Gas Valves
On gas-fired heating systems, the main furnace gas valve is one of the most important components. It contains most of the brains of the heating system. Its operation is simple. It is designed to open and allow gas into the combustion chamber; however, it uses feedback from several safety devices to determine whether it is safe or appropriate to allow gas into the combustion chamber. The reliability of gas valves is high. Replacement is neither difficult nor terribly expensive.
A particular White-Rodgers gas valve has been known to cause overheating problems as a result of an intermittent malfunction. The valve in question is a White-Rodgers 36B series. Valves which are date coded 7630 through to 7752 are the ones which are considered to be problematic. If any Model 36-B gas valve is present, a heating contractor, the furnace manufacturer, or the valve manufacturer should be contacted.
Gas Burners
The most common gas burners are point source burners, ring burners and ribbon burners. Furnace burners get dirty and the small orifices (particularly on ribbon burners) plug with debris. Burners also become misaligned and the flame does not point in the right direction. Burners can also rust.
The air supply can be restricted if the furnace burners are in a small closed room or if the burners are dirty or incorrectly adjusted. This results in incomplete combustion, higher heating costs, and, in some cases, condensation problems. In severe cases, carbon monoxide poisoning may occur. This is a life threatening situation.
On some heating systems (particularly with ribbon burners) "flashback" is a common phenomenon when the system first starts up. While this is not a problem with the furnace burners themselves, the resultant damage is caused by the burners. In a flash-back situation, some of the ignited gas spills out of the front of the heating system. Heat shields, provided on most systems, prevent any serious damage under these conditions; however, in extreme cases, control wiring and other components of the heating system have been badly burned. If there is any evidence of scorching or burning outside the combustion chamber, a specialist should be contacted.
Oil Burners
Oil furnace burners consist of a fan to force air into the combustion chamber, a pump to force oil into the combustion chamber, a nozzle to convert the oil to a fine mist, and an ignition system to ignite it. During a visual examination of a heating system, very little of the oil burner can be inspected, due to its design. Problems can occur with any of these components and a specialist should be contacted.
Even burners which are working may be burning very inefficiently, and heating costs will rise. Oil burners should be serviced annually. Old systems should have an annual efficiency test. Efficiency cannot be tested during a home inspection. Furnace burners starved for air will be costly to operate and may generate dangerous carbon monoxide gas.
Refractories
A refractory is found in some boilers and furnaces. It may be a similar material to firebrick found in fireplaces and, in some cases, is firebrick. Its purpose is to protect the other components from direct contact with the flame. Refractory deteriorates with time and exposure to flame and requires repair or replacement from time to time. It is often not visible without dismantling the system or breaking a mortar seal.
Pilotless Ignition
Oil-fired systems and some mid and high efficiency gas systems do not have a pilot. On these systems, a spark or hot surface ignition system (a spinning "grinding wheel" which glows white hot) is used to ignite the fuel when heat is called for. These systems contain a safety device which shuts down the entire heating system if ignition is not proved after a certain amount of time. Depending upon the arrangement of the system, some will try again after a certain period, while others will not. This can pose a problem in an unattended house as the heat can be off for long periods of time until the problem is discovered.
Oil Tanks
Oil tanks should be 10 feet from burners. Oil tanks are usually maintenance free; however, leaks can occur in the tank, filter and oil line leading to the burner. Leaking filters and lines can be easily repaired or replaced; however, repairing a leaking tank is seldom done. Most are replaced. Some tanks are located outdoors underground. Inspection of these is not possible during a home inspection.
Leakage from tanks is usually the result of rusting which occurs due to water in the tank (from condensation). It settles to the bottom of the tank as it is heavier than oil. This is where most of the rusting occurs. It is best to keep the tank full during the summer months to keep condensation to a minimum.
2007 Sears Brands, LLC. All rights reserved.