heater problem ??

Hi all my heater has started to play up, when i go around a r/hand corner i have heat but as soon as i go around a l/hand corner it goes, the heater works fine when i put it on high , either side , and i dont lose heat when i go around l/hand corners and the fan runs ok its just starting to bug me now so any ideas what it may be.
ps i have checked for leaks and everything seems ok.

only go round r/hand corners? A roundabout would be ideal to warm up, then head for the next one! Range Rovers can drive you round the bend!
Wife thinks you have a disconnected lead? What does you temp guage read? does it stay in the mid position? Have you checked the water level in the expansion tank?
Disconnected lead: perhaps you should put the blowers on max and see if either side is working when going round the bends!

thanks for the reply, the temp stay just below half way but no great water loss. both sides seem ok when they are on high plenty of heat comes out even round the bends.