Hydro flame furnace Model 7225

RV Type: Motorhome
Model: Vanguard
Year: 1978
Description of Problem: Hydro flame furnace Model 7225 was running fine. Went on vacation and lit pilot when burner started it started to warm then burner backfires. It cut the burner to half of the tubes and makes whistles around the orfice intakes.the gas valve is running 11″ WC . All burners are clean.

Our Answer

Hi: This sounds a bit strange but there could be something blocking the air intake to the main burner. If this is starved for fresh air the flames are reduced or maybe even extinguished.  The backfire could be caused by an air leak from the burning chamber and the explosion may have caused something to dislodge.  On most of these furnaces your air intake is part of the exhaust vent, and even if un-burnt gases from the exhaust are recycled into the burning chamber you will have combustion problems. The whistle indicate the air is trying to get to the burner in sufficient volume but is unable to do so.

Sorry I can’t be of more help, I am just going from experience and probabilities.


Follow up:

Thankyou, although there seems to be no restriction and the burners have been cleaned. The manifold pressure is 11″ wc as required on the spec sheet. This backfire does not occur when unit first fires until it warms the furnace then it backfires every time it calls for heat. The burners still burn flame but fire backs in the burner tube about 2″ from the orfice’s there are 3 on this unit.

Our Answer:

Hi again: I am trying to visualize this, does the flame go inside the burner tube or is it that the flame goes only 2 “ down the tube.You have three burner tubes, but only one orifice right, the burner tubes are connected by a manifold. (I do not have my drawings available so I am working from memory, you wouldn’t believe how many furnaces there are out there).

The air for the burners should come in around the orifice to provide a gas air mixture to burn. The air pressure from the fan should force the air down the burner tubes to provide the flame intensity at the burner ports. If this is reduced the flame would burn orange, and if too intense it would levitate from, the burners. Has the orifice in the burner been cleaned and possibly enlarged? These are critical for size and should never have anything other than air pressure or a liquid like alcohol blown through them.

Sometimes people use a fine wire to clean the orifice and this is a definite no-no. It doesn’t take much to enlarge the orifice and then you can have similar problems. Some of these orifices have a ruby embedded to limit gas flow, but this is usually in fridges, and if wires are pushed through they are useless. Backfires are usually caused by excess gas and not enough air until the ratio reaches the right point for combustion and the ignition is forceful and causes the explosion you hear as a backfire.

I hope this helps, please let me know if you find additional problems, or if you resolve the issue.


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