Blocked hot water system

[petit_pablo]

Is there any chance of you provding a picture of your HW tank, the pipes etc.

I would drain the system down and remove the cylinder connections and start hunting for that blockage.

 

[Theeagle]

Pictures would be difficult and not show very much
Is a sludge remover worth a try?

 

[petit_pablo]

Is a sludge remover worth a try?

If there is no circulation, then sludge remover wont do owt