Service Facts
Handling Seized Fuel Units
For about 10 years, there have been reports of
seized fuel units with brown varnish type deposits
on the gears and shaft of the fuel unit. Typically,
the technician changes the bound fuel unit, and the
situation reoccurs—unfortunately, often repeatedly.
Fuel units do not normally bind unless contaminated
by degraded fuel or other foreign substances. The
underlying cause needs to be determined and rectified
before changing the fuel unit, otherwise the new fuel unit
will also fail, increasing service costs and diminishing
customer satisfaction.
Water in the fuel tank is a primary source of these
issues. Therefore, good tank housekeeping practices are
critical. It is good practice to check for the presence of
water in storage tanks at every maintenance visit and
is mandatory when confronting a bound fuel unit. Check
tanks for water and remove it, then determine the entry
point. When it comes to water buildup in the system,
areas to be aware of are:
• Missing fill or vent caps
• Rotted fill or vent piping
• Condensation, particularly with outside tanks
• Broken tank gauge vials with outside tanks
• Failing to drain water from new tanks at
installation
Bob O’Brien
Director of Education
National Oilheat Research Alliance
• Pumping contaminated fuel from an old tank to
a new tank
• Tanks must be pitched toward the bottom
outlet by ¼" per foot.
• Outside tanks need a manufacturer-approved
means to drain water from tank
• Do not use TeflonTM or other similar tape
• Check filter canisters for corrosion and replace
them if necessary
• Replace spin-on filter cartridges that have been
exposed to water
Manufacturers and NORA (National Oilheat Research
Alliance) have conducted extensive testing on fuel samples
from affected sites as well as the seized pumps themselves.
The failure modes fall into two categories, water-induced
corrosion (Figure 1) and sticky polymers (Figure 2).
Removing and eliminating the sources of water resolves
fuel unit corrosion issues.
Degraded fuel that forms polymers should be approached
differently. Biodiesel content is sometimes
blamed. Sticky residues occur with no biodiesel content,
as well as with biodiesel. There is also no correlation with
the delivered fuel itself. Sites that received deliveries on
the same day and from the same truck do not show these
Figure 1 Figure 2
14 ICM/November/December 2022