When water is heated the water will increase in volume. The thermal expansion tank in a boiler heating system is there to allow the extra volume of water some place to go. It also holds enough water to fill the void back up when the water cools.
The water expansion tank is a necessary item in heating systems. It also can cause problems if they do not work correctly. Some of the problems caused by a faulty expansion tank are:
- The boiler relief valve will be constantly dripping or blowing off if the tank is totally full of water and does not have the air cushion needed to counteract the increased volume of water as it is heated.
- Air can be introduced into the system if the tank does not hold sufficient volume of water to keep the system full as it cools.
- If fresh water is introduced into the system frequently the tank will rot out from the inside out.
One of the main things to remember is that a faulty boiler expansion tank
can make other things like the relief valve
look faulty when it reality it is not the problem. A bad expansion water tank
or a bad pressure reducing valve
can make the relief valve look bad. Or actually cause it to need replacement. Check everything out carefully before deciding what pieces need to be replaced. If go about just changing parts without a through investigation first you may be changing parts for a long time till you find the right one.