On Jul 2, 11:47 am, Speedy Jim wrote:
The "bad smell" is very characteristic of poor combustion.
In this case, either the chimney is blocked or (likely)
the heater's central flue has collapsed.

If you remove the draft hood, you can look down the flue
in the heater to discover.

Flue collapse is caused by old age and/or very high tank pressure.

Thanks Jim.

I remember you from the aircooled VW group. Speedy as ever.
Anyway, I placed my hand over the exhaust outlet on top of the heater
and could feel hot air coming out. But judging from the amount soot
on the bottom it could easily be half plugged inside. I suppose we'll
just have to take it apart and see?

Harry