Transcript
TWH-V-28 page 1 of 2 rev 01/06
CORRODED BLOCK MODELS:
WARNIN G ARNING
80VP, 125VP, 170VP
LP & N G ARE EXTREMEL NG EXTREMELY FLAMMABLE Y FL AMMABLE SO UTIONS WHEN PRECAUTIONS TAKE EXTRA PRECA PERF ORMIN G ANY W ORK T O THE HEA TER PERFORMIN WORK TO HEATER
A corroded block is fairly rare. During our investigation of similar occurrences, we discovered the following as the usual causes: 1. Damaging water conditions 2. Improper draft 3. Freezing
Damaging water conditions Damaging water conditions include sand, dirt or debris in the water supply. Hard water and/or overly hot inlet water can also cause this problem. These conditions can damage the seals between the water valve assembly and the gas valve assembly. In some cases the pushrod assembly becomes abraded or coated with mineral scale. In other cases, the seals around the pushrod get cut or become non-resilient. Either way, water begins to leak into the gas valve assembly. If unchecked, corrosion will begin and can spread until the entire control assembly becomes unsalvageable.
Improper draft • Improper draft is often the hidden culprit in these
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occurrences. Proper draft is a combination of things. It involves having the proper chimney and/or flue pipe. Proper draft also requires an abundant supply of inlet air at neutral pressure. Proper draft is not as simple as it sounds. Very often, other appliances suck air from the inside and forces air to the outside of buildings. These appliances include ventilation/exhaust fans, fireplaces, wood burning stoves, furnaces and clothes dryers. If air pressure inside the building is lower than air pressure outside the building, backdrafting occurs.
©BBT NORTH AMERICA Bosch Group
• With improper drafting, hot combustion gases are not
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evacuated from the heater as they should be. The backed up heat can cause minerals in the water to precipitate within the water valve assembly (heated water accelerates scale deposits). The result is similar to that at tained with "damaging water conditions," above. More serious than damage to the heater is the health threat backdrafting poses. Without an adequate fresh air supply, a continuously operating heater could deplete the oxygen supply in a building. Furthermore, if combustion gases are not exhausted properly, they may spill back into the building. The most dangerous of these, carbon monoxide, can cause serious illness or even death. If backdrafting occurs while the heater is not operating, parts of the heater may freeze during the winter months. Nothing else in the house may freeze. It may not even be all that cold outside. The constant downward flow of cool air can freeze the water in the water valve assembly.
Freezing Freezing may occur when a heater is installed in an insufficiently heated space, or when it is improperly drafted (see above). Usually, the first place that water freezes is in the water valve assembly. As it expands, it exerts pressure on the diaphragm and ruptures it, the rubber seals on the pushrod begin to weaken, which may allow water to pass by them into the gas valve.
Bosch Water Heating 340 Mad River Park, Waitsfield, VT 05673
TWH-V-28 page 2 of 2 rev 01/06
CORRODED BLOCK Regular inspection Regardless of the cause, extensive corrosion takes time. Regular inspection of the heater can detect these and other potential problems before they get out of hand. If you wait until your heater no longer operates correctly before you inspect, you may be too late. 1. Check the area around the heater. Be certain that no flammable materials have been placed below or on top of the heater. Make certain that there is adequate clearance below and in front of the heater to ensure good air flow to the heater (see Clearances Chart with heater). 2. Check draft: a. Close all doors and windows to the outside. b. Turn on all appliances that force air out of the building. These include all exhaust/ventilation fans, furnaces, clothes dryers, wood burning stoves, etc. c. Open all doors between the AquaStar and these other appliances. d. With the heater not running, hold a smoke source (cigaret te, incense, candle, etc.) near the louvres at the front of the heater. The smoke should get sucked into the louvres. If the smoke comes back towards you, there is a backdraft. It can freeze up. e. Then, turn on a hot water faucet so that the burners are operating. Do another smoke test (similar to "d"). If smoke comes back towards you while the heater operates, carbon monoxide is spilling back into the building. This is a serious health hazard and must be corrected. 3. Check the operation of the pressure relief valve. Be certain that the discharge from the valve will go where it will do no damage.
©BBT NORTH AMERICA Bosch Group
4. Check thermostat operation. Turn the temperature selection knob to the number 2 position. Turn on a hot water faucet to about 1½ gallons per minute (will fill a quart container every 10 seconds). Check the temperature of the outlet water; if hotter than 115°, your thermostat is either out of calibration or inoperative. 5. Check the flow rate at which the burners come on. They should come on at between .75 and 1.00 gpm. If a faster flow rate is required to turn on the burners, there is a problem in the water valve assembly, or you may have cold water crossing over into your hot water line after the AquaStar. 6. Check to see that the burners shut off immediately when the water flow stops. If not, there is a problem in the water valve assembly. 7. Push in and turn the pilot lighting button to the single flame set ting to prevent the burners from coming on while you do the following check: • Remove the front cover of the heater. Inspect the heat exchanger for soot and signs of water leakage. Note that soot is a sign of improper combustion; check for the cause. Vacuum or brush any debris or soot from the heat exchanger fins. Anything blocking free air flow through the fins will eventually cause the heat exchanger to burn out. 8. Inspect where the water valve assembly meets the gas valve assembly. If there is any moisture, signs of leaking water or whitish or greenish powder, t he pushrod seal is leaking and needs to be replaced. 9. Inspect the pilot assembly. See that the flame is reaching the thermocouple. If the flame is yellow, make certain that the pilot air filter is clean. If the flame is too small, follow the instructions in the installation manual for cleaning the pilot assembly.
Bosch Water Heating 340 Mad River Park, Waitsfield, VT 05673
