800, in uk.d-i-y "Velvet"
wrote:

Velvet wrote:
(and snipped)
Velvet

Right, another idea. The bathroom rad's definitely the first to heat
up, and the only one without a TRV. What about... shutting off all
other rads, and closing the bathroom one in steps, till just before the
boiler starts threatening to kettle. That'll leave me with the minimum
flow rate (there is nothing in the manual for the boiler about this at

Yes, that would be the way to set the LSV on a rad being used as the
by-pass, but I thought you said your combi has built in bypass?

all!) - and I can then balance the rest of them (albeit they will be
further away from the boiler than the bathroom rad and thus
theoretically should have the LSV's opened wider than the bathroom,
which appears to mean pretty much wide enough to fit an articulated
lorry through)?

Just balance the rest as per the FAQ. You might finish up with a
different temperature drop across the bypass rad than all the others,
but so long as you are warm enough its nothing to worry about.

Oh, and I've read BOTH balancing faq's. I think a good thing would be

I recommend this one http://www.diyfaq.org.uk/plumbing/rad-balance.html,
but then I would, wouldn't I?

to simply reduce the pump speed, but I can't find anything in the
manual about that being possible to do on this combi (it's a

Yes, if the temp drop you finish up with is less than the 11C typical
you can reduce the pump speed.

non-condensing 5-ish years old Saunier Duval SD30e, which is apparently
a Vaillant in disguise?) - it just says restrict the flow using a valve
across flow and return.

As I said in the reply to your other post, I don't follow that. Maybe
someone else with that manual can clarify it.

At least setting it all back how it was when I started it easy, I
suppose LSV's to fully open - no faffing about writing down number
of turns needed to close them before I started fiddling

Velvet

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
The Google uk.d-i-y archive is at http://tinyurl.com/65kwq
Remove NOSPAM from address to email me

On 28 Nov 2006 15:32:46 -0800, in uk.d-i-y "Velvet"
wrote:


Velvet wrote:
I've googled, read the faq's, but I still have some questions.

Oh, and I've just run around shutting all the TRVs to establish if the
flow rate through teh bathroom rad is sufficient should they all shut.
It's not, because it short-cycles and kettles. It's not *that* likely
during winter that it'd be on from the room stat yet the trvs would all
be shut, but it *does* happen regularly in spring/autumn, due to the
location of the room stat, and it's useful to warm the bathroom up to
help with condensation issues in there

So I'm going to have to rethink all this - it *clearly* needs a higher
flow rate through the bathroom rad, regardless of what the others are
throttled back to.

The room stat should be set so that it cuts the boiler out before all
the room stats close, then this problem won't arise. It is not a perfect
solution because it means the boiler shuts down when one room at least
is still asking for heat, but short of putting in a flow detector switch
it's the best you can do.

Am I doomed to failure with my thought that overly eager rads are
causing mayhem with the trvs, and open all the rads up a bit more (and
settle for a 4C drop across them, or something?)

Velvet

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
The Google uk.d-i-y archive is at http://tinyurl.com/65kwq
Remove NOSPAM from address to email me

Correct me if I'm wrong, but I thought you must not fit a TRV to the
radiator in the room/area where your CH thermostat is located for obvious
reasons.

Martin


"Velvet" wrote in message
ups.com...

Velvet wrote:
(and snipped)
Velvet

Right, another idea. The bathroom rad's definitely the first to heat
up, and the only one without a TRV. What about... shutting off all
other rads, and closing the bathroom one in steps, till just before the
boiler starts threatening to kettle. That'll leave me with the minimum
flow rate (there is nothing in the manual for the boiler about this at
all!) - and I can then balance the rest of them (albeit they will be
further away from the boiler than the bathroom rad and thus
theoretically should have the LSV's opened wider than the bathroom,
which appears to mean pretty much wide enough to fit an articulated
lorry through)?

Oh, and I've read BOTH balancing faq's. I think a good thing would be
to simply reduce the pump speed, but I can't find anything in the
manual about that being possible to do on this combi (it's a
non-condensing 5-ish years old Saunier Duval SD30e, which is apparently
a Vaillant in disguise?) - it just says restrict the flow using a valve
across flow and return.

