I then moved onto the next job whilst I decided what to do next.
When I first got it home and started I noticed there was no water coming through the tell-tale so first thing was replace the impeller which was easy enough although you have to disconnect the drive linkage which involves taking the starter motor off but as that's only two bolts is easy enough
Old impeller was knackered and one of the fins was split through and barely held on, got it back together and still no water coming out???
I removed the thermostat and ran without one in, still no water!!
Blew down the tell-tale tube and could hear air escaping from around mid way down the leg (where the exhaust port is) so my best guess is the water tube which locates when the lower unit is replaced is not seated properly so now I have to remove start and lower unit again to investigate
I also put the garden hose on and back washed the system but all the water came out the bottom of the lower unit.
I also took the opportunity to clean up the t/stat and check its operation in hot water and seems to expand and contract fine.
To top it off after all my hard work cleaning it its now filthy from all the penetrating oil and getting and out all day long!!