Your plumber or heating engineer should have that taken care of for you. Check the pressure gauge. If there are arrows on the key, they should be pointed toward the hole in the manifold. After turning your boiler off, wait a few hours so it can cool. Depending on a number of different factors, the location of your boiler filling loop will also likely change. Ones that cater to professional plumbers and heating engineers are bound to have stock ready. By keeping the pressure at the proper range, you not only get an efficient boiler, but you also minimise the damage on your pipes. A system boiler heats a hot water tank to give you hot water. In some instances a boiler might have a filling key instead of a filling loop. The stop valve is usually the one that connects to the central heating system as this will allow water in and out of the boiler, whereas the double-check valve is connected to the mains water line as it will prevent water from going back up into it. System boilers, for example, will have external filling loops, but will again likely be accessible at the underside of the boiler, likely looking like a pipe amongst other pipework. First, fully open the cold water mains valve and then the heating system one. Registered in England No. Bosch Thermotechnology Ltd, Registered Office Address- Cotswold Way, Warndon, Worcester, WR4 9SW Company registration number in England 1993294. {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/b\/bf\/Repressurize-a-Boiler-Step-1.jpg\/v4-460px-Repressurize-a-Boiler-Step-1.jpg","bigUrl":"\/images\/thumb\/b\/bf\/Repressurize-a-Boiler-Step-1.jpg\/aid9295602-v4-728px-Repressurize-a-Boiler-Step-1.jpg","smallWidth":460,"smallHeight":345,"bigWidth":728,"bigHeight":546,"licensing":"