LAARS Mighty Therm LO-NOx VW (Sizes 250/400) - Installation, Operation and Maintenance Instructions - Manual (Page 23)

Mighty Therm LO-NOx Volume Water Heater Page 23
7. Tighten the header bolts progressively, starting
with the two center bolts. Maximum torque is 20
inch pounds (27 Nm). Do not over-torque.
8. Pressure test the heat exchanger for leaks with
city water supply before re-installing.
9. When placing the heat exchanger back in the
heater, carefully hold the refractory insulation
blocks apart and lower the heat exchanger into
place. Be sure the sheet metal covers, which
protect the insulation blocks, are replaced
carefully.
10. If a header bolt is stripped, drive it out of the
header plate and replace it (see Section 6, Parts
List).
11. Reinstall the heat exchanger.
SECTION 5.
Troubleshooting and Service
5.1 Gas Pressure Tests
Use the following procedures to check the main
gas supply and manifold gas pressures. A manometer
kit is available from Laars and instructions for its use
are included in the kit. A dry gas pressure gauge may
also be used for either test.
5.1.1 Checking the Main Line
Gas Pressure
1. Attach a manometer (or a dry gas pressure gauge)
to heater jacket (see Figure 36).
2. Open both columns on the manometer.
3. Use shutoff valve outside the heater jacket to shut
off all gas supply to the heater.
4. Remove the 1/8 inch (3.2 mm) NPT test plug in
the inlet side of the gas valve and replace it with
the 1/8 inch (3.2 mm) NPT fitting from the
manometer kit.
1. Open the drain valve on the left side of the
heater.
2. Remove the large, hex-head plug located on the
right side of the heater under the in/out header
(see Figure 34). Perform this inspection after 60
days of and after 120 days of operation. This will
establish a regular inspection routine.
4.2.2 Cleaning the Heat Exchanger
An inspection and cleaning of the complete heat
exchanger can only be done by removing it from the
heater.
1. Remove the heat exchanger.
WARNING
Black carbon soot buildup on a dirty heat exchanger
can be ignited by a random spark or flame. To
prevent this happening, dampen the soot deposits
with a wet brush or fine water spray before
servicing the heat exchanger.
2. Remove the heat baffles and check for a light
accumulation of soot or corrosion on the outside
of the heat exchanger tubes.
NOTE: While the heat exchanger is out of the heater,
inspect the firewall refractory insulation blocks for
cracks, wear, and breakage. Replace if necessary.
3. Use a wire brush to remove soot and loose scale
from the heat exchanger. Do not use water or
compressed air for cleaning.
NOTE: Use only the correct carbide tipped reamers
which are available from Laars.
4. Ream the insides of the tubes (see Figure 35).
5. Pull the reamer out frequently to remove lime
powder and prevent the drill from binding in the
tube.
6. Install new gaskets. Do not reuse the old ones.
Figure 35. Heat Exchanger Tube Cleaning.
Notes:
1.
When pressure relief valve is used, it must be removed and the hole plugged, as shown.
2. Remove the plug before reinstalling the heat exchanger.
City
Water
Supply
400-500 RPM
Drill Motor
OUT OF
PRODUCTION