C. Fuel Line Leak Guide
Fuel line leaks can develop over time,
especially in unprotected fuel lines that are buried
in concrete. Sudden leaks can also occur as
the result of activities that have nothing to do
with the heating system, such as the building
settling or contractors working on the property
accidentally damaging the line. Workers who
were landscaping, gardening, exterminating,
installing underground sprinkler systems or
performing other activities may have damaged
fuel lines without knowing it.
Leaking suction lines do not always cause
the burner to stop operating because they are
sometimes operating on gravity or siphon
flow and leaks go undetected. However, slight
suction line leaks can lead to service problems
including: rough starts, rough stops, noise, after
drip, etc.
Unfortunately, leaking return lines cause no
such problems – but they can cause serious
environmental damage. Since leaking return
lines do not affect burner performance they can
go undetected for a long period of time before
being discovered. While suction lines can be
checked for leaks by following the procedure
outlined below, return lines can’t always be
checked with confidence because they often
terminate above the fuel level in the tank.
NORA recommends that systems be
operated on one pipe whenever possible.
To Check For A Fuel Line Leak:
1. First perform a visual check to look for
signs of fuel leaks along the path of the
fuel line and at the filter.
2. Next verify the fuel unit holds vacuum by
performing the following procedure:
46 National Oilheat Research Alliance
• Disconnect the inlet line and fitting from
the suction port of the fuel unit
• Apply pipe joint compound to a vacuum
gauge and install it into the suction port
• If the unit is connected as a two-pipe
system, remove the return line fitting
and by-pass plug. Apply pipe joint
compound to a plug and install it in the
return port
• Turn on the burner and open the air
bleeder
• Close the bleeder when the vacuum
reaches 15"
• Turn off the burner
• The vacuum should hold for 5 minutes,
if it doesn’t, repair or replace the fuel
unit and perform the same test on the
new or repaired unit
• If the unit holds vacuum, remove the
vacuum gauge, apply pipe joint compound
to the inlet line fitting, reinstall it
and reconnect the suction line
• This process verifies the fuel unit will
hold vacuum, is NOT leaking and is
suitable to use for testing of the fuel line
The following procedure can then be used
to check for a leak in the piping between an
AST and the burner or in the line between the
burner and the shutoff where the line from a
UST enters the building.
3. Shut off the fuel valve at the tank (or wall)
and disconnect the fuel line
4. Connect a “plug” to the disconnected
fuel line
5. Start the burner
6. Once the vacuum reaches 20" turn off
the burner
7. The vacuum should hold for 30 minutes