Because height is what it provides.

Head to something below it.

Or somewhere for expansion to go.

Neither needs much water.

Both need altitude.

Two jobs for a vented heating system.

It tops up the circuit.

And receives water as it heats.

Most of it is deliberately empty.

Waiting for that expansion.

Because a roof space is unheated.

And the tank sits in it all winter.

So insulation and a lagged feed.

Are not optional in a cold climate.

A frozen feed can empty a system.

In summer, yes.

A loft gets hot, and so does the tank.

Which is a problem for stored water.

Insulation works in both directions.

It is not only a frost measure.

Not directly - a platform across them does.

Not resting on the ceiling below.

Nor on two bearers under a plastic base.

The load arrives only when it fills.

Which is when it will show.

The damage is to everything beneath.

A stuck valve empties the mains.

Through a ceiling, for hours.

It is the commonest serious escape.

In a house with a loft tank.

On a heating system, often yes.

A sealed system uses a pressure vessel.

At low level, in the plant space.

Which removes the loft tank entirely.

And most of these problems with it.