noisy hot water only

[jerrythemole]

Hi I fitted a three port valve to my central heating system some time ago and it all works great. The only problem I have is that when I select hot water only, a lot of noise (gurgling) comes from the system. If I select heating or heating and water together the noise goes away, it's just when I select hot water on it's own. The valve is ok, I removed it and checked it was working ok.

Does anyone have an idea what could be the problem please?

Thank you

 

[kevplumb]

air in the hot side View media item 457
do you have one of these

 

[jerrythemole]

No I don't have a vent valve. On my system the pipe goes up to the loft and vents into the top up tank through an open ended pipe.