Most of the things that you will need to test your sealed central heating system for pressure variances are already built in. The water intake, pressure release valve, expansion tank, pressure gauge and discharge pipe should be installed on most heating systems already and vary only in their location throughout the home or the system.
Step 1 - Check Water Levels
Before taking a pressure reading of your sealed central heating system, you will want to do a few upkeep or maintenance tasks to ensure your reading is going to be accurate. At the cistern or feed tank where your cold water comes into the system, be sure that the water levels are set appropriately and add water as needed.
Step 2 - Raise Temperature
The next step in the process of testing the pressure in your sealed central heating system is to increase the boiler temperature just a few degrees and let it build pressure. Once a good core temperature is reached, check your lines and radiation for knocking or other off noises. This can be a sign of losing pressure in the lines.
Step 3 - Bleed the Lines
You then want to go to the radiators in your sealed central heating system and locate areas where hot and cold vary in the pipes. The areas that are cold do not have water in them and are holding air. The steam is hotter than the water up to a point, but it does not transfer the heat it is generating through the pipes very well, which is why you want to bleed the air out of the lines.
While your sealed central heating system is under temperature pressure use a pair of thick insulted rubber gloves to release this pressure from your release valves while your water intake is on. This will force new water into the system while the heated water expands in the pipes, increasing pressure towards your release valve. Once your release valve is pouring water, close the valve and wait to check for heat displacement in the radiation. The cold spots should vanish from the piping and become a solid temperature as you go along your system, one radiator unit at a time, bleeding and checking.
Step 4 - Check the Pressure Gauge
Once you have gone through and removed excess air from your sealed central heating system, turn off the water intake and turn down your boiler temperature to a standard setting to let the system build pressure for about 30 minutes. Once this time has passed your system should be equaled out and ready for a true pressure reading from the boiler.
On the working end of a sealed central heating system is the boiler, which can be fueled a number of ways, either by oil, wood or coal. It has a built-in water pressure gauge that sits near the boiler itself, as the water lines run on the inner walls of the boiler burner where the heat is generated and the hot water pressure starts to build.