At least setting it all back how it was when I started it easy, I
suppose LSV's to fully open - no faffing about writing down number
of turns needed to close them before I started fiddling

Velvet

Phil Addison wrote:
non-condensing 5-ish years old Saunier Duval SD30e, which is apparently
a Vaillant in disguise?) - it just says restrict the flow using a valve
across flow and return.

As I said in the reply to your other post, I don't follow that. Maybe
someone else with that manual can clarify it.



It means using the pump valves or similar to restrict the flow rather
like you would use the valves on a radiator. I'd be surprised if the
pump wasn't adjustable but if you set it low then it means it takes
longer for the house to heat up.

I've balanced mine by feel and it seems ok. No idea what the temp
drops are.

For the "bypass" you need enough water volume so that it doesn't
overheat and boil. If the boiler gets very hot then you need more
water than it it doesn't. If you don't have enough water in the
regular pipework then a radiator will add some volume. If the bypass
loop is too open you'll get boiler cycling. if it's too closed you
might get kettling. Auto bypass valves supposedly give you the best of
both worlds - all the heat to the rads when they need it and then flow
through the bypass when they don't.

To avoid having a bypass radiator you need enough water volume in the
pipes to avoid kettling etc but it often depends on the boiler type.

adder1969 wrote:
Phil Addison wrote:
non-condensing 5-ish years old Saunier Duval SD30e, which is apparently
a Vaillant in disguise?) - it just says restrict the flow using a valve
across flow and return.

As I said in the reply to your other post, I don't follow that. Maybe
someone else with that manual can clarify it.



It means using the pump valves or similar to restrict the flow rather
like you would use the valves on a radiator. I'd be surprised if the
pump wasn't adjustable but if you set it low then it means it takes
longer for the house to heat up.

(snipped)

To avoid having a bypass radiator you need enough water volume in the
pipes to avoid kettling etc but it often depends on the boiler type.

My boiler has a bypass pipe in it, from one side of the heat exch unit
to the other, from what I can make out. It's about the same thickness
as a bit of microbore (yuck/spit/hiss) so the flow rate through it is
going to be pretty poor, and the volume of water also practically
nonexistant (we're talking maybe a foot, foot and a half length at
absolute best).

I've never adjusted a CH pump in my life so not really sure what I
should be looking at on it to twiddle. If someone could give me a few
clues as to what to look for (bearing in mind it is part of the boiler,
I know where the pump is on it - rather than being external to the
boiler type). The manual is a bit crap generally for the boiler, so
it's not completely infeasible that the pump *is* actually adjustable,
and they've just not actually said that anywhere (though the bit about
using a flow valve across flow/return does rather make one wonder).

I definitely don't have the water volume in the boilers own bypass in
order to prevent kettling, as I discovered later that night when I shut
all the trvs down fully. Even with the bathroom rad half-open on the
LSV there was insufficient flow to prevent kettling, and even when the
CH boiler stat was at minimum too.

Martin wrote:
Correct me if I'm wrong, but I thought you must not fit a TRV to the
radiator in the room/area where your CH thermostat is located for obvious
reasons.

Martin

You're right, they apparently fight. I do actually use the kitchen rad
to heat the side hall/downstairs WC at the moment, and the stat is in
the WC (conviently close to the boiler in the room next to the WC). No
rad in the WC, the side hall is heated via the kitchen, and the kitchen
is the biggest room that's also north facing, so always the last to
come up to temp despite being the 2 or 3rd closest rad to the boiler
(greatest heat losses from that room so always starts from a colder
temperature).

Despite effectively being one area, by the time the TRV brings the room
up to temp, the lag in that heat reaching the side hall/WC and thus the
stat is just right in order to then shut the boiler off. Whilst the
kitchen is coming up to temp, the other rads have been cycling on and
off quite a bit (usually prematurely, due to the fierce heat from the
rads, which is still only a theory of mine). All in all it works
really well, but only because of the specific environmental conditions
that are present with the kitchen/hall/wc/stat.

