Reliant FVIR GAS WATER HEATER Technical Information PDF herunterladen (Seite 67)

RESIDENTIAL GAS AND ELECTRIC WATER HEATER

TROUBLESHOOTING and SERVICE HANDBOOK

RELIANCE Water Heater Company Technical Training Department

THERMAL EXPANSION

SYMPTOMS

Effects are only noticeable after hot water use followed by periods of no water use.

Relief valve drips during any recovery cycle when no hot or cold water is used.

Hot water pipes creak while heater is recovering and all valves are closed.

Tanks or other components of the water supply system fail prematurely.

A metallic creaking noise might actually be heard in the location of the heater as the

pressure is relieved and the stretched tank returns to a natural shape.

Faucets drips during any recovery cycle when no hot or cold water is used.

Water surges when a valve is first open and then pressure drops.

CAUSE

The water in a water heating system expands when it is heated and has a greater

volume. Since water will not compress (like air), system designers must include

provisions for thermal expansion. (Water in a closed tank at 50 psi, when heated just

10 degrees, will reach a pressure of 250 psi).

Many water supply systems have check valves at the water meter to prevent any

possible contamination of the public water supply by the accidental back-flow of

contaminated water into the supply mains. These check valves are often required by

code, and some cities are even installing the check valves. They serve a useful

purpose. Do not remove them!

The use of pressure reducing valves (PRV) is another cause. PRVs are designed to

conserve water and prolong fixture life. Many PRVs also act as very effective check

valves. Again, do not remove them!

Water softeners in the system may also act as back-flow preventers.

TEST

Follow these easy steps to diagnose thermal expansion:

Turn the heater thermostat all the way down, and install a water pressure gauge with dead

hand (AOS part #4798) on the drain valve. Open the drain valve, so the gauge reads system

pressure.

Open a hot water tap and allow 15% to 20% of the tanks volume to run out. Shut off the

drain valve and make sure that no other fixture in the system, hot or cold, is open. Make sure

that outside fixtures, if they are on the same system, are turned off too. Any water leaks or

use will make the test meaningless.

Check the water pressure gauge, and turn the pointer so it lines up with the pressure

indicating needle. Turn the thermostat back up to its normal position, so the heater cycles

on. Watch the pressure gauge.

If the system is closed, the pressure will start to climb steadily and rapidly. A small amount of

thermal expansion control may be built into the system because of trapped air pockets or a

water hammer arrestor. In that case the pressure will increase slightly, hold steady for a

short time and then rapidly increase. The temperature and pressure relief valve (T&P) or

PRV should open and release water once the pressure reaches the maximum setting on the

valve. The valve will close once the pressure falls below the pressure setting of the valve.

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