hermann supermicra he24 gas burner on and off every 5 seconds on ch or dhw

[julesverne]

hi could anybody point in the right direction and i'm at bit stuck on this.

hermann boiler supermicra 24 he fires up on and off every few seconds constantly when boiler is on , this is either ch or dhw, only noticeable on dhw as it is not sufficient to warm it up. ch gets to temp eventually with it being a closed circuit, does anyone have any idea what it could be.

any help would be most appreciated

thanks julian