It's not practical to have the stat in the room without the TRV on the
rad - that's the bathroom, so wild fluctuations in temp due to window
being open to ventilate to prevent condensation, as well as heat from
having a bath, for example.

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

Velvet wrote (and wrote and wrote, then snipped it all).
I've googled, read the faq's, but I still have some questions.


Aha!

I've experimented, having found a control box on top of the pump marked
up with I, II, and III. No prizes for guessing which one it was set
on...

It's now set to the other end of the scale. Rads are now warming up
more in the manner I would expect (ie, I can finally be sure the one in
the hall really IS the furthest from the boiler). All LSVs and TRVs
fully open, boiler's set to max, and I'm waiting for it to get up to
temp before I shut off all the trv's and work out how far I can close
the bathroom (non trv) rad before the boiler complains. That'll give
me a baseline for that radiator, and I should (hopefully!) then be able
to throttle back all the others (apart from the index, which is the
hall) to what's needed for them to be a little more balanced.
There's really very marked difference in the flow reaching the hall rad
(water has to go up to the bathroom from the boiler, across to the
front of the house via all the upstairs rads, and then down the wall,
to the hall rad by the front door). I'm thinking I may find the pump
speed needs to be set for the middle, not sure if the up - across -
down - up - back - down to boiler again means it's still only once the
head or if it's twice...

Velvet

Well, that's interesting. With the pump set to I (lowest) the water
slowly circulates around, but seems to heat up all the rads barring the
furthest (downstairs in hall, but fed from upstairs circuit) reasonably
quickly (burnyhot within 5 minutes). Boiler temp on the flow reaches
80C and sits there quite happily while it's burning, and with all the
rads wide, it happily sits there for a good long while burning at this
temp, with the pump set to I.

This includes the two rads on the ground floor circuit, so I don't
think it's just convection doing the work - I'd expect both downstairs
rads to stay cold if that was the case due to the way the plumbing is
at the point where upstairs and downstairs diverges (sideways T with
22mm continuing up, 15mm continuing down, 22mm sideways horizontally to
boiler).

However, with all the rads shut except the bathroom (and this wide
open), the boiler kettles. Same if I have the kitchen rad wide
(closest downstairs one to the boiler, and the only other candidate for
having the TRV disabled on it). So two wide, pump on min, kettles and
short cycles. Set pump to middle and it stops the kettling, though a
little short cycling going on, with periods where it's doing it right
(and modulating up and down in the longer burn cycle).

I'm not sure where this has got me. If there were no TRV's I'd set the
pump on minimum, balance the entire lot on the basis there would
probably be enough flow with that pump speed, and if not, knock the
pump speed up to half way, and balance for that.

But the TRVs mean that if I balance the rads, when they shut down, it
throws the *entire system* out of whack, not enough flow rate through
the remaining radiator, boiler kettles, and I'm back to having the pump
on full tilt (which leads to very noisy valves, and all the other
things too).

If I leave the kitchen open wide enough to stop the kettling (in
addition to the bathroom rad being wide open), then I can see in order
for it not to turn off on the TRV it's going to be open that wide
constantly, the roomstat will have to be set to turn off before the TRV
starts to shut, which then leads to the roomstat turning off
prematurely if a) the radiator's kicking out heat at a constant rate,
b) I'm cooking, c) for some reason it's warmer in there than another
part of the house.

Fair enough that another part of the house may have TRV's 'open', but
if the flow rate through those other 'on' radiators isn't at least
equal to the flow rate lost from the kitchen one having turned itself
off (or even down), the boiler's going to start kettling again...

I know the theory behind them, but... are TRVs really such a good idea
in practice? I'm *really* beginning to wonder if they're suitable for
this boiler and this house!

Phil Addison wrote:
is still asking for heat, but short of putting in a flow detector switch
it's the best you can do.

I own this place, and I still forget that (after having rented the
previous place for 13 years) I could, should I want, fit something like
that to *my* CH

I may investigate that. And maybe those automatic bypass valve things.
If they're any good?

