How do back boilers work?

[opps]

Long story... but I now find myself living in a property with a gravity fed system.

If the back boiler is set to run from 5AM until 7AM (for DHW), I guess it sends the domestic hot water to the immersion tank. What happens when the immersion tank is full?

Sorry, I am only familiar with combi systems.

 

[cross thread]

It then cycles on the boiler thermostat unless it has a thermostat on the cylinder

 

[gas112]

What is your definition of gravity fed ?

 

[Stuckinarut]

If the back boiler is set to run from 5AM until 7AM (for DHW), I guess it sends the domestic hot water to the immersion tank. What happens when the immersion tank is full?

What do you mean by full? Fully heated or full of water?

 

[Jurassicspark]

guess it sends the domestic hot water to the immersion tank. What happens when the immersion tank is full?

That would be a pain wouldn't it?

The boiler circulates the water in the tank (mucky water likely) note that the water doesn't mix with the cold (fresh mains water) in the cylinder. The boiler keeps pumping the water around the cylinder and whewn the temperature reaches desired temp (cylinder Stat) it shuts the boiler down (if you don't have one fitted the boiler will just cycle killing efficiency)
The heated water from the boiler transfers heat to the mains fed water in the cylinder which then goes to yoir taps (clean water).

As you consume water, more will enter through the bottom of the cylinder.

 

[MNW67]

I guess it sends the domestic hot water to the immersion tank. What happens when the immersion tank is full?

The hot water you get from your taps isn't the same water that goes through the boiler. Your hot water cylinder ("immersion tank") gets filled with fresh cold water that comes from a tank in the loft. In the middle of the hot water cylinder is a copper coil. Water from the central heating circuit is heated by the boiler and it passes through this coil. This heats up the cold water in the cylinder, turning it into the hot water you get from your taps.