Open system air block?

[Blue_Manc]

I have an open system fed from a feeder tank in the attic. oil fired Boiler downstairs.

We have a hot water tank on the first floor.

All works fine when CH turned on, but when we put water only on to heat the tank we get an air lock developing at the entrance to the hot water tank. THis has to be vented there (Inconvenient location).

As I say only when Water Only only is selected, not when CH and Hot water on together.

Thoughts what to look for / check?

 

[spraggo]

I have an open system fed from a feeder tank in the attic. oil fired Boiler downstairs.

We have a hot water tank on the first floor.

All works fine when CH turned on, but when we put water only on to heat the tank we get an air lock developing at the entrance to the hot water tank. THis has to be vented there (Inconvenient location).

As I say only when Water Only only is selected, not when CH and Hot water on together.

Thoughts what to look for / check?

Your header tank is empty or you have a blockage in the cold feed from the header tank.

spraggo