On 29 Nov 2006 11:00:20 -0800, in uk.d-i-y "Velvet"
wrote:


Phil Addison wrote, and Velvet snipped lots and replied at various
points:

[big snip]

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?

YES, you don't want the boiler cutting out while you're balancing.

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.

Not a temp diff, it will fire on/off according to the flow temp stat on
the boiler.

[more snip]

Phil
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On 29 Nov 2006 11:55:25 -0800, in uk.d-i-y "Velvet"
wrote:


Velvet wrote (and wrote and wrote, then snipped it all).
I've googled, read the faq's, but I still have some questions.


Aha!

I've experimented, having found a control box on top of the pump marked
up with I, II, and III. No prizes for guessing which one it was set
on...

It's now set to the other end of the scale. Rads are now warming up
more in the manner I would expect (ie, I can finally be sure the one in
the hall really IS the furthest from the boiler). All LSVs and TRVs

So you do have one that is slower than the others, therefore the system
is not balanced. Next step is to leave that ones LSV wide open and
close off the others, using a recording sheet from the FAQ to keep track
of what's happening, until that slowest/furthest one is heating as quick
and as hot as the hottest of the others.

fully open, boiler's set to max, and I'm waiting for it to get up to
temp before I shut off all the trv's and work out how far I can close
the bathroom (non trv) rad before the boiler complains.

You should still include that bathroom rad in the balancing, before you
start to adjust its control valve.

Some combis allow you to have TRVs on all radiators because they have an
internal (automatic) bypass. Are you sure yours doesn't?

That'll give
me a baseline for that radiator, and I should (hopefully!) then be able
to throttle back all the others (apart from the index, which is the

No. As already said ALL radiators should be balance first. This makes
sure they all get a fair share of the water flow. Throttling one back
afterwards is ok, as that will then just make slightly more available
EQUALLY to all the others.

Also the wider open the bathroom rad finishes up, the less kettling you
will have, though I suspect when properly balanced that problem will
disappear anyway. There is no point in turning it down to 'just not
quite kettling'. Only turn it down if the bathroom gets too hot (but
obviously no to the point of kettling).

hall) to what's needed for them to be a little more balanced.
There's really very marked difference in the flow reaching the hall rad
(water has to go up to the bathroom from the boiler, across to the
front of the house via all the upstairs rads, and then down the wall,
to the hall rad by the front door).

That's normal, and is the reason for balancing. The other rads are
effectively short-circuiting the hall one, so you have to increase the
resistance in them so they take less flow and make more available for
the hall. Once a rad has enough flow to fully heat it, giving it more
flow wont get it any hotter, but will steal flow from the furthest rads
which then wont get so hot.

I'm thinking I may find the pump
speed needs to be set for the middle, not sure if the up - across -

Use the slowest speed that all gets the rads fully hot. Rads are
normally spec'd to give full output with 11C drop across them, so there
is no point in running the pump faster than what's needed to get in the
region of 11C.

down - up - back - down to boiler again means it's still only once the
head or if it's twice...

Eh??

Phil
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On 29 Nov 2006 13:03:22 -0800, in uk.d-i-y "Velvet"
wrote:


Well, that's interesting. With the pump set to I (lowest) the water
slowly circulates around, but seems to heat up all the rads barring the
furthest (downstairs in hall, but fed from upstairs circuit) reasonably
quickly (burnyhot within 5 minutes). Boiler temp on the flow reaches
80C and sits there quite happily while it's burning, and with all the
rads wide, it happily sits there for a good long while burning at this
temp, with the pump set to I.

That's a good start, now do the balancing.

This includes the two rads on the ground floor circuit, so I don't
think it's just convection doing the work - I'd expect both downstairs
rads to stay cold if that was the case due to the way the plumbing is
at the point where upstairs and downstairs diverges (sideways T with
22mm continuing up, 15mm continuing down, 22mm sideways horizontally to
boiler).

Where did convection get in on the story? The water is pumped all round,
no convection needed.

