BDP Furnace Ignites Pilot not Main Burner?

[Tomlich1]

I have a BDP Model 518A048CC model 75,000 btu furnace, looks like made in 1978. The pilot ignites and stays ignited, yet the main burner doesn't kick on. Is it the gas valve, could it be the igniter?

Any help would be appreciated

Thanks!

[HayZee518]

sounds like it's the main burner valve because the pilot valve stays on [open] meaning the pilot flame is being detected by the thermocouple and so, is generating the small 750 millivolt signal to keep the pilot valve open. there's a very small electro magnet inside the valve connected to the pilot orifice. on the backside of the pilot orifice is a spring that makes the pilot orifice snap shut when the milli volt signal is not there. on most gas hot water tanks, you know, when you go to light the pilot, they say turn the knob to pilot - press and hold the button in for three minutes and light the pilot flame. what they mean is when you press the button in, you are opening the pilot orifice manually and pushing the guts towards the electro magnet. once the millivolt generator produces the dc for the magnet, when you release the button, the magnet keeps the pilot valve open. then they say to turn the knob to ON or OPERATE. then the tank thermostat takes over and opens the main valve to heat the water until the aquastat is satisfied, which shuts down the main burner valve. Same idea in a furnace only instead of an aquastat, the room thermostat operates the main burner.

[Tomlich1]

I don't see a thermocouple on the pilot, it has the igniter rod that draws the spark, does that serve boh purposes?

Could it be the wall thermostat also?

When you turn the fan on to maual "on" on the thermostat the fan turns on.

[HayZee518]

ok, yah, the spark rod also serves as the flamerod to detect a flame. check with a voltmeter if you have 24 volts going into the stat and 24 volts coming out of it. check at the gas valve to see if you have 24 volts here. if the voltage is there but nothing happens then replace the valve. be prepared to spend about 200 dollars for the valve.

[paul52446m]

I have a BDP Model 518A048CC model 75,000 btu furnace, looks like made in 1978. The pilot ignites and stays ignited, yet the main burner doesn't kick on. Is it the gas valve, could it be the igniter?

Any help would be appreciated

Thanks!

Take some sand paper and clean the flame rod and then see if it fires up.
later paul

[Tomlich1]

All is took was a little sand paper and I moved the flame rod up further into the pilot flame path and it fired up no problem.

Thanks to all for assistance. A HVac repairman said it neede a new igniter and quoted $500 for the part alone. Caveat emptor, A lot of crooks out there.

thanks again!