Hot water boiler...

[mrcaptainbob]

How does it work? I have a Utica Boiler model MGB125HD rev B. There are four zones to it. I understand how the propane flame heats the water and then it gets pumped to whichever zonevalve opens. My questions are:
Is the main 'tank' always kept at the 174/180 mark so when a wall thermostat calls for heat it opens a valve and turns on the pump and it's good to go?
Is there a separate temperature sensor for the boiler unit?
There's a large (what looks like cast iron) device imprinted with "air-sep" on the side. Does that automatically separate any air from the water?
On top of "air-sep" there's a device with what appears to be an air valve. The device says "40#'s psi max. But there was a metal cap on it with a rubber washer. I removed the cap and it hissed as if to relieve pressure. Did I screw it up? What does that unit do?
Under what appears to be an air tank, there's an air-valve with a screw-on plastic protector. What does that valve do?
I had to drain the boiler unit recently. After reconnecting it I turned the fill valve to accomplish that. Is there a method to bleed the air from the system between the two shutoff valves?
I flipped the switch arm on the pressure/temp relief valve. Now there's a bit of minor drippage. Did I do wrong in messing with that flip lever? Shall I replace it?
THanks in advance for your help.....

[LazyPup]

On a hydronic system the boiler temperature is constantly regulated by a thermostat on the boiler in the same manner as a water heater.

The individual zone thermostates then control the zone valve and circulating pump for that specific zone.

The tank that you are describing as an air tank is probably a rubber bladder type expansion tank.

Water is at maximum density at 40deg.F and if heated or cooled from that point water expands. The rate of expansion is fairly great which accounts for why water pipes burst when they freeze.

The solenoid valves used to control the zones are also quick acting valves which tend to enhance water hammer effecting on a piping system.

To compensate for water hammer or thermal expansion an expansion tank is installed on the system.

In its simplest form an expansion tank or water hammer arrestor is simply an inverted vessel that traps air in the top section. Water will not contract, whereas the trapped air can contract or expand to maintain equilibrium with the water pressure. When an expansion tank is made of steel there is a problem with the inside of the tank being constantly wet from the water and in contact with a source of oxygen from the air which results in rust on the internal tank walls. To prevent rusting modern expansion tanks have a rubber bladder to contain the air.

Most municipal water supplies or well pump systems are regulated to provide approximately 40psi line pressure, so the bladder is charged with 40psi air pressure to compensate for water supply pressure. During operation if the water pressure should increase from either expansion or water hammer the air in the bladder will compress to absorb shock thus protecting the piping system.

Sight unseen it is difficult to know what the Air-SEp is but I would guess you are correct that it is an automatic air separator trap.

The pressure/temperature relief valve (T&P valve) is basically the same type of valve as those found on water heaters.

T&P valve specifications say they should be manually opened once per year during tank maintenance. One of the common problems that occurs, especially in conditions of hard water is that the valve and vale seat s become coated with mineral deposits. Often when the valve handle is lifted, the valve opens and a bit of the sediment scale buildup becomes dislodged and ends up on the valve seat, which then prevents the valve from fully closing and resulting in a minor weep type leak such as you describe.

You may try lifting the valve handle and letting is snap back down a couple times to see if it will clear the seat and stop the leak. If not, replace the valve.

If it is necessary to replace the valve check the disharge port size and BTU rating that is stamped on a metal tag on the vavle handle. It is vitally important that the replacement valve be matched to the BTU rating of the heat source. (This is important on both boilers and water heaters.)

Also, check the diameter of the discharge line from the T&P valve. The line diameter must be equal too or greater than the diameter of the valve discharge port. Under no circumstances should that line ever be down sized. Even a slight downsizing of the line can critically effect the valves ability to relieve pressure, by example, most water heater T&P discharge ports are 3/4 inch. People commonly make the mistake of installing a reducer and using 1/2inch copper for the discharge valve line.

The capacity of a line is determined by cross sectional area rather than diameter, and a 1/2inch line only has 1/2 the capacity of a 3/4inch line, thus by downsizing the discharge line from 3/4 to 1/2 inch copper reduces the valves relief capacity to 1/2 of its rating.

[imeduc]

The pressure/temperature relief valve (T&P valve) is basically the same type of valve as those found on water heaters
I think if you check here they are different . the T/P on a water heater is like said by BTU . But with a 210o F relief and a 150psi.
Where as on a boiler the pressure relief valve is in with the auto fill on the boiler most of the time . This will go off at 30 lb psi.
That 180o for temp is good and your Psi for one floor should be 15 to 18 psi

ED

My mistakes dont define me they inform me.

[mrcaptainbob]

Thanks for that info. It confirmed my suspicions. I did snap that T/P valve a few times and did let some water through. It's fine now. And the info on the boiler thermostat was also very helpful.