"Andrew Gabriel" wrote in message
...
In article ,
"IMM" writes:

"John Andrews" wrote in message
m...
Dear all

I have a conventional heating system, comprising an Ideal gas boiler,
with gravity flow and return (hot water circuit) and pumped flow and
return (central heating circuit).

I'm getting no hot water out of the taps at present, central heating
is ok.
Can anyone advise me on how to fix this please?

Thermostat on boiler is ok, and the control panel is asking for hot
water as it should. The gravity flow pipe from the boiler is not
heating up. So I guess it might be the heat exhanger that's the
problem?

It looks like two points:

1. sludge in the gravity flow and returns

2. An air lock ( is there an air vent above the gravity pipe to the
cylinder)

3. Ball valve has got stuck up in header tank (smaller
tank), and water level has dropped below the top of the
hot water cylinder coil so it no longer circulates.
Check the small header tank.


You got to it first Andrew. It was (is) a common problem with gravity
primary hot water and pumped CH systems. It sometimes occurred with an
intermediate stage where the HW only warmed up when the heating was on and
provided just enough water movement within the boiler to persuade the
primary to move sluggishly before giving up entirely.