Hot water on central heating boils over

Hi
I have a ideal classic ff250 , cylinder, just had fitted
New pump
New cylinder stat
Thermostat sensor in boiler
New fan
3 way valve as it was stuck after summer seimens 3 way valve fitted

The central heating on rads works fine
Tried both on together and separate no effect
Stat in boiler at 4 out of 6

But when water comes on to heat up it runs fine until the pipes and hot water starts "whoosing" then comes the pipes banging - Temp on cylinder set at 50
Then it trips the over heat on boiler

I have had a corgi approved guy do the work but even he is stumped

If when its starts whoosing and boiling over I turn stat on cylinder down it knocks off fine -

The pump is set on medium speed

I am stumped
Help please

I'm going for blockage in pipe work, also turn down your pump and see what happens.

Andy

Hi
Have tried all 3 settings still same

How and where as water comes out ok from tap no pressure loss

How can the pipe if blocked be unblocked
Thanks

Can you post some pics of your pipework? I wondering if the open vent is positioned right.

Pipe work been same for 13 years not altered all been ok up till 4 week ago