Reliant FVIR GAS WATER HEATER Technical Information PDF herunterladen (Seite 71)

RESIDENTIAL GAS AND ELECTRIC WATER HEATER

TROUBLESHOOTING and SERVICE HANDBOOK

RELIANCE Water Heater Company Technical Training Department

"Capping" takes place when a downward force equal to or

greater than the pilot draft is present in the vent. Because

of a poorly designed vent, wind outside the structure, will

push down the vent and cause the flue to stall. This is

most evident in high wind situations but can happen in

much calmer atmospheric conditions, or in combination

with one of the other two pilot outage reasons. When the

flue stalls, the draft from the pilot flame stops rising up the

flue, all the oxygen is used up and the pilot flame goes out.

It takes less than 1/500th of an inch water column

pressure to stall the flue. This can be caused by an

improperly designed or installed vent termination, a vent

termination that does not extend two feet above anything

within a ten foot radius horizontally on the roof, a vent with

no termination on it, or a vent that is too big for the heater.

(See figure to right).

The second reason that contributes to pilot outage is high

ambient temperatures. This effects heaters that are installed in

attics, garages, unconditioned spaces or heaters that draw

makeup air from an attic spaces. Soaring temps in the attic can

peak at 160°F or higher in the summer months. If the tank

temperature is set at 135° F, and the air in the attic is a

sweltering 160° F, the heat generated by the pilot is not enough

to heat the surrounding air adequately enough to start a draft

(upward air movement) and the pilot will burn up all the

available oxygen and extinguish. Atmospheric water heaters

depend on heated flue gas to carry the products of combustion

up and out due to the buoyancy of the flue gasses. Ventilation

of the attic becomes a big issue. The hotter the air is the more

it wants to rise. If the heater is getting combustion air from the

attic, the hot air in the attic does not come down the makeup air

vents to feed the burner and the pilot goes out from lack of

oxygen. (See figure 2)

Decompression is the third reason that the pilot flame will fail.

Decompression happens when the air pressure inside the

structure where the water heater is located, drops below the outside air pressure. If air can not enter the

structure as fast as it is being used then the building will go “negative.” If the room pressure is negative,

then the air pressure outside will push down the vent to equalize the pressure. The effect is much like

“capping”, the combustion products from the pilot stall in the heater flue pipe, and the pilot runs out of

oxygen because there is no draft (upward air movement) to replace the oxygen. Reasons for a room or

building to go negative are a closed room (no make up air vents) without much, or no foot traffic, a room

that is too small to support the needs of the heater, an attic or kitchen fan that exhaust air out of the

structure without bringing in its own makeup air, or combustion air shared by two or more gas burning

appliances.

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Reliant FVIR GAS WATER HEATER Technical Information Seite 71

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