"Gunner" wrote in message
...
Existing installation, just getting flakier and flakier. I dont have
any way to test the manifold pressure (gas), or the blower pressure,
though the blower does have a shunt to increase or decrease blower
pressure. Its never been moved as far as I can see.

Ok. You could take some clear plastic tubing and build a manometer. Or
if push came to shove, put in a Schrader valve and use a tire gauge to get a
rough reading. But the gas pressure probably isn't the problem since it is
a preexisting system, unless the pressure regulator for the gas has gone
bad.
Another things to consider, since we can't see the setup, is the
environment. Is it in a humid or dusty area? Humidity can cause spade
connections to corrode, and if it is bad it can cause the burner to rust
inside and the rust can block the gas flow.. Dust can get into burners and
block the gas flow. It is a heater system to remove water from oil. Is the
water vented outside or inside where the unit is? Is there any corrosive
chemical used in the area? If so, connections may be corroding. Take a
good look at the inside of the unit to see if it looks like water has been
condensing in it. If so, the controller may have simply gone bad due to the
water.
Others have mentioned the flame sensor may be dirty. That could easily
be the case especially if the flames have any yellow in them, the flames
should burn blue. Yellow means incomplete combustion and sooting. Check
the inside of the combustion chamber for sooting. Remove the flame sensor
and wipe the sensor with a clean paper towel.. A little discoloration on the
towel is normal but there shouldn't be black soot or at least very little.
If cleaning the sensor solves the problem, inspect the inside of the burner
to insure it is not blocked with foreign matter(dust, insect, rust,etc.),
adjust the air inlet(s) on the burner(s) to eliminate any yellow flame. If
the blower supplies the air for the burner, adjust the blower to eliminate
any yellow flame.
If the system is a very old one consider the gas line for a moment. Does
it have a drip leg. If it has a drip leg at the unit, you might turn off the
gas and remove the drip leg to insure that it isn't full. If for some
reason oil or water has filled the drip leg it could be causing the flame to
burn yellow and soot. But honestly, I've never seen a drip leg get that
full. If it doesn't have a drip leg you might install one to prevent any
oil or moisture from making it to the gas valve and burner. I take it the
lines are iron pipe since you said they were 1". But since the unit has
been there for some time any oil in the pipes that could migrate to the unit
has probably already done so.

Loyd