Hi, and thanks for the reply
No, I can't say I tested the new thermostat before fitting. So far as I know, it was the right thermostat - what do you mean by the top hat bit?
Have you a photo of the correct orientation for the thermostat fitment?
The new stat seemed to be slightly larger in outer diameter than the one that came out. I might pull it out next weekend and test it...
The heater does seem to put out reasonable heat, but I'm used to 1960s cars which never had great heating...