Jessie, Not sure I agree with you when you say that injectors working correctly 'sing' as this indicates that air is being sucked in the overflow and = pumped into the boiler at the same time as water. I believe that when working = at its optimum there should be the slightest trace, just a bubble of water issuing from the overflow. Regards IP Priest & Sons Model Engineers http://www.kinvermes.pwp.blueyonder.co.uk/p1.htm Version: 7.0.308 / Virus Database: 266.7.4 - Release Date: 18/03/2005 =20 --=20 No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.308 / Virus Database: 266.7.4 - Release Date: 18/03/2005 =20 MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.