I have a radiator that is cold a the top and hot at the bottom. I therefore believe I need to bleed the radiator. I have a Glow Worm Compact 100e combi boiler. Do I bleed the radiator with the boiler on or off? My sister had a combi boiler at her last house and was left with no hot water (due to the boiler losing pressure) after she bled her radiators. I'd be grateful for any advice that means I won't be having a cold shower before going to work in the morning!