Thanks ,
Yes It does have two sets of fins
Sorry forgot to mention that we already have a plinth heater Because we never use it!
It's seems warm for about 20 seconds and cools down to room temperature when you put your hand over it.
my wife wont turn it on. She reckons it just blows out cold air on her feet! it's got to be about 30yrs old and you cant get to it at all to maintain it.
That being the case then you clearly have a flow problem that needs resolving. A plinth heater that starts hot and then runs cold is being starved of circulation water. The initial blast heat is simply the mass of metal being 'cooled'