LAARS Mighty Therm LO-NOx PW (Sizes 500-1825) - Install and Operating Manual - Manual (Page 11)

Mighty Therm Lo-NOx Page 11
on the inner walls of the tube which reduces the inner
diameter of the tube. Scale can be any color or
texture; smooth or rough, granular or amorphous.
Signs of erosion are generally pitting, cavitation,
ridges and “islands” on the inner walls of the tubes.
Since this condition results from extremely soft water
sources, or as a result of a water softening program,
the internal copper surfaces will be extremely shiny.
Other chemicals, such as chlorine or chlorides in the
water, will cause dark surfaces of erosion.
In areas where the water supply is extremely
corrosive, it is advisable to order the heater with
cupro-nickel tubes in the exchanger.
Damage From Scaling, Corrosion, or Erosion
is Not Covered by the Warranty.
3.3.2 Piping System Requirements
1. Check piping diagrams with local applicable
plumbing, heating and building safety codes.
2. All two-temperature systems using temperature
valves must have forced recirculation in the low
temperature building loop.
3. A check valve installed at the hot water inlet to
the tempering valve will prevent cold water from
being drawn in reverse through the tempering
valve into the hot water.
4. When installing a tempering valve, place at
bottom of antithermosyphon loop at least 24"
high to prevent excessive hot water from
entering mixed water supply. Bring the cold
water supply up from the floor to the valve (see
Figure 10).
The following suggestions may solve the
problem:
1. Replace the installed water pressure reducing
valve with a suitable valve having a back flow
port. These valves have a back flow port which
allows water to flow backwards when the
pressure in the system exceeds the pressure in
the mains.
2. Install a check valve around the pressure
reducing valve to permit reverse flow. This will
allow the expanded water to back flow into the
mains (see Figure 11).
Figure 10. Tempering Valve Installation.
3.3.3 Water Expansion
When cold water is heated the water expands. If
no water is being used during the heat-up period the
expanded water will normally back up into the city
mains.
A water pressure reducing valve installed in the
incoming cold water line may act as a check valve and
prevent the expanded water from moving backward.
This will cause pressure to rise in the heater, which
will be relieved by the pressure relief valve.
If the relief valve pops frequently a mineral
deposit may build up on the valve seat, causing it to
leak.
Figure 11. Check Valve/Pressure Reducing Valve
Installation.
3. Install an auxiliary small relief valve set at 25 psi
less than the main relief valve. The valve must
be piped to a drain and may require occasional
cleaning. It will bleed off the expanded water
and protect the main pressure relief valve from
becoming fouled.
4. Install a properly sized expansion tank.
3.3.4 Pump Requirements
1. The factory provided pump on PW heaters are
sized to provide proper circulation through the
heater and heater-to-tank circulation loop (see
Figures 12, 13 and 14). If the heater-to-tank
circulation loop does not contain more than 6
elbows and 30 feet of pipe, use pipe fittings in
the loop no smaller than the following:
Model Pipe Size
500 through 715 2"
999 through 1825 2-1/2"
If the heater-to-tank circulating loop contains
more than 6 elbows and 30 feet of pipe, use
pipe or fittings in the loop no smaller than the
following:
Model Pipe Size
500 through 715 2-1/2"
999 through 1825 3"