Central Heating system problem

[jamess76]

I have a pottern suprima 70000 btu boiler, 3 port honeywell valve hotwater system is convetional cylinder with coil connected to primarys.
When the central heating reaches temperature and if the hotwater is still calling for heat a noise descriped as a bang is heared from the location of the pump/ valve/ boiler.
It is not an explosive bang but more of rickershey of water being all of a sudden stopped or valve dragged shut??
Have changed the valve and pipes seem to be secure.
The boiler has also locked out a few times and required reset
Valve seems to be plumbed in correctly
One item I have from the boiler Output flow pipe is a cylinderical copper fitting about 50mm diameter and about 80mm high not sure why. Is there a possibility that the pump control via the boiler pcb at fault? Anyone any ideas please thanks for help

 

[kevplumb]

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[jamess76]

Kevplumb

Thanks its the second one any ideas what iuts for ?


Thanks

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[seco services]

air seperator.

 

[jamess76]

Do you think this may be cause of problems ?

air seperator.