Dave wrote:
I have an oil-fired central heating system. Most radiators are either
luke warm, or cold. One or two are hot.

The house is on two level. The system consists of

* Oil boiler
* Water pump
* About 15 radiators on two level.
* Each radiator has two valves - one user adjustable, and the other
which requires a spanner to adjust.
* Two drain points, both on the lower level.
* Presurised system
* A 'tank' of some sort, although I don't think it is a tank. I believe
there is some sort of membrane in it, which expands/contracts with water
pressure. It has a bleed screw on the top (just like radiators) and also
a much larger screw which I have no undone. I'm wondering if this might
be sensible to do.

As far as I am aware, the radiators are arranged in a series/parallel
arrangement. i.e perhaps 5 are in series, then another 5 in series, then
another 5 in series, but the groups of 5 are in parallel. This is what
the plumber who fitted this said, although I have no idea of the exact
arrangement. (He is now dead, so no chance of asking him)

The pump was making a funny noise. Hard to describe, but no usual sound.
I thought the pump was faulty, so replaced the pump, but it made no
difference.

All the radiators have been bled, although perhaps not correctly. For
example. Is there any set order - for example do upstairs, then down? As
I open the bleed screw, each lets out water, with no hissing sound
suggesting air is coming out.

Two radiators upstairs are getting hot. Most others are luke warm at best.

I am aware of a couple of radiators which has slight leaks. Perhaps air
is entering there? I can't see how air can enter a pressurised system,
but I believe I have read it can.


What I find odd is that some radiators have clear water when I open
them, and others seem to have different colour liquids. I don't believe
the water is circulating properly.

Any ideas what I can do to sort the problem out?

x-posted to uk.d-i-y where people who know more than me hang out.

Andy