Combi boiler - heating not working

[Merton69]

Hello
The heating side of my Ariston Combi A23 has stopped working since a new 3 way valve has been installed.
It's been a hugely reliable boiler up until now with regular servicing.
When the heating is turned on the boiler ignites and looks to start up but then a few seconds in, knocking sounds comes from the boiler and kind of makes it's way down to the pump (which appears to be working) and then all stops.
The pressure is good.
Wondering if it is air in the system where it shouldn't be.
Any advice please.

Boiler problems - https://youtube.com/shorts/ppWEWP6HA7Q

 

[cjg]

could be sticking pump.pos on its way out.?

 

[Merton69]

could be sticking pump.pos on its way out.?

Thank you for replying.
How can I find out if it is on its way out?
I have removed the brass screw from the front and hot water does come out (after I have switched it on) and I have turned the impeller. It appears to be working.

Originally the problem was when switching the heating on, it would do as it shows in the video but when cutting out, the under pressure LED would eventually come on. That is not happening now.

 

[cjg]

ok try turning your ch temp to min see what happens,

 

[Merton69]

ok try turning your ch temp to min see what happens,

Thank you.
I have already tried turning it on with the temp at it's minimum. The same happens.
One thing I haven't mentioned is the temperature gauge goes quickly up to about 80, the clanking happens, then it all shuts down with the temperature obviously dropping as well.

 

[cjg]

then you have no flow\return i would guess pump gone,

 

[Merton69]

Thank you cjg.

As far as I can see, the pump is working.
Can I test the pump in any way to see if it is spinning?
Like I said previously, I can't undo the brass screw when it is on because the hot water squirts out very quickly and alot, to see if the pump is turning.

 

[cjg]

put a couple of towels down . undo srew , put flat screwdriver in it will hit the shaft inside that will let you know if its pump.

 

[Merton69]

put a couple of towels down . undo srew , put flat screwdriver in it will hit the shaft inside that will let you know if its pump.

WOW! Okay, I will see what I can do, but the amount of water squirting out is worrying, especially as it is very hot.

 

[cjg]

let it cool down first then try it