disconnecting gravity hot water radiator

Mike T., Swampeast MO

The pressure reducing valve (thing that looks like a regulator/relief) is working against you. Close all the bleed valves and air pressure in the system builds (it can't tell the difference between air/water) and filling slows to an absolute crawl as it nears setting (usually around 12#).

Look for a "fast fill" bypass line around the pressure reducing valve. Open the valve in the line if you see it--but make CERTAIN you have air bleeders open or you'll pop the T&P valve at the boiler! Once the systems nears full, close the fast fill valve and let the PRV take over.

If you don't find the bypass, you must still open bleeders.

Possible to do this one-by-one for each radiator, but you'll be there a LONG time. With two or more people things to MUCH faster. Tin cans hanging from the air bleeds come in VERY handy to help prevent "accidents".

A. Blake Cooper

I have been tasked with laying some flooring at a relatives house. The house is circa 1890's with a gravity hot water system. I need to temporarily disconnect a radiator for the job, but I'm not sure of the proper method to do this. I know nothing about gravity hot water, but have the notion that the system is full of water and works based on convection. There is a valve on the inlet and a straight pipe into the wall on the outlet. Any advice is appreciated.

Al Letellier

gravity water system

Sorry, but you have to drain the system to at least below that radiator. You seldom if ever see isolation valves on that kind of system, and that valve at the rad will only stop flow, so drain away. When you refill, you'll have to vent all the rads. Do it cold first and then heat them up and revent. Good luck.

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A. Blake Cooper

refilling gravity hot water

Well I drained the entire system, went to disconnect the rad. Loosened the union on the valve then went to unhook the return and surprise there's no union. Didn't have the time to mess around with cutting in a union, so I did the floor and pieced in the radiator....

Now I've started to fill the system... I closed the valve which feeds the expansion tank, the tank looks like a large steel tank. I'm not sure what special things need to happen with that. The city water supply into the boiler has what looks to be a regulator/relief combination on it. The flow into the boiler doesn't appear to be very great based on the amount of time it has taken to get water just to the radiator vent level of the first floor.

At this point I have water coming out the vents of all the first floor rads. I've yet to get a second floor rad filled. Initially the air pressure is built up when I open the vent, but it fades eventually to just a small breeze and I feel like I'm waiting there endlessly waiting.

Any advice on properly filling and getting things working again would be great. I already wish this system was steam.

A. Blake Cooper

Can you offer any advice on the expansion tank deal? It's in the basement above the boiler. There is a valve inline, which I have shut at the moment. I would think that once I open that valve the tank would just fill with water and leave no expansion space.

Mike T., Swampeast MO

The tank is closed so as water enters from the bottom it compresses the air above. No place for the air to leave the tank because it can't travel back though the water (when filling at least). When properly sized, the old plain tanks wind up about half filled with water.

IF you see a strange looking fitting (usually red) on the bottom of the expansion tank it's most likely a B&G air-trol. In that event:

Re-drain the system completely. Close ALL bleeders EXCEPT that at the bottom of the air-trol. Fill until a clear stream of water runs from the air-trol. Then open the radiator vents and fill system to 12#.

If no air-trol and if you closed the valve BEFORE you drained and it has remained closed EVER since you can fill the system to 12#.

If you closed the valve AFTER you drained (or have opened it since), you need to completely drain the system and re-fill. Leave the valve to the tank OPEN when you fill. Again, the water will rise into the tank but since the air can't leave it will become pressurized and as long as the tank is tight it will wind up with both water and air inside.

REGARDLESS of the situation it's a VERY good idea on a gravity conversion to run the circulator continually for a day or two--easiest way is usually to disable the boiler main burner (set gas valve to pilot) and turn the t-stat way up. Then bleed the radiation--you're almost certain to bleed air from some of the radiators. If you seem to get a lot of air, keep the circulator running another couple of days.

If you'd closed the valve to the expansion tank BEFORE draining, run the circulator and bleed BEFORE you open the valve.