Pressure issues with your boiler can be dangerous. Overly high pressure can lead to an explosive burst, which can lead to major home damage or even injuries to anyone nearby. Low pressure is not dangerous, but it will prevent your boiler from working properly. The following are some of the most common reasons why a boiler begins to suffer pressure issues.
A failing thermostat can lead to overheated water, which causes the pressure to climb to dangerous levels. If the temperature gets too high, water and steam will move into the expansion tank. Once this safety tank reaches capacity, the boiler may begin to leak. In extreme cases, it can burst with explosive force. On the other hand, if the thermostat fails in a manner that leads to reduced heating, the pressure will drop and the boiler won't work properly.
Pressure Valve Failure
Every boiler is equipped with a pressure relief valve. This valve is supposed to open in the event the pressure in the tank gets too high. If the valve drips moisture occasionally, then it is working properly and there is no need to worry. Every boiler is equipped with a drain tray beneath the pressure relief valve to prevent water damage from occurring when the valve is in operation. The valve has failed and it needs to be replaced if your boiler is showing low pressure but water is dripping from the relief valve. If the pressure reads high and there is no water coming from the valve, then the pressure relief valve is malfunctioning and it must be replaced immediately for safety reasons. Turn off the boiler until the valve can be assessed and repaired.
Low pressure isn't always the result of a failed relief valve or thermostat. If the boiler tank has developed a leak, then there may be too little water inside the boiler for proper pressure to build up inside. Leaks should be easy to spot since there will be water around the base of the boiler or collected in the drip pan below it. Leaks that occur at hose inlets or valves can typically be repaired, but a crack in the boiler tank will likely require a replacement unit.
Conversely, if there is too much water in the boiler system, then the pressure can reach dangerously high levels. Fortunately, this is usually an easy fix. You can bleed the extra water out of the radiators. Every radiator should be equipped with a safety valve, which will drain the excess water once opened. Use caution since the water will be hot, and make sure you have a bucket on had to catch the drained water.
Contact a plumbing or HVAC professional if you are having issues with the pressure inside your boiler.