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