Thanks for your reply Paul.
As you say, it does seem to run warm and I suspect it has something to do with the flash being powered by the camera battery and being put under more load.
In any case, the results are fine so I'll stop worrying!
|Thunderheads With Egret by Buzz Lightyear|
|Double Rainbow; Abiquiu, NM, USA. by abiquiuense|
from After the Rain
|White Tern-2289 by vbuhay|
from A Whiter Shade of Pale