Ariston Microgenus Problem

[whitefox723]

Hi

My Ariston boiler is playing up.When I run the CH i cannot run it on min or 1,it has to be 2 or 3+.If I run it on 1 the boiler is noisy as though the burner is constantly trying to ignite,if i turn it up to 2 this then rectifies the problem.
If I run on 3 then turn down to 2 the same thing happens and then if I open the hot water tap for a bit then switch off it will then happily run on 2 without the burner attempting to kick in.
Any ideas because running it on 2 or 3 is using more gas. B.Gas serviced it last year and found no problems on read outs?

Thanks

 

[twgas]

sounds like its heating up too quickly, could be anything from burner settings to pump being on its way out.
whats the actual perfermance like - do you get CH and HW when demanded

 

[whitefox723]

sounds like its heating up too quickly, could be anything from burner settings to pump being on its way out.
whats the actual perfermance like - do you get CH and HW when demanded

Yes CH and hot water are fine,just this burner noise.Also pressure when not running is 1bar,is that normal.Tried adjusting filling loop but can't free plastic keys