aerated hot water

[treacletart]

we fitted a new hot water cylinder and immersion heater
but the hot water comes out murky fading to clear in about 2 mins clears from bottom upwards

 

[Dan Robinson]

Wouldn't worry about it.

 

[Space cat]

It's dissolved air. What's happening is that the water has rather more air dissolved in it than it can hold. The drop in pressure as it comes out of the tap, probably aided by the roughness around the tap spout itself, prompts it to release this air as a mass of microscopic bubbles. It's a 'problem' more often seen in cold water straight from the mains supply.

Edit:

An afterthought. Bubbles can't easily form in clean water in a smooth walled container. That's because surface tension raises the pressure inside any microscopic bubble, making it much harder to get the bubble started. A rough surface gives the embryonic bubbles a head start. (If you've ever tipped some salt into a pan of boiling water, you'll know what a difference it can make.)

Your old cylinder and heater would have had many rough surfaces on which air bubbles could form as the water heated up. My guess is that your new one with its nice smooth interior is allowing more air to remain in the water.