Honeywell T200 User Manual

11

62-3048—2

NOTE:

—

While the T100 is satisfied, the V2042H is closed 

and the radiator remains airlocked. Thus, no 

steam can enter the radiator. The airlocked 

condition remains until the T100 calls for heat, at 

which point the system operates as described in 

steps 1 through 6.

—

An improperly cycled boiler causes either 

excessive heating or lack of heat, depending on 

the system time constant.

To assure the proper operation of any single-pipe steam 

system, ensure that the steam pressure is brought to zero at 

some time during the off-cycle. One suggested procedure 

follows:

1. Determine if steam is required using one of two 

methods:

a. A thermostat in a representative zone controls the 

valve or cycles the boiler.

b. A timing device cycles the boiler for varying lengths 

of time in response to outdoor temperature.

2. Turn off the steam and allow system pressure to drop to 

zero. Do this using one of two methods:

a. Turn the boiler off and allow the total steam pressure 

in the system to drop to zero.

b. In installations where turning the boiler off at the end 

of each cycle is undesirable, install a control valve 

(such as a Honeywell V5011 Valve) on the boiler dis-

charge line.

NOTE: Install the valve on the boiler side of the condensation 

takeoff to ensure that the condensation can return to 

the boiler.

3. Verify that the steam pressure has returned to zero.

Verification is necessary to prove that the pressure has 

returned to zero. Simply turning off the boiler or shutting off the 

steam supply does not ensure zero steam pressure. The 

simplest way to check for zero pressure follows:

1. Install a strap-on Aquastat® Controller, such as the 

Honeywell L6006C Aquastat® Controller, on the 

condensation return line (see Fig. 19).

2. Set the Aquastat® Controller at about 150°F (66°C). 

With the return line at or below this temperature, the 

water is all condensation, and the pressure is 

functionally zero.

3. Wire the Aquastat Controller into the interrupting circuit 

to ensure that steam flow cannot resume until the 

condensation line is below the setpoint. The 150°F 

(66¡C) setpoint serves as a nominal starting point and 

can require adjustment for individual steam systems.

L1 

(HOT)

L2

1

1

LOW

VOLTAGE

RELAY

PRIMARY

CONTROL

24

Vac

L6006C

MASTER ZONE

THERMOSTAT

POWER SUPPLY.  PROVIDE DISCONNECT MEANS AND 

OVERLOAD PROTECTION AS REQUIRED.

M7536A