However, with all the rads shut except the bathroom (and this wide
open), the boiler kettles. Same if I have the kitchen rad wide

Better check what you mean by kettling!! Its normal for the to make a
bit of a whistling/singing noise when its going flat out, with maybe an
occasional knock sound, but it should not be making serious
banging/clanking sounds. If it is kettling, it might be worth cleaning
it out with flushing fluid, and refilling with a good inhibitor. Google
for posts on flushing and inhibitor.

(closest downstairs one to the boiler, and the only other candidate for
having the TRV disabled on it). So two wide, pump on min, kettles and
short cycles. Set pump to middle and it stops the kettling, though a
little short cycling going on, with periods where it's doing it right
(and modulating up and down in the longer burn cycle).

Again lets check definitions: Short cycling occurs when the flow rate
through the boiler is insufficient to take away the full heat from the
flame, so the temperature rise across the boiler is too great ant the
flow reaches the max stat temperature and cuts it out while the return
water is till not up to temperature. The cool return water cools it and
so it fires up again. With the specified (ie max) flow rate the rise
across the boiler the rise is normally only 11C so the flow temperature
slowly rises as the rads heat up, and is only a steady 11C above the
return.

Shutting down rads obviously reduces the flow rate, and can cause
short-cycling if the bypass is inadequate.

I'm not sure where this has got me. If there were no TRV's I'd set the
pump on minimum, balance the entire lot on the basis there would
probably be enough flow with that pump speed, and if not, knock the
pump speed up to half way, and balance for that.

Nearly! Set the pump on slow, then balance, then speed the pump up is
the overall drop is above the 11C figure. You do not need to achieve
exactly 11, just equal across each rad.

But the TRVs mean that if I balance the rads, when they shut down, it
throws the *entire system* out of whack, not enough flow rate through
the remaining radiator,

No, the system is still balanced. Shutting some rads down simply mans
more pressure available to supply the remainder.

boiler kettles, and I'm back to having the pump
on full tilt (which leads to very noisy valves, and all the other
things too).

Yes, could be. See above. However, the house room-stat is supposed to
turn off the boiler before all TRVs close. And incidentally, the TRVs do
not normally close completely, they shut down linearly to allow just
enough water through to maintain the room at the set temperature. I know
you say yours are going on and off, but I don't know why. See if
balancing sorts that out.

If I leave the kitchen open wide enough to stop the kettling (in
addition to the bathroom rad being wide open), then I can see in order
for it not to turn off on the TRV it's going to be open that wide
constantly, the roomstat will have to be set to turn off before the TRV
starts to shut, which then leads to the roomstat turning off
prematurely if a) the radiator's kicking out heat at a constant rate,
b) I'm cooking, c) for some reason it's warmer in there than another
part of the house.

Indeed, choosing a place for the room stat is a problem. The usual
solution is to make the hall rad the non-TRV one and fit the stat in the
hall - but not too close to the rad. A more recent option is to get a
wireless room-stat and try it in different places.

Fair enough that another part of the house may have TRV's 'open', but
if the flow rate through those other 'on' radiators isn't at least
equal to the flow rate lost from the kitchen one having turned itself
off (or even down), the boiler's going to start kettling again...

I know the theory behind them, but... are TRVs really such a good idea

Are you sure? You don't see to grasp that they are linear devices, and
if they are banging on/off something is wrong.

in practice? I'm *really* beginning to wonder if they're suitable for
this boiler and this house!

Phil
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Velvet wrote:

However, with all the rads shut except the bathroom (and this wide
open), the boiler kettles. Same if I have the kitchen rad wide
(closest downstairs one to the boiler, and the only other candidate for
having the TRV disabled on it). So two wide, pump on min, kettles and
short cycles. Set pump to middle and it stops the kettling, though a
little short cycling going on, with periods where it's doing it right
(and modulating up and down in the longer burn cycle).


I wonder if the system is clogged up a bit and/or the high temp stat
isn't working or there isn't one fitted. You could modify the bypass
to avoid havign the microbore and maybe fitting and auto-valve would
mean that the super-hot feed water gets fed back into the boiler and
it'll then shut down rather than allowing the water to overheat.