On 7 Oct 2004 01:26:21 -0700, (Simon Langford)
wrote:

Phil Addison wrote in message news:
...

Have you actually followed the detailed procedure, or is the above all
you have done?

I pretty much summed up all that I've done in my first para - i.e.
just closed down the LSVs on the hottest (ground floor) rads, hoping
that would force some hot water to make its way up to the second
floor. I've not done any proper temperature readings (except using my
hand!). All of the go/return plumbing is concealed below the
flooring, so I cannot tell how the plumbing is routed. There is about
a meter of exposed 'main' pipework near the boiler and I guess the
external diameter is about 25mm.

Has it always been like this? If not, has anything been changed?

The 'about 25mm' pipe would either be 22mm or 28mm.

What diameter pipes connect to the rads on 2nd floor? If they are skinny
(8 or 10mm outside diameter) that is a likely cause, assuming you have
properly balanced the system. Even 15mm may be
pushing it depending on the length of run and size of the rads.

If that is the problem you just might be able to fix it with a more
powerful pump, but I wouldn't hold out much hope because if the pipes
are too skinny the resistance goes up *very* rapidly as you try to
increase the flow rate. The length limits for the runs are really pretty
firm, and if exceeded for a given heat load (i.e. radiator size), there
is not much alternative to replacing with a larger bore.

On the other hand it may be the pipes are OK, but you have one of the
other problems I mentioned.

If you *have* followed the FAQ procedure, it seems that there is some
inadequacy in the plumbing design. To track this down, try the
following:

Turn off the boiler.
Open both valves fully on one radiator and close down all the others.
Turn boiler back on.

If that radiator heats up, repeat for each of the others in turn.

I tried that last night - with all the others locked off, my top rads
heat up nice and hot. So no blockages, airlocks, etc.

That is a good indication (but only that) that it is just a balancing
problem. What you need to do now is *very* slightly crack open the LSV
on the downstairs rads to see if they can be got hot without
short-circuiting the upstairs loop. It is very important not to open the
LSV any more than what gives a hot downstairs radiator. Opening it too
much will give no additional benefit to that rad but will cause it to
bypass water that should be going to the upper floors.

As others have said, you do need to go further than these rough tests
and carefully follow the balancing procedure. I have high hopes that
that is all that is wrong. A £20 IR thermometer will be a great help to
speed up the process which is otherwise very tedious. If you use one, I
find a square of black PVC insulating tape stuck to the pipes to be an
excellent standard surface from which to measure the temperature.

The boiler size would only be a problem if it is firing continuously
flat out and the radiators are still not getting all equally hot.

This does seem to be the case.

Not sure what you mean. So far the rads are not balanced to equally
heat, so we cannot yet draw conclusions about the boiler.

If that does not help you will need to give us much more details of the
system and what it is doing.

OK: I have 10 rads on the ground floor (double panels ranging from
50cm to 120cm, and a 200cm single panel), 2 on the first floor and 2
on the second floor. And a chrome towel rail on each floor.

Don't forget the towel rails are rads that need balancing too. They can
also short-circuit the upper loops.

The boiler is a Worcester Highflow 400, running off LPG (costs a
fortune!). It has an built-in pump which is not speed adjustable.
(The manual says "if there is a switch, it will be factory set to
maximum and should not be adjusted".)

The whole system was brand new about 18 months ago. I had the same
problem all last winter (we had to get electric heaters on the top
floor!). Surely whoever installed it would have used an adequate size
boiler? It's physically much bigger than in my last house -- and that
was a 3-storey house too. I wonder whether the problem is that there
are so many more rads on the ground floor than on the upper floors?

Sounds like a typical installation where it is all carefully designed by
a heating engineer, and then installed by a plumber who has no idea of
the importance of balancing. In the groups experience, it seems that
virtually the only systems that get balanced are those done by DIYers.
It's probably not relevant here, but do you have a decent set of
controls? i.e. programmer, room stats, separate control over hot
water/central heating, and possibly ability to turn off
upstairs/downstairs zones?

If you can't get it balanced I should start raising hell with the
installer on the basis that it was never working to spec (e.g. to raise
rooms by about 24C over outside temp of -3C). This will be aided if you
can show charts of room temperature attained vs outside temp. The
inside/outside differential is roughly linear, so that if the rad in a
room raises it by 5C more than outside on a warm day, that is also what
it will do when it is -3C outside. So measure room temps and convert
them to what it will be when the outside is -3C and ask the installer
what he intends to do about it. These measurements should be with all
the room, TRVs and boiler stats turned to max.

Is the boiler producing very hot water at its flow, and with cool
returning water? If so the heat must be going somewhere, assuming the
pump is running!! Is it running? Can you hear it/feel it vibrating? Even
so it may still be damaged if any vanes are broken off inside. Take
the end cap off and see if the spindle is spinning - only an egg cup of
water will come out.

Phil

Phil
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