noisy boiler and pressure guage judders and goes upto 3.5?

you need to make sure your filling loop is turned off firstly. if its off and the pressure is constantly above 3 then your heat exchanger is probably burst allowing mains pressure into the heating system. if only when heating is on then expansion vessel probably needs re-pressurised. either way you're going to need a new pressure relief valve, that's what's making the noise.

Ian
October 2009