Where does the water go?

Rav

Here's a question from a newbie to HVAC (me).



My house was built in 1931 (if that matters).  I have a gas-fired hot water (not steam) heating system.  The boiler is a Weil-McLain series 8 CGM-5, with black pipes leading to the radiators upstairs.  I know there's a water supply to the boiler (the line with a pressure reducer and backflow preventer).  But other than someone manually draining water from the system for whatever reason, why does the system need a continuing source of water?  I thought the "system" was sealed, so if water is lost, where is it going?  Thanks.

Gordy

Hydronics

Your system is sealed unless there is a leak, or its drained to do work on it.

 There is an automatic water feed (PRV) that if the system goes below 12 psi it will allow water to replenish to bring up to 12 psi so long as the supply valve is open. Or what ever psi your system needs by setting the PRV. Most residential systems are 12 psi.



 Gordy

Mark Eatherton

are you SURE you're losing water???

If you turn the make up water valve to the OFF position, and your pressure stays stable, you don't have a leak. If the pressure does drop, start looking for a leak, and it can be below the basement floor (if there are any pipes there) or it could also only leak water when the boiler is running. That would be evidenced by significant steam in the exhaust plume, even when it is not all that cold outside.



It was (still is) common place to have an automatic make up on most closed hydronic heating systems. If you have a low water fuel cut off, you can safely turn the make up off. If not, I'd recommend you get one any way. Cheap insurance against catastrophic damages...



ME

Rav

Our system doesn't actually have a leak

(as far as I know).  It was just a question to understand why there's an automatic water feed if a system is running normally (not leaking).  It sounds like it's more of a safety thing, i.e. if there WAS a leak, it would feed more water to make it up.

Mark Eatherton

Belt, no suspenders...

There have been numerous cases of people leaving the make up to their boilers on, and for whatever reason, the city turned the water to a city block off, and the boiler had a leak below the floor, and the boiler ran dry, and the thermostat called for heat and dry fired the boiler, and when the city turned the water back on again, KABLOOEY, the dry fired, cherry red glowing boiler gets hit with water and explodes.



I have personally walked into one of these situations, and it made my sphincter do the momba. I left the power to the boiler on, then carefully backed out of the boiler room and RAN outside and turned the gas off, allowing the boiler to cool off by itself. Turning off the electrical power to the boiler can cause a catastrophic explosion if the circulator is holding water away from the red hot boiler, and when shut off, the pump allows water to flow back to the cherry red boiler, causing a steam explosion.



I prefer belts WITH suspenders. I set my systems up with a captive make up that compensates for the oxygen removal upon a major drain and refill, and then install a low PRESSURE cut out (you will lose pressure before the boiler goes dry) AND a low WATER cut off. I leave the make up off to avoid any potential major water damage should a pipe or something break when no one is home.



Can never be too safe when dealing with flames, and water, and electricity, and explosive potentials...



ME