Instant hot water system question.

[luce.rocks]

How does a gas instant hot water system know when I turn on the hot water? What's the feedback loop from the tap to the water system? How does it know I want hot water, not cold water?

I've googled a bunch of 'how does a gas hot water system work' type questions but all results seem to give information on what they do, rather than how they do it. Any plumbers out there want to enlighten me?

 

[AJB]

When you turn the tap on, water flows through the hot water system and triggers a sensor which opens a solenoid for the gas to flow and an ignitor lights the gas.

 

[tj22]

How does it know I want hot water, not cold water?

because you turn the hot tap on?

 

[DaveM]

There are two water lines to the sink, one from hws one from the cold water main from the street.

 

[westminster]

There are two water lines to the sink, one from hws one from the cold water main from the street.

visually you can see this as

 

[luce.rocks]

When you turn the tap on, water flows through the hot water system and triggers a sensor which opens a solenoid for the gas to flow and an ignitor lights the gas.

The sensor - that's the magical part I wanted to know about. Thanks AJB! Now googling flow sensors and how they work

 

[wombat777]

A variation on this is solar gas-boosted hot water. Quite common for many new builds in Australia where areas have street gas.

I'm not sure that the gas-booster would be practical where only bottled gas is available. Does anyone know?