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FAILURE TO PROPERLY SEAL WILL RESULT IN LOSS 

OF PRECHARGE CAUSING PRODUCT TO FAIL

.

Installation

THIS PRODUCT MUST BE INSTALLED BY A 

LICENSED PROFESSIONAL.

1. Visually inspect THERM-X-TROL

 

for any damage. If damage 

exists return product for replacement.

2. Adjust pre-charge to equal incoming pressure.

IMPORTANT

: If increasing pre-charge pressure above 

55 psig the following steps must be followed:

a. Tank must be connected to the system with isolation 

valve open.

b. System must be pressurized to 55-60 psig or slightly 

higher than the pre-charge setting of the tank.

c. Isolation valve needs to be shut.
d. Pre-charge pressure of tank can now be increased to 

the recommended high pressure setting.

e. Bring system up to pressure, and then open the 

isolation valve to the tank.

Failure to follow these steps could result in damage to 

the bladder and void all warranties.

3. Replace and tighten plastic cap on air fitting.

4.  Install the THERM-X-TROL

 

on the city supply line to the 

water heater at a point between the water heater and 

backflow preventer, check valve or pressure reducing valve 

(see Figure 1).

5.  Once the THERM-X-TROL

 

 is installed, check the city supply 

line for any leakage. Make repairs if necessary.

6.  Before the initial firing of the water heater, open any hot 

water fixture and draw water until all air is removed from the 

system. Turn the water heater temperature control to desired 

ending temperature level, (see water heater instructions).

7.  To relieve initial thermal expansion, slightly open a hot water 

faucet. Continue until water heater aquastat temperature is 

satisfied. Once heater is at its operating range, no further 

bleeding of expanded water is required.

8.  The system water heater and THERM-X-TROL

 

will now 

be operational.  The THERM-X-TROL

 

will control pressure 

increases caused by thermal expansion to a level well below 

the water heater relief valve setting.

Maintenance

1.  A licensed professional should check the complete heating 

system, including the THERM-X-TROL, yearly and more 

frequently as the system ages.

Operation

1.  The THERM-X-TROL

 

 is installed in the supply line between 

the backflow preventer and the water heater. Its sealed-in air 

pre-charge prevents water from entering it until the system 

pressure exceeds the pre-charge pressure.

2.  As the water temperature rises, expanded water enters 

the THERM-X-TROL’s non-corrosive water reservoir. The 

pre-charged air chamber absorbs the pressure increase, 

keeping system pressures below the relief valve setting.

3.  As hot water is used, the pressure in the air chamber forces 

water back into the system until the THERM-X-TROL is 

empty. At this point, the pressure in the air chamber once 

again equals the supply pressure.

4.  Water treatment is not to exceed 200° F or fall below 35° F.

Warranty

ST-35L(CL) through ST-600L(CL) Models:  

One (1) Year Limited Warranty

Visit www.amtrol.com for complete warranty details.

PLEASE READ THE FOLLOWING INSTRUCTIONS CAREFULLY

IMPORTANT GENERAL SAFETY INFORMATION - 

ADDITIONAL SPECIFIC SAFETY ALERTS APPEAR IN THE FOLLOWING INSTRUCTIONS.

Hot Water

CWS

Water

Heater

Back Flow Preventer

Check Valve or

Pressure Reducing Valve

Air Valve

System

Connection

bladder

THERM-X-TROL

Lifting

Ring

Figure 1.

© 2019 Worthington Industries Inc. 

Part #: 9017-118 (06/19)

One or more features of this product are covered by U.S. patents, visit www.amtrol.com/patents for more information. 

1400 Division Road, West Warwick, RI  USA 02893

T: 800.426.8765  

www.amtrol.com

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