"Tim Smith" wrote in message
...

"andrewpreece" wrote in message
...

"Tim Smith" wrote in message
...
Hi there,

I have a Vaillant Combi boiler (according to hte manual, it is eithera
VCW
GB 221H , 240H or 280H - Im afraid I cant find any indication on the
boiler
itself).

Over the past couple of weeks, I have noticed that although the boiler
is
on
for central heating, the thermostat in hall seems to indicate the
acutal
temperature is lower than the set temperature by several degrees. I do
this
by listening for the click on the thermostat so I know it isnt
incredibly
accurate. In addition, the radiators are reasonably warm.

However, today on furhter investigation, I did notice that the
pressure
gauge on the boiler is indicating just below the first mark on the
gauge
which I think is 0.5bar. The instrucitons indicate that the pressure
should
be around 1bar.

According to the manual (and fairly obvious to even my limited
knowledge)
the water pressure needs topping up. The instruictions I have
recommedn
getting a plumber to do this but I dont fancy paying someone good
money
to
do something that is probably straight forward (I have done this on a
boiler
at a previous house). The isntructions dont mention which is the
correct
valve for water inlet.

Can anyone tell me which is the correct valve to open and whether this
could
cause the symptoms I am seeing ?

Thanks

Tim



I had a Vaillant 242: in that case the filling loop was a length of
braided
flexible pipe, with one end going to the cold water inlet pipe. There
were
two knurled plastic knobs on valves at each end of the pipe, and you had
to
open both in order to get water flowing in ( I think it is two valves to
prevent back-contamination of the domestic water supply by pressurised
wat
er
flowing back from the boiler ). I believe you have to open them in a
particular order, though offhand I can't remember what order it is!

Your cold water inlet pipe, should be fairly easily identifiable as it
will
be 15mm and will be cold to the touch, if the HW and CH are or have been
in
recent use ( the gas pipe is 15mm but not so cold ). Anyway, that's my
best
to offer on the subject, perhaps someone with knowledge of the exact
model
can be more helpful. Oh, by the way, if your system pressure keeps
falling,
get it looked at, as continually topping the system up leads to
corrosion
and early failure.

Andy.

Thanks Andy,

I think I have identified the cold water inlet - as you say it is cold !
It
also has a T-joint. One side goes into the boiler (presumably for the
ho****er) and the other (via a braided pipe and two valves) connects to a
hot pipe. I guess this is teh connection into the sealed heating
"circuit".

Anyone any idea which order the valves should be opened in ? I guess they
could be defined as the valve at the ho****er "circuit" end and the valve
at
the end cold supply end.

Thanks again.

Tim


I'm not too sure that it is necessary to open them in a particular order,
thinking about it: the fact is, if you crack them both open your system will
pressurise. I may be getting confused. These filling loops have a valve at
each end so that you can disconnect them when you're finished - not that a
lot of people bother! The theory is that either yucky combi water will
feedback into the mains water if there is a leak in the filling valves/you
don't turn them off properly, or that if the mains pressure exceeds that in
your combi ( which it should do anyway ) that the system will sowly
pressurise from the mains. Once it reaches 3 atmospheres the pressure relief
valve will blow off and dump a lot of your CH system water out of the
blow-off pipe ( the blow off pipe probably exits via your wall somewhere -
it would pay to keep an eye on this pipe especially when the CH turns on of
an evening to see if it is blowing off ).

Anyway, given that you are supposed to remove the filling pipe once finished
with it, you can see that it needs a valve either end or you would have a
gusher, either from the mains cold water end, or the CH loop end. So, ignore
the fact that I talked about an order to things, and just crack both the
valves open slowly. You'll want about 1 to 1.5 bar pressure in the system.
You may have a leak in the pipework, or a punctured diaphragm in your
pressure relief vessel ( big red doughnut shaped thingy, at the back of the
combi somewhere ), if you coninue to lose pressure,

Andy.