What's the thermostat on the storage tank for?

[Londoner]

This might be a silly question but we use a gas boiler that fires up on demand and the hot water goes into a storage tank.

The boiler has it's own thermostat (1-6) that regulates the temp of the water it heats. There is also a thermo on the storage tank set to 60 deg. But what's the point of that if the heating is being done by the boiler - not the storage tank?

 

[Armo74]

The thermostat on the cylinder measures the water temperature inside the cylinder and shuts the boiler off when it reaches the set temperature which is usually about 60 degrees.

 

[Londoner]

The thermostat on the cylinder measures the water temperature inside the cylinder and shuts the boiler off when it reaches the set temperature which is usually about 60 degrees.

But isn't that what the thermo on the boiler itself is doing?

 

[dcawkwell]

The thermostat on the cylinder measures the water temperature inside the cylinder and shuts the boiler off when it reaches the set temperature which is usually about 60 degrees.

But isn't that what the thermo on the boiler itself is doing?

No the boiler is a heat source. It produces hot water at a set temperature controlled by its own thermostat. It has no concept of when other things like the house and hot water tank have reached temperature. It has to be told this by external thermostats. The water going around the boiler is separate to the water in the storage tank.

 

[Londoner]

That makes sense. Thanks.