Ariston Eurocombi a23/MFFI noise

[burgensteen]

Hi, My boiler (ariston Eurocombi a23.mffi) is making a LOUD drilling noise I have had an engineer out who said it was the gas valve but then didn't want to come back and change it. Then I have had another engineer out who said it was the gas valve so he changed it (dind't fix the problem) so then he changed the PCB (the one that has the control knobs on it) but this didn't fix the problem.
Could it be the main PCB (the one that is fed by the 240v mains supply).

I know I could get a new boiler but at present with the covid19 lockdown I really dont want an engineer in the house all day lifing boards, fitting boiler, fitting new flu, etc.

Thanks for any constructive advice you could give.

 

[hard-work]

When does it make the noises?

 

[burgensteen]

Hi,
It makes the noise whenever hot water is run or the burner is on for the heating.

Hot water - permanent
Heating - every 10 seconds or so whenever the burners ignite.

 

[hard-work]

Did they look at the fan?

 

[burgensteen]

No they didn't. This has been a real pain to sort.
3 engineers I rang arranged a time to visit but didn't turn up, One engineer turned up, diagnosed the gas valve the didn't return or call. Last engineer seemed brilliant. He took the boiler to pieces just about and diagnosed the gas valve or PCB (but thoght it was the gas valve) He said it modulates and it was when it was on the high setting it makes the noise (he pulled a wire off the gas valve to make it go in to low setting and the noise stopped).
If I put the boiler into flu test mode the burners burn full and there is no noise but when I put it back in to summer or winter mode the noise comes back when the burner ignites. If I hold the bottom of the gas valve (the bit with the two wires going in and a red screw under a clear plastic cover) it muffles the nolise slightly.

Sorry for my lack of knowledge when it comes to boiler terminology but I really appreciate that you are taking the time to help as the thought of having a boiler replacement during Covid19 scares me.