20
HOW A HOT WATER SYSTEM OPERATES
The entire heating system (boiler, piping, and
radiation units) is lled with water. As the water in
the boiler is heated, it is circulated from the top of
the boiler through the supply main to the radiation
units. The cooler water in the radiation units ows
back through the return piping through the return
main into the boiler. This arrangement provides
positive and rapid response to the thermostat.
FILLING THE SYSTEM WITH WATER
OPTION #1 This method utilizes the boiler piping
as shown in the gure on the previous page.
a) Close the main shutoff valve, isolation valves,
and zone valves (if applicable). If bypass pip-
ing is installed, also close the two throttling
valves. Leave the boiler service shutoff valve
(if installed) and the balancing valves to each
heating zone fully open.
b) Open the following valves in order: the drain
valve for power purging, isolating valves before
and after the boiler circulator (if applicable),
both throttling valves (if applicable), and then
open the ll line shutoff valve. Water will ll the
bypass piping and push the air through the
piping and out the power purging drain valve.
When the power purging drain valve runs air
free, close the bypass piping throttling valve
(leaving the throttling valve to the supply piping
fully open).
c) Next, open the isolation valve (or zone valve)
to the rst zone. Water will ll the piping and
push any air out the power purging drain valve.
When the power purging drain valve runs air
free, close the isolation valve or zone valve).
Repeat this procedure for the remaining heat-
ing zones.
FilliNg THe BOiler
d) Once all zones are lled with water and purged
of air, close the power purging drain valve and
ll line shut off valve, open the main shutoff
valve, and adjust the throttling valves and
balancing valves as required.
OPTION #2 Close the air vents on all radiation
units. Open the valves to the radiation units. Make
sure the boiler drain valve, expansion tank drain
cock, and the air bleed screw on the expansion
tank drain tting are closed. Open the ll valve on
the piping to the expansion tank. Open the water
inlet to the boiler and leave it open. Open the air
vent on the lowest radiation unit. When all the air
has escaped and water starts to ow from the
vent, close it. Go to the next radiation unit, and
repeat this process until nishing with the highest
radiation unit. If the heating system has automatic
vents, this manual venting is unnecessary but it
will speed up the proper lling of the system.
If the system is a closed expansion tank system,
an automatic ll valve is needed. Leave the auto-
matic ll valve open to rell the system automati-
cally as needed. Note the initial ll pressure on
the boiler’s temperature / pressure gauge, which
should be 10-15 psig. Any lowering of the pres-
sure from its initial ll pressure indicates a loss
of water due to leakage. The automatic ll valve
should then compensate for this water pressure
loss. If it does not, manually open this valve to
rell the system until the needle is again pointing
to the same pressure reading. Instructions are
packaged with the valve.
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