In an earlier contribution to this discussion,
Dave wrote:



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.

That sounds ok.



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.
Does the boiler also heat a cylinder full of hot water (I assume it's not a
combi)? If so, 2 of the pipes could be for a HW circuit between boiler and
airing cupboard.

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

The usual arrangement is to connect one side of each rad to the flow pipe
and the other side to the return pipe. The electrical analogy is several
resistors connected in parallel between +ve and -ve. To continue the
analogy, you might have a trimming resistor (analogous to a lockshield
valve) in series with each resistor to allow the current (water flow) to be
balanced across all sub-circuits.



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.

It it literally only needs topping up every few months, fixing the leaks is
not that much of a priority - I'd get it working properly first.

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.

Are the radiators hot all over? If so, balancing would be a good start. If
there's a cold pyramid shaped patch at the bottom, it could be that they're
sludged up and need flushing.



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.

I presume that you're referring to the pins in the thermostatic valves - in
which case they're not part of the radiator per se, but a separate
replaceable component? The thermostatic part of the valve (the
plastic-enclosed capsule on the top) moves the pin up and down to shut off
the flow when the room is hot enough. These pins can sometimes stick in the
closed or partially open position - which may perhaps explain some of your
symptoms. With the capsule removed. you should be able to push the pin down
against a spring - and it should pop up again when released. If it doesn't
do this, get a couple of small hammers and simultaneously tap both sides of
the valve lightly to see whether you can free it.

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

If there are no controls other than TRVs, it's probably not worth it.

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.


Unless it's obviously sludged up I'd try to balance it before ripping it
apart, having first made sure that the pins in the TRVs are free.

To do a proper balance, you need an infra-red thermometer so that you can
quickly measure the flow and return temperature of each rad - but you can do
a crude balance simply by feeling the rads and progressively turning down
the lockshields on the hottest ones until they all feel more or less the
same.
--
Cheers,
Roger
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