Sorry if this sounds silly but how do you know what setting to set an automatic bypass valve at? The valve is fitted just after the pump and just after the last return tee (from the hot water cylinder). it has a red plastic cap/handle - but what setting is best to set it at? I presume it has already been pre-set by the installers but i'd like to know for future reference and so I know it will properley open when the pressure builds up from TRVs closing. I thought it a bit strange a bypass circuit/valve was even fitted, as the radiator in the hallway where the room stat is has no TRV and could act as a bypass, the boiler is a Gloworm (and obviously doesn't have a bypass built inside) which a lot of boilers do now I believe? It's just a conventional condensing boiler.