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Closed system
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What
is Thermal
Expansion Closed system |
 Electric water heater thermostats Thermostats stick melt and come out of calibration... replace thermostat Symptoms: Cold water, uneven temperatures, reset tripping, TP releasing water Buy: Water heater thermostats at Amazon Resources: How to replace electric water heater thermostat Add another thermostat to water heater How to wire thermostats Marathon water heater thermostats Two water heaters Troubleshoot electric water heater |
  Gas water heater thermostats If tank is overheating or not heating correctly, replace thermostat Symptoms: Cold water, uneven temperatures, TP releasing water Buy: Gas water heater thermostats at Amazon Resources: How to replace gas water heater thermostat Add another thermostat to water heater Troubleshoot gas water heater |
 Closed system is caused by thermal expansionWater heater causes expansion of water .... Heating water causes volume of water to expand, water does not compress, so pressure builds up. The pressure normally pushes back out onto the cold water line. Check valves and incoming pressure reducing valves can create a closed system where dangerous pressure builds up inside the water lines due to the water heater... A recirculation system and other plumbing installations sometimes cause the need for check valve. The check valve stops the water from expanding back out into the cold water line. Solution: install pressure reducing tank, or expansion tank anywhere on cold water line between tank and check valve ... the result: pressure from heated water expands into the expansion tank. Buy: Expansion tanks at Amazon  Resource: Expansion Tank Installation pdf Closed system / pdf | |
| Thermal expansion 'The water in a water heating system expands when it is heated and has a greater volume. Since water does not compress like air, the expansion causes high pressure inside the water heater and plumbing system. Thermal expansion, and the resulting high water pressure are a major consideration when designing water heaters and plumbing systems. For example, residential water heating tanks are rated at 300 psi (when new), with 150 psi maximum safe operation. The TP valve releases water pressure when pressure exceeds 150 psi .... but 150 psi poses a serious risk to older tanks that are rusted, and for plumbing pipes and fixtures in general. High pressure causes plumbing failures and early demise of heater. Maximum incoming water pressure is 80 psi, with 50 psi recommended. If pressure is above recommended, then a pressure reducing valve is installed, along with an expansion tank. The pressure-reducing valve and correctly-sized expansion tank are installed on incoming cold water line Normal water heater operation will push the pressure back through the incoming cold water line, and out to the water main, or push pressure back into the water well tank. Water expands approximately .00023% per degree F temperature rise. In a normal system (not closed): ''Water expands approximately 2% in volume for a 100°F temperature rise (from 40°F to 140°F) ....40 gallon water heater, water being heated to its thermostat setting will end up expanding to about 40.53 gallons.'' This amount of thermal expansion, equal to about 1/2 gallon of water, can be easily absorbed back into the incoming cold water line. In a closed system, the water expansion dynamic is much different. If the incoming cold water line has a check valve at water meter, a pressure reducing valve (PRV), or sometimes a water softener can cause the problem, the pressure from thermal expansion will get backed up. The expanding water cannot be pushed out into the water main, and the pressure builds up because water doesn't compress. For example, in a closed system where water is confined to a storage tank, a temperature rise of just 10°F (increasing from 75° to 85°F), increases pressure from 50 psi to 250 psi. This amount of pressure will quickly exceed the TP rating, causing water to be released in a series of short bursts, except when water is being used.' Troubleshoot TP valve Symptoms of thermal expansion • ''Expulsion of water from TP. 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.'' ''Periodic discharge of the temperature and pressure relief valve may be due to thermal expansion in a closed water supply system. The water utility supply meter may contain a check valve, backflow preventer or water pressure reducing valve. This will create a closed water system. During the heating cycle of the water heater, the water expands causing pressure inside the water heater to increase. The temperature and pressure relief valve may discharge hot water under these conditions which results in a loss of energy and a build-up of lime on the relief valve seat. To prevent this from happening, there are two recommendations: 1. Install a 125 PSI pressure relief valve in the cold water supply line. Make sure the discharge of this valve is directed to an open drain and protected from freezing. 2. Install a diaphragm-type expansion tank that is suitable for potable water on the cold water supply line. The expansion tank must have a minimum capacity of 1.5 U.S. gallons for every 50 gallons of stored water.'' |
