Natco VW Installation And Operating Instructions Manual page 22

I. HEATER WILL NOT FIRE
Possible Cause
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.
III. PRESSURE RELIEF VALVES LEAKING
INTERMITTENTLY OR STEADILY
Possible Cause
A. Static pressure in system
exceeds setting of relief valve.
B. Expansion tank is waterlogged
(if installed).
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 shutoff
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.
What To Do
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.
II. HEATER IS POUNDING, KNOCKING OR
EMITTING STEAM FROM RELIEF VALVES.
Possible Cause
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.
22
What To Do
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
in 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.
Examinie all tubes and water-
ways. 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 hard-
ness. Check water flow, replace
pump for modified flow if
necessary.