After having the heating on and it has been switched off, water blows out of the overflow. It then needs to be topped back up before starting the heating.Is the problem the expansion vessel? The model is a VCW -sine 18T3W.

Ken Wooldridge, October 2008

yes you can check this with a foot pump or tyre pressure guage. release all the pressure from your c/h system and locate the shraeder type valve on the expansion vessel. the pressure should read 1bar.if it isnt pump this up to one bar with a foot pump and you should hear the water being forced out of the vessell remember to leave the drain valve open when doing this or you will get a false reading ,normally it will take up to 50 pumps to repressurise this.refill the heating as normall and it should be ok.If you cant get any pressure in it or it goes back to zero in a couple of days you will need to have it replaced and on that boiler its not worth it have the boiler replaced.

stevie w, October 2008