Are there any Vaillant boiler experts out there as we have found that the 2 Vaillant Engineers who have visited so far (plus Vaillant and the Plumber who fitted our boiler) do not have the knowledge to resolve the problem on their own boiler and seem to have put the issue down to 'my imagination'. A year later, the humming/buzzing/howling noise continues all night long when both water and heating is not in use and I have not had a decent night's sleep since this boiler was fitted. It seems impossible to pinpoint exactly where the noise is coming from. We have yet another Engineer visiting next week; recommended. Though we expect background noise whilst the heating and water are in use; we didn't expect the noise 247. A year of our guarantee is over already.