I had a win regarding the loss in pressure overnight from the main tank . After spending a couple of days with soapy water looking for air leaks , which i found none i removed the valve block and replaced the o -ring on the nrv for the tank , this is the one that faces the different direction from the other two . I have rebuilt my valve block many times over 10 years of ownership and haven't had any issues . I hope this post might help others.