the most common reason is a blocked heater matrix, usually caused by age or radiator sealant used to fix a leaky radiator...its just worked too well and blocked the wrong hole!!..
to fix it you need to drain the whole system and disconnect the matrix hoses at the in and out points at the bulkhead just at the back of the airbox under the windscreen.Once disconnected,flush through for up to an hour with a garden hose on reasonably high pressure.This sould work....it did for me.
colin, November 2005
