CAC / BDP BW4BAH-91, Installation, Operation & Maintenance Manual

19

How A Hot Water System Operates

Entire heating system (boiler, piping, and radiation units) 

is 

fi

 lled with water. As water in the boiler is heated, it 

is circulated from top of boiler through supply main to 

radiation units. Cooler water in radiation units 

fl

 ows back 

through return piping through 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 boiler piping as shown in 

fi

 gure on page 6.

A. Close

 main shutoff valve, isolation valves, and zone 

valves (if applicable). If bypass piping is installed, 

also close two throttling valves. Leave boiler service 

shutoff valve (if installed) and balancing valves to 

each heating zone 

fully open

.

B. Open

 following valves in order: drain valve for power 

purging, isolating valves before and after boiler 

circulator (if applicable), both throttling valves (if 

applicable), and then open 

fi

 ll line shutoff valve. Water 

will 

fi

 ll bypass piping and push air through piping and 

out power purging drain valve. When power purging 

drain valve runs air free, close bypass piping throttling 

valve (leaving throttling valve to supply piping fully 

open).

C. Next, 

open

 isolation valve (or zone valve) to 

fi

 rst 

zone. Water will 

fi

 ll piping and push any air out power 

purging drain valve. When power purging drain valve 

runs air free, close isolation valve or zone valve). 

Repeat this procedure for remaining heating zones.

D.  Once all zones are 

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 lled with water and purged of air, 

close

 power purging drain valve and 

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 ll line shut off 

valve,

 open

 main shutoff valve, and 

adjust

 throttling 

valves and balancing valves as required.

OPTION #2

• Close air vents on all radiation units. 
• Open valves to radiation units. Verify boiler drain 

valve, expansion tank drain cock, and air bleed screw 

on expansion tank drain 

fi

 tting are closed. 

• Open 

fi

 ll valve on piping to expansion tank. 

• Open water inlet to boiler and leave it open. 
• Open air vent on lowest radiation unit. 
• When all air has escaped and water starts to 

fl

 ow from 

vent, close it. 

• Go to next radiation unit, and repeat this process until 

fi

 nishing with highest radiation unit. 

• If heating system has automatic vents, this manual 

venting is unnecessary but it will speed up proper 

fi

 lling 

of the system.

If system is a closed expansion tank system, automatic 

fi

 ll 

valve is needed. Leave automatic 

fi

 ll valve open to re

fi

 ll 

system automatically as needed. 

Note initial 

fi

 ll pressure on boiler’s temperature / pressure 

gauge, which should be 10-15 psig. Any lowering of 

pressure from its initial 

fi

 ll pressure indicates loss of 

water due to leakage. Automatic 

fi

 ll valve should then 

compensate for this water pressure loss. If it does not, 

manually open this valve to re

fi

 ll system until needle is 

again pointing to same pressure reading. Instructions are 

packaged with valve.

FILLING THE BOILER