"Ernie Bilko" wrote in message
...
I have an oil fired boiler system with two circuits, both pumped. One
drives the rads - which works fine, the other goes to the hot tank.
Since September I've had no hot water from the tank. I fitted a new
pump but no joy. What happens is this:

When the boiler has been running for a while the feed to the coil gets
hot as expected but no matter how long the boiler runs, all day even,
the return is always cold. If I switch off the pump I can hear the
water "falling" back down almost like the pump has been pushing
against a blockage.

So I drained the system and disconnected both ends of the coil and
there is standing water at both ends. I would have assumed that the
coil would have drained out via the bottom pipe when I emptied the
system, is this correct?

Does this all seem like the coil is blocked inside the tank. If so can
it be unblocked or is it time for a new tank.

House was built in 1995.

Blow through it. Does the pump have a check valve? It should as two pump
systems require one after each pump. Check that the valve is OK.

It will not be scale as it is on the primary side. It the system full of
sludge?