Therma Grow™ Greenhouse Heaters
Owner’s Manual • Therma Grow™
19
Air Proving Switch
1. Remove two sheet metal screws holding air proving
switch blower housing. Remove assembly by
turning switch assembly 90 degrees so the switch
paddle can be pulled through oblong hole on side of
fan housing. See Fig. 13.
2. Disconnect the leads from the air proving switch.
3. Use care when installing the replacement switch
(includes cover bracket), to prevent bending of
switch arm which may create ignition problems.
FIG. 13
High Limit Switch
The high limit switch should be tested a minimum of
once per year when the heater is given a thorough
cleaning.
1. Remove the high limit switch from the heat
chamber.
2. Holding the switch by one of its mounting legs or
electrical terminals, apply a
small
flame only to the
sensing surface on the back of the switch.
Be care-
ful not to melt the plastic housing of the switch
when conducting this test.
3. Within a minute, you should hear a pop coming
from the switch, which indicates the contacts of the
switch have opened.
WARNING
Fire Hazard
■ Do not operate the heater with the high limit
switch bypassed.
■ Operating the heater with a bypassed high limit
switch may lead to overheating, possibly result-
ing in a fire, with subsequent damage to the
heater, building damage, or loss of livestock.
4. Allow the switch cool down for about a minute
before firmly pressing the red reset button on
the switch.
5. Check for electrical continuity across the switch
terminals to make sure the contacts have
closed.
6. Reinstall the switch back into the heater.
FIG. 14
Gas Control Valve
1. Remove the following
-- Hose and sediment trap from inlet of gas valve
-- Screws securing valve bracket to heater base.
-- Burner bolt from underside of base.
-- Screws and spacers securing burner casting to
heat chamber.
2. Remove control valve with burner from heater.
Turn the valve/manifold assembly as necessary
so orifice block on manifold can be pulled from
the burner casting venturi port..
3. Replace components as needed.
FIG. 15A
Therma Grow 220 Models
ORIFICE
BLOCK
ORIFICE
GAS VALVE