Hi Tony, 
Just had another small thought. It sounds like you did'nt have problems with over heating, how ever, at this stage I would change your thermostat for one that is fully open at 74 Degrees centigrade (which equates to 180 Degrees fareinheit). 
Keep us posted 
Keith ( from a very wet and windy UK)
		 
		
		
		
		
		
		
		
		
	
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