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Hi Paul, Thanks for your thoughts. I've been doing a bit of sleuthing. My Dad is in an old peoples home. The problem (with a single exception) has only happened when my car has been parked at the home which is on a compact site. The home uses pagers to summon staff to attend to residents. The pager is an Astra 6000 On Site Paging Transmitter, broadcasting at a frequency of 459.2750Mhz with a range of 1000 metres. http://www.mbelect.demon.co.uk/pager.htm I visit Dad every day so there is ample opportunity for the pager transmitter to cause mischief. The problem has NEVER happened at my own home or in any other location than at the home (with the single exception). I think there are good grounds to point the finger of suspicion at this device. The pager transmitter broadcasts very intense bursts of data. My hunch is that when the engine is being started, the computer controlling the heating and ventilation system is initialising itself. The electro-magnetic pulse given off by the pager corrupts data or program and causes that computer to lock up. I then have to wait the 30 minutes for the car to reset its electronics before the heating system will work properly again. I take care to ensure that 'OIL OK' is displayed and the warning light test display goes off before turning the key to start the engine so that the electronics can initialise before the voltage wobbles when the engine is being turned over by the starter motor. The problem has been apparent since the car was nearly new and has occurred regularly over the past 32 months. My guess is that Citroën has not produced sufficiently effective arrangements to screen the vulnerable electronics.

Now and then, after the engine has been started, the heating system refuses to respond to the controls. This evening, none of the controls (including the rear window heater) had any effect - there was no confirmation on the display panel. After switching off the engine and waiting 30 minutes for the computer to reset, the heating system worked as it should. A few weeks ago, the controls seemed to function but only cold air was produced regardless of control settings. The problem always goes away after waiting 30 minutes from switching off the engine. Has anyone else experienced anything like this and, if so, do they know what the cause was? The car works well apart from this difficulty. I have suspicion that the problem is due to RFI (radio frequency interference). It never happens at my home. So far, all but one of the instances have commenced at one location and there is known to be a low powered radio transmitter for portable communication devices in use at that place. My guess is that some parts of the car's electronics need better screening but there is no channel of communication open to a customer to pass information or comments about the circumstances of a problem directly to Citroen's technical people. As a final comment, it does seem remiss of Citroën not to provide an under bonnet switch to force a reset of a car's electronics so that a software glitch does not result in an enforced and unwanted 30 minute wait before the vehicle is once again driveable.

C5 Mk2 1.6HDi 110bhp suffers from intermittent brief hesitation of power output which always resumes almost instantly. Seems to happen at around 2000rpm to 2500rpm when accelerating. My imagination has it that the ECU is getting confused: I drive with a very light right foot. The behaviour has been with the vehicle almost since new. After a recent 25000 mile service, the problem was dormant for two weeks until I had done a long motorway run whereupon it returned. I understand that the ECU adapts to the way the car is driven. No problems have been revealed by the dealer's diagnostic equipment (surprise?). The general engine performance is magnificent. Torque is amazing and the engine pulls strongly from 1100rpm. Power at speed is very good for such a modest capacity engine. Fuel consumption is around 50mpg.