As part of some renovations I've just moved a rad. in the living room,
some of the 3/4" pipe work for the old rad lead off in the direction of
nowhere in particular on taking up a few more floor boards I found it
was looping the flow and return, effectively shorting the feed to the
rads at about the furthest point in the house from the boiler. Having
removed the loop all the rads are suddenly much hotter.

I guess at some time in the past the heating circuit was changed from a
loop pipe with convection feed to the rads to a contemporary flow and
return system and whoever did it forgot about the loop . . . any other
thoughts?

--
bof at bof dot me dot uk

In article ,
bof wrote:
As part of some renovations I've just moved a rad. in the living room,
some of the 3/4" pipe work for the old rad lead off in the direction of
nowhere in particular on taking up a few more floor boards I found it
was looping the flow and return, effectively shorting the feed to the
rads at about the furthest point in the house from the boiler.

Usual practice.

Having removed the loop all the rads are suddenly much hotter.

Sounds like the system wasn't balanced.

I guess at some time in the past the heating circuit was changed from a
loop pipe with convection feed to the rads to a contemporary flow and
return system and whoever did it forgot about the loop . . . any other
thoughts?

Convection systems use *very* large pipes.

--
*Beauty is in the eye of the beer holder...

Dave Plowman London SW
To e-mail, change noise into sound.

In message , "Dave Plowman (News)"
writes
In article ,
bof wrote:
As part of some renovations I've just moved a rad. in the living room,
some of the 3/4" pipe work for the old rad lead off in the direction of
nowhere in particular on taking up a few more floor boards I found it
was looping the flow and return, effectively shorting the feed to the
rads at about the furthest point in the house from the boiler.

Usual practice.

Not come across that before, guess it saves on using a pressure relief
valve.


Having removed the loop all the rads are suddenly much hotter.

Sounds like the system wasn't balanced.

I guess at some time in the past the heating circuit was changed from a
loop pipe with convection feed to the rads to a contemporary flow and
return system and whoever did it forgot about the loop . . . any other
thoughts?

Convection systems use *very* large pipes.

I'd intended convection to the rads as opposed to the whole system, like
the 'single pipe loop' system he
http://www.diydata.com/planning/central_heating/pipework.htm which I
think was the original system in the house, which is now plumbed as the
'feed and return' system on the same page. The 'short' was a six foot
loop of pipe connecting the flow and return paths on the bottom right
rad of the 'feed and return' system.

--
bof at bof dot me dot uk

"Dave Plowman (News)" wrote in message
...
In article ,
bof wrote:
As part of some renovations I've just moved a rad. in the living room,
some of the 3/4" pipe work for the old rad lead off in the direction of
nowhere in particular on taking up a few more floor boards I found it
was looping the flow and return, effectively shorting the feed to the
rads at about the furthest point in the house from the boiler.

Usual practice.

Having removed the loop all the rads are suddenly much hotter.

Sounds like the system wasn't balanced.

snipped

Dave Plowman London SW
To e-mail, change noise into sound.

=================
This is an interesting situation in view of comments made in an earlier
thread (06/02/2005 - 11:32).

Several contributors to that earlier thread suggested that a loop without a
radiator would cause the boiler to over-heat. If those predictions of
over-heating were correct then the OP's boiler in this present case should
have been constantly over-heating because of the presence of the 22mm (3/4")
loop.

In fact it appears to have had the opposite effect since the OP states that
the temperature of all the radiators immediately *increased* when he removed
the loop. Logically the temperature of the radiators should have fallen when
the offending loop was removed because water temperature through the boiler
should have been lower when the alleged cause of over-heating was removed.

One explanation is that the effect of the loop was *neutralised* when the
system was initially balanced.

Cic.

Cicero wrote:

This is an interesting situation in view of comments made in an earlier
thread (06/02/2005 - 11:32).

Several contributors to that earlier thread suggested that a loop without a
radiator would cause the boiler to over-heat. If those predictions of
over-heating were correct then the OP's boiler in this present case should
have been constantly over-heating because of the presence of the 22mm (3/4")
loop.

Don't recall them saying it would overheat, only that it would return
hotter water back to the boiler, which may cause its thermostat to cycle
off sooner than it might otherwise...

In fact it appears to have had the opposite effect since the OP states that
the temperature of all the radiators immediately *increased* when he removed
the loop. Logically the temperature of the radiators should have fallen when
the offending loop was removed because water temperature through the boiler
should have been lower when the alleged cause of over-heating was removed.

Assuming the boiler is modulating then it would not have made any
difference to the flow temperature - the boiler would adjust the power
delivery to keep the output at a set point. IMHO, the reason the
radiators got hotter in this situation was because the loop was
unbalancing the system, and depriving the later radiators of adequate flow.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
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| John Rumm - john(at)internode(dot)co(dot)uk |
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The message
from John Rumm contains these words:

Assuming the boiler is modulating then it would not have made any
difference to the flow temperature - the boiler would adjust the power
delivery to keep the output at a set point. IMHO, the reason the
radiators got hotter in this situation was because the loop was
unbalancing the system, and depriving the later radiators of adequate flow.

ISTM that if the boiler is controlling the output temperature to a
particular figure then the higher the return temperatue the less the
actual power output of the boiler and consequentially the cooler the
radiators.

--
Roger

Roger wrote:

The message
from John Rumm contains these words:


Assuming the boiler is modulating then it would not have made any
difference to the flow temperature - the boiler would adjust the power
delivery to keep the output at a set point. IMHO, the reason the
radiators got hotter in this situation was because the loop was
unbalancing the system, and depriving the later radiators of adequate flow.


ISTM that if the boiler is controlling the output temperature to a
particular figure then the higher the return temperatue the less the
actual power output of the boiler and consequentially the cooler the
radiators.

What you are saying is correct, although it is a symptom of the
situation I described, rather than a cause IYSWIM.

The temperature of the radiator overall will be the average of the input
water temperature and output water temperature. The bypass loop will
mean the radiator is getting a low flow rate, and hence it will draw a
significant amount of heat out of the water flowing throught it. So the
exit temperature of the water will be low, and so the average
temperature will be as well (with a corresponding low flow of heat to
the room). The small flow of cold water from the radiator will then be
swamped with the large flow of hot water from the bypass, causing the
boiler to see a high return temp and to deduce the load is low. So it
will modulate down quickly and perhaps cycle off.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/