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 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.'' Buy: Water pressure gauges Watts telltale Pressure Gauge 276H300 Temperature pressure gauge Telltale pressure gauge is left in place for a day, and marks the highest pressure so user can tell if there are pressure spikes that are causing TP valve to leak water, or other possible problems Resource Troubleshoot and identify water heater valves |
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 TP
valve / temperature-pressure
valveMechanical 2 in 1 protection against excessive pressure and excessive temperature. TP valve will release water when conditions exceed TP valve rating, causing cold water to enter tank. This reduces both pressure and temperature. TP valve automatically closes when emergency conditions are over. Lift and gently lower TP valve once each year. Residential water heaters are pressure tested to 300 pounds per square inch (PSI) and have a working pressure of 150 PSI. T&P valve will open when the pressure inside the tank exceeds 150 PSI, allowing pressure to vent safely. T&P valve will open if water temperature at top of tank reaches 210°F depending on water heater, and TP valve rating. Commercial heaters can be rated for higher temperatures and pressures than typical residential heaters. TP valve must be rated for more BTU than tank rating so that release of temperature and pressure can outpace ability of tank to heat water.  Buy: TP
valves:Replacement TP valves at Amazon Teflon tape at Amazon Resource: How to troubleshoot and replace TP valve TP valve code |
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| Reduce
pressure with
expansion tank
Pressure
over 80 psi can damage water heater and pipes over time. 150 PSI maximum allowable working pressure on residential water heater, but water pressure increases when heated. Install expansion tank anywhere on cold water line, between any check valve or pressure reducing valve and water heater Hot water will expand back into water line and then into expansion tank, preventing long-term damaging to pipes and fixtures and water heater Closed system: Water confined to a storage tank or piping system, when subjected to a temperature rise of 10°F (increasing from 75° to 85°), increases pressure from 50 psi to 250 psi. Normal system without check valves etc: Water expands approximately 2% in volume for a 100°F temperature rise (from 40°F to 140°F) ....40 gallon water heater, water being heated to its thermostat setting will end up expanding to about 40.53 gallons. Buy: Expansion tanks at Amazon Resource: Expansion Tank Installation pdf Closed system / pdf |
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Pressure
reducing valve High pressure over 80psi can damage water heater and plumbing Install expansion tank, and/or pressure reducing valve Pressure reducing valve is installed on cold water supply line to regulate and stabilize flow pressure FYI: for a closed system: Water confined to a storage tank or piping system, when subjected to a temperature rise of 10°F (increasing from 75° to 85°), increases pressure from 50 psi to 250 psi ... Normal system without check valves etc: Water expands approximately 2% in volume for a 100°F temperature rise (from 40°F to 140°F) Buy: Pressure reducing valves Pressure regulating valves at Amazon Resource: Watts pressure reducing valves/ pdf |
| Higher pressures change the boiling
temperature. Water boils at 212°F –
at sea level – unless the water is contained under
pressure. At 52 psi gauge pressure, water would not boil until it
exceeded 300° F. The TP valve would release hot water and cold water
would enter tank to prevent steam explosion and tank rupture. Never cap
off the TP valve if it is leaking. Typical bath shower is 105°F. Setting thermostat to 120°F helps prevent thermal expansion, and shortened life or tank and plumbing from high pressure. More chemicals are percolated out of water at high temperatures. Water stored at 140°F in the tank may accumulate 19 lbs. of lime per year. 160°F in the tank may accumulate 85 lbs. of lime per year. 180°F in the tank may accumulate 135 lbs. of lime per year. More gasses are separated as water temperatures rise. Air in water line |
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