Service; Gas Pressure - Mr. Heater MHU 50 Operating Instructions And Owner's Manual

TABLE 4
NATURAL GAS MANIFOLD PRESSURES - IN.WG. (KPA)
MHU 50/80
50/80 4.0"WC (0.99 kPa)*
*No adjustment required.
TABLE 5
LP/PROPANE GAS MANIFOLD PRESSURES - IN.WG. (KPA)
MHU 50/80
50/80 10.5"WC (2.62 kPa)* 8.5"WC (2.12 kPa)
*No adjustment required.
GAS FLOW
To check for proper gas flow to the combustion chamber,
determine the Btu input from the appliance rating plate. Divide
this input rating by the Btu per cubic feet of available gas. Result
is the required number of cubic feet per hour. Determine the flow
of gas through the gas meter for two minutes and multiply by 30
to get the hourly flow of gas.

GAS PRESSURE

1. Check gas line pressure with unit firing at maximum rate. A
minimum of 5.0" w.c. for natural gas or 10.9" w.c. for LP/
propane gas should be maintained for proper unit operation.
2. After line pressure has been checked and adjusted, check
manifold pressure. Correct manifold pressure is shown on the
unit rating plate. See figure 10 for gas pressure adjustment
screw location. A natural gas to LP/propane gas changeover
kit is required to convert unit. Refer to installation instructions
provided with changeover kit for conversion procedure.

SERVICE

CAUTION Turn off gas and electrical power to unit before
performing any maintenance or service operations on this unit.
Remember to follow lighting instructions when putting unit back
into operation after service or maintenance.
If any of the original wire as supplied with the appliance must
be replaced, it must be replaced with wiring material having a
temperature rating of at least 105°C. Do not use this appliance
if any part has been under water. Immediately call a qualified
service technician to inspect the appliance and replace any gas
control which has been under water.
BURNERS
1. Periodically examine burner flames for proper appearance
during the heating season.
2. Before each heating season examine the burners for any
deposits or blockage that may have occurred.
3. Clean burners as follows:
ALTITUDE FT. (M)
0-2000 2000-4500
(0-610) (610-1370)
3.6"WC (0.89 kPa)
ALTITUDE FT. (M)
0-2000 2000-4500
(0-610) (610-1370)
Compact Unit / Utility Heater
• Turn off both electrical and gas supplies to unit.
Disconnect gas supply piping, high tension and sensor
•
leads. Remove gas manifold. Remove burner tray.
Clean burners as necessary. Make sure that burner
•
heads line up properly to ensure flame crossover.
Check spark gap on electrode and adjust if required.
The gap should be between 0.110 inch and 0.140 inch
(2.79mm to 3.56mm). The gap may be checked with
appropriately sized twist drills or feeler gauges.
Reinstall burner tray, gas manifold, high tension and
•
sensor leads. Reconnect gas supply piping.
Restore electrical power and gas supply. Follow lighting
•
instructions to light unit. Check burner flame.
FLUE PASSAGEWAY AND FLUE BOX
The flue passages and flue box should be inspected and cleaned
prior to each heating season. The sequence of operation should
be as follows:
1. Turn off both electrical and gas supply to unit.
2. Disconnect combustion air blower wiring.
3. Remove screws securing flue box to unit. Remove flue box. If
necessary, remove blower assembly from flue box. Clean flue
box with wire brush.
4. Remove turbulator retention bracket and turbulators. Clean
turbulators with wire brush.
5. Remove burners as described in section "BURNERS" section.
6. Clean tubes with a wire brush.
7. Reassemble unit. The combustion air and flue box gaskets
should also be replaced during reassembly.
8. Restore electrical power and gas supply. Follow lighting
instructions to light unit. Check operation of unit.
COMBUSTION AIR BLOWER
Under normal operating conditions, the combustion air blower
should be checked and cleaned prior to the heating season with the
power supply disconnected. Use a small brush to clean blower wheel.
ELECTRICAL
1. Check all wiring for loose connections.
2. Check for correct voltage at unit (unit operating).
3. Check amperage draw.
FLUE AND CHIMNEY
Check all vent and vent connector joints for tightness. Ensure that
connections are sealed and that there are no blockages.
FAILURE TO OPERATE
If unit fails to operate check the following:
1. Is thermostat calling for heat?
2. Is main disconnect closed?
3. Is there a breaker tripped or a fuse blown?
4. Is gas turned on at meter?
5. Is manual shutoff valve open?
6. Is unit ignition system in lock out? If unit locks out again, call
service technician to inspect unit.
7. Is pressure switch closed? Obstructed flue will cause unit to
shut off at pressure switch. Check flue passage and outlet.
12
Operating Instructions and Owner's Manual