Causes of header tank (for BM2) getting hot

I note that others have experienced this problem. If there is no continuous operation of the header tank overflow what else can cause this? Could a leak be so small that it would not be detectable at the overflow eg evaporation before dripping.

Is it possible for the store temperature to be too high eg defective store stat? such that the expansion pipe did not pass water to the header tank but being metal transferred heat to it. The external part of the expansion pipe certainly can get too hot to hold.

The header tank will get hot.
But if there was sludge present in your system / unit then you may get more "venting" than usual.
Mike
MGC/H2O
Norfolk

Mike

Thank you for prompt response.
It is only in the last few days that the header tank has got hot. However, you mentioned sludge. When I tested for blockage in the internal feed pipe (from header to store), I remove some store water using the drain cock at the bottom of the store. The first third of a bucket removed was quite thick with sludge. Since 1995 that drain cock has not been used.
If it is usual for header to get hot how does that happen? I presume that the the top of the tank is insulated. Is it simply convection flow as the feed pipe obviously is full of water that can rise (convection) up.
Perhaps the store thermostat is defective. How can that be tested?