Roger Mills wrote:
In an earlier contribution to this discussion,
Andy Champ wrote:

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.

That will almost certainly be the pressure vessel - which has air on one
side of the diaphragm and water on the other, and allows the water to expand
when it gets hot. There will also be a filling loop to enable the water
system to be topped up, and a pressure gauge which shows how much pressure
there in the system. What does the gauge read (a) with the system cold and
(b) with it hot? Have you been topping it up after you have bled the
radiators?


There is a filling loop, pressure gauge and pressure relief (safety)
valve which blows at 3 bar. The pressure is about 1 bar, and rises a
little when hot.


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)

I sincerly hope that it *isn't* a series/parallel arrangement. It's more
likely to be 3 circuits, each with a flow and return pipe going back to a
central point, and with 5 rads in each circuit connected between flow and
return so that - in effect - all 15 are in parallel with each other. You
need to have a close look at the pipework to verify that because it will
affect the way you need to balance the system.


This is difficult to do, as the pipes go into the space between upstairs
and downstairs, so unless I took up loads of floorboards, it would be
difficult to know.

I know there are two pipes running close to each other which go from
upstairs to down at the centre of the house, and another two to one side
of the house. Hence there are 4 pipes connecting upstairs to downstairs.

I can't say the plumber used the term series/parallel. That is what I
interpreted it as - I'm an electronics engineer.

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.
It sounds to me as if you first need to ensure that there's adequate
pressure in the system and you then need to balance the system to make sure
that all rads gets an equitable share of the available heat. Doubtless Ed
will be along soon and will point you at FAQs about presurised systems and
about how to balance your system


There is adequate pressure. I was told 1 bar, and it is about that. As I
said, there are a couple of very small leaks which necessitate topping
this up every few months. I will fix them this week.

I suspect balancing would be useful. Some have always seemed to be
hotter than others, but in some ways that is quite useful, as one room
in particular seemed to me it needs a bit more heating, whereas other
areas less.


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.


You need to fix the leaks. Even if air does't get in, the system will lose
pressure if there are leaks and will need frequent topping up. Apart from
the inconvenience, this will also dilute any corrosion inhibitor in the
system.

I appreciate that, and will do so. I was hoping to get the bits today,
but had a lot of weight in the car (stones) and so did not wish to drive
a longer journey than necessary.


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.

Yes, sounds odd - I agree!


Any ideas what I can do to sort the problem out?
See the above comments on pressurising and balancing. You haven't mentioned
any controls which the system may have. Are there any motorised valves and
room/cylinder thermostats etc.? If you could take photos of all the
interesting bits and upload them somewhere and post a link here, that would
be very helpful.

There are no motorised valves, but there are some thermostatic valves.
The latter have been quite unreliable - the usual problem is the plastic
becomes brittle over time, then they break off. As they have tended to
develop faults, I've normally not bothered replacing them and instead
replaced them with manual controls.


The radiators have a vertical pin on one one end, which controls the
water flow. It is between around the pin that a couple of leaks have
developed. I hope these are easy to replace, and not specific to a
particular radiator type. The pipe has an OD of 15 mm at the radiators,
although some is thicker elsewhere - I think 22mm.

If that is not a sufficient description, I'll take photos later.

I assume that since I need to drain the system to fix the leaks on the
valves, it would be sensible to flush the system with a cleaner before
adding fresh water and corrosion inhibitor.

Dave