Hi, drained a central heating vented system today to fit a new rad valve, turned the cold water back on and restarted system, boiler tripped (Worcester greenstar ri) sounded really rough as though there was air in, tried to bleed radiators but no water, checked cold supply and tank was full but would not drain, suspected blockage in cold feed, used hose pipe to push water back through system until water came out in breather above tank, then blocked this and water then came up cold feed into tank so clearing blockage, managed to bleed radiators ok but now can't get boiler to stay on, keeps cutting out after approx 1 min of running. Think i have done some damage to the boiler, Can anyone help?

Gary, October 2011

After draining the central heating system, it is necessary to bleed the heat exchanger in the actual boiler. If you look in the technical manual that was provided to you (hopefully) when the new bolier was installed, you will find a section about how to start up the system. You need to take considerable care to shield off the electrical parts, like the fan and other connevctions with strong platic sheet when bleeding the valve at the top of the heat exchanger because water will come out at the base of the plastic nut which forms part of the bleed valve mechanism, as well as coming out of the short hose. Have a smallish bucket tied up just below the bottom end of the hose in the boiler to catch the drained water. I must warn you that you might have to repeat the process four of five times before the air in the boiler clears. BTW, you will need to remove the outer cover of the boiler to do this,od course! Two screws at the bottom, angled slightly upwards and two small grub screws at the top of boiler. If you don't fancy all this , I suggest you call in a 'Corgi fitter to bleed the boiler. Worcester-Bosch Technical support do not encourage home owners to do this procedure, I have found! Good luck, and be patient!

Graham, October 2011

no damage should have to the boiler, may be sluged or scale in heatexchanger thus poor circulelation may be the cause

k, October 2011