Peter - you can chack for water flow when the temp climbs by looking in the top of the rad .... sometimes on the first use air gets trapped under the thermostat so that the temp isn't transferred to the stat button by water contact and it doesn't open - if you drill a small hole in the flange beside the flap it allows that air to be pushed past the stat so the water contacts the whole thing to properly heat it up to opening temp
Bill
