In an earlier contribution to this discussion,
Dave wrote:


Hot water heating is done via electric, not oil. The reason this was
done (despite electricity being much more expensive per kW hr than
oil), is that there is a wood burning stove too. That wood burning
stove heats the hot water too - in addition to the electric, although
the wood burner is rarely used. The plumber who fitted the oil
central heating said it would be unsafe to heat the water in the hot
water tank 3 ways - electric, wood and oil. So the hot water remains
heated by electric + wood only.

Hence I assume this means there are two circuits upstairs? I've just
counted the radiators and find there is 5 upstairs and 6 radiators
downstairs - it's a 3 bedroom detached house.

Are you sure that one pair of pipes doesn't connect the wood-burning stove
to the hot cylinder?


I'm not aware of any control which trims individual circuits.

A lockshield valve on a radiator does just that - see below.


I think I should fix these, as some of the leaks are more serious if
the control on the rad is not screwed down fully. If the manual
control is not screwed down fully but removed, water can be clearly
seen coming around the pin on two or three of these. Hence I can't
really use these rads at all.

In that case, yes! There's no point in having radiators which have to be
turned off to stop them leaking.


I'll have to check for any pyramid shape region of hot. Some seem
almost cold to me, but I'll have to double check.

It's a triangular *cold* patch you need to look for - quite wide at bottom
centre and getting narrower highter up.

I've tended to notice that neither pipe at the bottom of some rads is
warm. I'll double check this later. The heating is not on at this
minute, as the weather here is quite mild. If the rad has been
switched off for some hours, would you expect both pipes at the
bottom to be cold? I assume if no water flows through the rad, then
eventually the pipes cool. If that is not so, then it might indicate
the problem.
If there's no flow through a rad, neither pipe will be warm.



They all move down ok, and come up if pressure is removed, suggesting
a spring is used. I assumed this pin was part of the radiator and the
thermostatic control was bought as an extra and just pushed this
up/down manually. I did not realise this was bought with the
thermostatic controls. (All rads has these fitted when we had the
system installed, but as I say, they have appeared to be more
unreliable than I would have expected).

When you buy a radiator, you get *just* a radiator - looking something like
http://tinyurl.com/3lbrvc with 2 or 4 tapped holes at the corners. In order
to connect the pipes, you need valves which screw into two of the tapped
holes. [If there are 4 holes, the 3rd one has a blanking plug and the 4th a
bleed screw]. If you are controlling the radiators thermostatically - as you
appear to be - one of the valves will be a TRV, something like
http://tinyurl.com/53jgs2 and the other will be a lockshield valve,
something like http://tinyurl.com/47uox8 (when fitted with the plain cover
shown, rather than the handwheel)
The TRV has a pin inside which is pushed up and down by the thermostatic
capsule and stops the flow when the room is warm enough. The lockshield is
turned on and off by rotating its spindle with a spanner, and has to be
adjusted to a part-open state (and then left alone) when balancing the flow.


I do happen to have an IR thermometer. It basically plugs into a
digital volt meter and gives 1 mV/deg C - or something like. I
thought the area it views might be too large for a pipe, but perhaps
not if held close enough. I've also got some type K thermocouples and
a DVM which has a temperature mode which can read temperature from
these.

What you've got *may* be ok - but you really need an all-in-one hand-held
device such as http://tinyurl.com/4tbcop which enables you to zoom round the
system and measure the flow and return temp of each rad in a few seconds
each.
--
Cheers,
Roger
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