LAARS Mighty Therm VW (Sizes 2000-5000) - Installation, Operation and Maintenance Instructions - Manual (Page 15)

Page 15 Mighty Therm Volume Water Heaters
3. Heater will not fire.
A. Electric power is off.
B. Operating or safety control
has opened circuit to electric
gas valve.
C. Pilot flame is out.
D. Manual reset device has
tripped.
E. No gas pressure to burners.
F. Electric gas valve operator
is burned out or shortened.
Possible Cause What To Do
A. Check to see that main power
switch is “ON.” Use testing
device to trace power to
heater junction box.
B. Turn off power. Use continuity
across terminals of each
operating and safety control
switch up to the electric gas
valve. Replace effective
control.
C. Relight pilot per instruction.
D. Follow instructions for start-
up. Reset pilot safety and all
manual reset safety switches
and reset manual safety gas
valve.
E. Trace gas line to service
shut-off cock. If service cock
is open, trace gas line to
meter. If no pressure is
present at meter, call for
public utility service. If gas is
present in heater inlet, check
pressures in following
sequence: (1) downstream
from pressure regulator. (2)
downstream from electric gas
valve. Replace or adjust as
necessary.
F. Disconnect wiring harness at
gas valve terminals. Check
continuity to actuator coil. If
open circuit or short is
indicated, replace coil or
operator.
5. Heater is pounding, knocking or emitting steam
from relief valves.
Possible Cause What To Do
A. Low or no water flow.
B. Low or no system
pressure.
C. Clogged “Y” strainer.
D. Debris from system piping
is blocking tubes.
E. Scale has formed in tubes.
A. This condition is usually
caused by lack of adequate
water flow through heater.
Check the following:
1. Is the heater wired into
the pump circuit so that the
heater cannot fire unless the
pump is running?
2. Check to see that all
valves system are open to
be sure that water can
circulate through the heater
and the system.
3. If the system has
automatic water valves (2-
way or 3-way) that can cut
off the water flow through
the heater; check to see that
they are equipped with end-
switches which shut the
heater down when the water
flow through the heater is
reduced by 70% from full
flow.
4. Examine pump for
clogged impeller.
B. Clean strainer in pressure
reducing valve. Look for
closed valve water line or a
leak in the system.
C. Remove strainer element
and clean screen.
D. Remove header covers.
Examine all tubes and
waterways. Use new
gaskets when reassembling.
Clean out tubes.
E. This is always caused by the
inflow of raw water into the
system. Clean tubes with
tube cleaning kit. Determine
hardness. Check water flow,
replace pump for modified
flow if necessary.
Possible Cause What To Do
4. Pressure relief valves leaking intermittently or
steadily.
A. Static pressure in system
exceeds setting of relief
valve.
B. Expansion tank is
waterlogged (if installed).
A. Calculate height of water in
system above heater. Install
new valve with psi setting
25% above required static
system working pressure.
Do not exceed 160 psi.
B. Drain expansion tank, then
reopen it to the system.
Look for leaks in expansion
tank or fittings. Calculate
required volume of
expansion tank in relation to
system to determine that
tank is adequate.