What do boiler relief valves protect against? High system pressure. Boilers and equipment are rated to a certain pressure rating. Pressure in a boiler system comes from water expanding as it is being heated by the boiler. This is the reason for the expanison tank. As pressure rises it pushes against the air filled bladder. and then pushes in to the empty part of the container. If the tank is full of water it will blow the valve.

Boiler relief valves blow or weep for typically 2 reasons:

1: Expansion Tank is water logged

2: Pressure in system is rising due to some input

Expansion Tanks should be set properly to provide enough room for expansion of water in the system. Here is a quick guide.

Get a hold of out design team for expansion tank sizing. [email protected]

The other reason is because water is being introduced into the system. Look at your fill valve. Try to shut off supply to boiler and you will see the pressure stop rising.