Hi all,
MY L405 pre-hater is all working fine on the timer etc, but seems only to blow cold air.
Any ideas, all input welcome!!

If you mean cold air once the vehicle is running then pretty sure it's the changeover valve on the fuel burning heater. Had the same and the valve looked fine, but changed it and warm air again! I think the rubber seals swell on the valve, causing a restriction.

As yours is the V8, if you run the car to temp and check the 2 hoses going upto the EGR valve (from the drivers side of the engine bay) in the centre of the V, if one is hot and one cold (or cooler than the other) then that's definitely your problem. L405 SV Autobiography LWB SDV8, finished in Aston Martin China Grey by ETO division.

Hi,
Thanks for the reply,
My normal heater is working fine once up to temperature.,
Its the pre-heater, it kicks in on the remote, and you can hear the burner running, but its only blowing cold air at the screen.

Got you!

The valve diverts hot water to either the block or the heater matrix, but as your normal heating works fine I'd say it rules out the valve (unless anyone knows better?). There is a coolant pump that runs in tandem with the Fuel burning heater, located just to the left of the unit, maybe this isn't running, thus not allowing the coolant to circulate to the matrix. I seem to recall the pump starts just before the FBH, so maybe start it from timed or the remote and see if you can hear the pump before the FBH cuts in. L405 SV Autobiography LWB SDV8, finished in Aston Martin China Grey by ETO division.

Thanks for this...
I have actually changed the diverter valve (LR167749) recently as wasn`t getting any heat in the car, now all working.
I bought this one earlier this year so was unaware of heating faults etc..
Its really cold here tonight so will see what happens in the morning!

It takes ages for it to actually warm up. I turned mine on this morning and 20mins later I could see it starting to defrost / melt the snow on the windscreen. By the time I got into the car ~25mins after turning it on, it was toasty. But it doesn't do much for the first 10mins or so, in my experience.

If it's still cold after 20-30mins, you've got a problem!