prthomas

If you turn off the right hand service valve off this would stop anything passing down the heating if you then have hot water you could have a problem with the diverter valve but it is unusual on that model.once you have checked that you need to check the gas burner pressures min 1.5 max 7 the book says 5 but trust me,the chances are the gas pressure is incorect .if that is ok then I would be looking at the domestic hot water heat exchanger not transfering the heat this would allow the boiler to run very hot and sometimes shut down for short periods before cutting back in again,Im presuming all other taps are the same?and that the problem is not with the shower passing cold water into the hot which will blend and give the same effect its difficult with limmited information and also not being there hope this helps
Dave

hi, i have a Vaillant VCW GB 242 EH boiler.

we are getting hot water for about 30 seconds, then it starts to go cold. eg: the water in the shower is fine then it goes tepid at best after 30sec, even when the hot is on full.

i have been told that this problem is the diverter value, is this correct?

if so, does anyone know what is the rough cost and best option to rectify the problem?

any help would be much appreciated!