"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 water
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.