LAARS Mighty Therm VW-PW (Sizes 175-400) - Installation, Operation and Maintenance Instructions - Manual (Page 24)

LAARS Heating Systems
Page 24
4.3 HEAT EXCHANGER
4.3.1 Inspecting the Heat Exchanger
To check the scale buildup, periodically inspect
the tube having the highest temperature as follows:
1. Open the drain valve on the left side of the
heater.
2. Remove the hex-head plug located on the right
side of the heater under the in/out header (see
Figure 32). Perform this inspection after 60 days
of and after 120 days of operation. This will
establish a regular inspection routine.
4.3.2 Cleaning the Heat Exchanger
An inspection and cleaning of the complete heat
exchanger can only be done by removing it from the
heater.
1. To remove the heat exchanger, refer to Section
2.6.1.
Caution
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 33).
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.
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 (see
Figure 33).
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. To reinstall the heat exchanger, refer to Section
2.6.1.
SECTION 5.
Troubleshooting and Service
5.1 Gas Pressure Tests
Use the following procedures to check the main
gas and manifold regulated 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 34).
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 Allen Plug on the inlet side
of the gas valve and replace it with the 1/8 inch
(3.2 mm) NPT fitting from the manometer kit.
Figure 34. Gas pressure test.