Roger Mills wrote:
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.

No, the oil boiler does not heat a tank of hot water.

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.


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.

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

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.

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.

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.

One other thing I should have mentioned is that the plumber who fitted
this said one rad should be on all the time. He suggested the one at the
top of the stairs, but we found that just made there far too hot. So I
changed that, but restricting the flow to that one and opening one up
elsewhere. That was down a few years back and worked OK, so that is not
the reason for this problem.

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.


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).

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.

OK.

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.

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.