How to fix new kitchen mixer tap with no hot water?

[PaulD1961]

I have installed a new replacement mixer tap in the kitchen to a house that has an instantaneous gas hot water system. The old tap worked fine but broke at the base therefore requiring replacement. The new tap will not flow hot water only cold so i suspect there is insufficient flow to get the gas system to ignite. I suspect there is a fault with the new mixer tap. 

[MitchellMc]

Welcome to the Bunnings Workshop community @PaulD1961. It's terrific to have you join us, and many thanks for your question about mixer taps.

You might need to check the specifications on your hot water unit to determine what amount of flow it requires to ignite. These systems typically require a minimum flow rate to trigger heating, and if the new tap restricts water flow more than the previous one, it could prevent the system from igniting. A brief search suggests that they should be triggered by 2.7L/min, though some units might require a higher flow.

Most modern sink mixers are designed with water efficiency in mind and often have a flow rate of around 5L/min. However, even at a lower setting—such as 3L/min—you would generally expect enough water movement to activate the system. If you haven’t already, it’s worth fully opening the hot water side of the mixer to see if that makes a difference.

You might also want to compare the flow rate of the new tap with your old one (if you still have it available) or test another tap in the house to confirm whether the issue is isolated to the kitchen mixer. If other taps are providing hot water as expected, it would further indicate that the new mixer could be restricting flow too much.

If you suspect the mixer tap is faulty, it would be best to return it to the place of purchase for assessment. You could also try temporarily removing the aerator or any flow restrictors to see if that improves the flow rate enough to activate the hot water system.

Please let me know if you have any questions.

Mitchell