Why does my gas wall furnace have a big flash of fire and then whoosh?
I just replaced our gas valve (white/rogers universal combination gas valve 36c03) and the thermpile/pilot burner. Since the replacement of new parts when the burners are being lit there's a big whoosh sound and then a huge like fire flash and the house rattles. I'm very converned, I know it has to do with the build-up of gas before the actual burners igniting, but I don't want to start fooling with the adjustment screws and such until I get an experts opinion. The pilot flame I believe is up too high because compared to what it looked like before, the flame is alot larger and is sputtering and the pilot is much more engolfed. Where as before it was a small blue flame just surrounding the thermopile tip. Please help asap as I'm worried it might be a dangerous situation and it's a ticking time bomb.
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I did not see that your indoor fan motor started. Near your indoor fan motor there is a temperature switch that is called the fan delay relay. On a temperature rise the relay shuts a contact that turns on the indoor fan motor. If the contact does not close the high temperature limit will shut the gas controls off like your getting. A fan delay relay also allows the fan to run a minute or so to carry away the remaining heat in the furnace and help cool the furnace down. The fan delay relay is normally mounted in a recessed area in the fire wall of the furnace plate. I have also seen them on the top of the furnace heat exchanger. Anyway, the fan delay relay will probably not be available on a sunday, so temporarily until parts are available, try turning the thermostat fan from auto to on and try the furnace again. By turning on the fan to on the high temp limit will not shut you down again.
I have had high temp limit change there trip points, but you said you bypassed it and did the same thing.
Another cause could be using the wrong type of air filter. The new pleated filters sold block to much air flow. If air mass flow rate drops the difference in temperatur go up and when the difference in temperature go up, it gets nearer the high limit and causes it to trip. All pleated filters drop normal air flow through ducts by at least 35%. To make your air duct system work properly use the what is called throw away filters which cost about 1/3 the cost of the pleated filter. Remember to either clean or change the throw away filter monthly to reduce dirt being drawn into your duct system.
Hope this helps.
Make sure the gas valve is turned to the ON position after you had it in PILOT position. Also check the thermostat low voltage wiring @ furnace...jumper the Red & White wires to bypass the thermostat temporarily. Make sure there is 24 volts on you low voltage circuit.
Before replacing the gas valve, make sure that the limit switch is not tripped. I have seen techs wire the limit in so that the pilot will also shut off. The limit is usually at the top of the heater or mid way down, behind the casing. As for replacing the gas valve, you can replace it with a universal combination gas valve, they have multiple brands that can match pretty close to your valve. They can run over $100.00 easily and here, you have to have a contractors license to buy one. Hope this helps! Happy Holidays!
Trane unit ,same White -Rogers gas valve. I have replaced both the gas valve and the thermocouple . Have agreat robust blue pilot while the button is pushed in , let go and the flame does not stay lit . I checked the milly D C volts and have better than 20 . Is there a problem with the new gas valve or the couple not generating enough volts or is there a safty I do not know about that could be open ?
Assuming this is a wall furnace, take a AA battery and attach one wire to each end, tape or use holder from toy at 99 cent store!!
look at the pilot assembly, 2 wires(may look like one) go to the gas valve. at the gas valve it will be 2 wires attached to the gas valve.
this powers the whole thing! simply atach the 2 wires from batt, to where the pilotwires go (not the thermostat wires, the pilot generator)
tryt now ! does it work? if not , bad valve or try connecting the two stat wies together at the furnace instead of stat doing it to test if stats bad or wires bad. dot keep using it with battery if your sleeping or leaving etc, as ,if the pilot blows out, the gas can flow as if a plt flame existed!!!
flooding gas out into a flameless environment.