Troubleshooting the HSI (hot surface ignitor or glowbar) type heater
symptom that there is a problem is that the heater will run for 5 seconds
and shut down. Or possibly, the heater will run fine with the top cover removed
but when the cover is replaced the heater shuts down. Generally, this is a sign
that the electronics are functioning properly. Look for and eliminate
all of the SIMPLE problems first.
board/photocell are on board to detect even the slightest flame-out condition or
off-color situation. The system is looking for a ďperfectĒ flame and if
the photocell doesnít see a perfect flame the computer will shut the heater
down. Here are some things to check:
If you brought the heater to
our shop we would immediately check the fuel. If it were suspected that any
other fuel than KEROSENE or DIESEL we would drain the tank and replace with
one of the 2. The photocell/control board safety system does not like NAPTHA,
PAINT THINNER, FUEL ADDITIVES, etc and will shut the heater down if detected-
off color flame.
- Next, we
would immediately check the air pump pressure.
Checking the air pump
pressure should always be the first step in troubleshooting.
The pumped air eventually sucks the fuel from the tank. Low pump pressure
translates directly to poor fuel delivery. Loss of only Ĺ psi
can cause as much as 30% reduction in fuel delivery
performing a pressure check much valuable time is saved in the troubleshooting
process. And, itís easy. For instructions visit
the slightest air leak will cause a loss of pressure. This will cause a flame
discoloration. The photocell will detect it the off-color and will shut the
unit down. Thatís its job.
- If there
is zero psi, then the problem is almost certain to be a broken rotor. But, if
there is ďsomeĒ pressure then the rotor is probably functioning properly, so
adjust the pressure to specs. If unable to reach specs, then look for an air
leak. Finally, if you donít want to check the air pressure- then take the
heater to someone else to fix, because you will never make a heater mechanic!
(No offense intended.) Correct pressure is critical. If you donít have
a low pressure gauge order HA1181 or HA1182 or get one locally, if
available. Our gauges are complete. We have accumulated all of the fittings so
you donít have to go to 3 different stores shopping for the correct
components. This is not a sales pitch! If you donít get ours, get one
- If the
pump pressure is not correct, then set it to the specified pressure using a
low pressure gauge (0-15 psi). NOTE: The computerized heaters are extremely
pressure sensitive. You will be wasting your time to attempt to adjust the
pressure without a gauge.
- For air
leaks at the pump or between the pump and nozzle. Check with soapy water. Stay
clear of electrical components (shock hazard) and the fan blade (knuckle
crack in the black plastic end cover.
Restricted lint filter.
Restricted nozzle. Blow out with compressed air.
or cracked nozzle adapter.
worn. DESA recommends annual replacement. If the pressure is correct and the
heater fires off & runs with the top cover off, but goes out when the lid is
replaced, then itís a 90% good bet that the nozzle is worn. Replace it.
filter restricted. DESA recommends annual replacement.
pickup hose cracked or punctured. The fuel is picked up by suction from the
- Water in
the fuel. You did look in the tank using a flashlight, didnít you? Donít
assume the fuel is free of trash or water- even if you drained & replaced the
- And any
other reason that will affect the flame.
defective ignition control board.
Thermostat models- defective temp control.
problems in the electronics: The photocell & control board can be tested using
an HA1170 diagnostic tester. Most people find that it is more economical to
simply replace the photocell and ignition control board.
understand that my recommendation for trouble shooting comes strictly from the
description that has been given to me over the internet. If your heater was in
our shop, I may have a different evaluation of the problem.
the pump pressure- the first step to troubleshooting
0-15 psi gauge
Part number HA1181
pressure gauge & fittings inserted in the end
cover in order to set the pump to factory specs.
the black plastic end cover that is mounted on the intake end of the
motor/pump assembly. Some end covers are round- some are rectangular. The end
cover will have 2 protrusions, 1 long and one short, and a receptacle that
houses the foam air filter.
long protrusion houses the pump adjuster (relief valve), which consists of a
ball, spring, & adjustment screw. The ball is inserted first, then the spring,
and the screw w/hole. The purpose of the adjuster is to allow excess air to
escape. If the pump is operating properly the further the screw is run in the
tighter the spring & ball, the higher the pressure. Therefore, if unable to
reach or exceed the pressure required for your heater, then there is a problem
ďbeforeĒ the air reaches the gauge, either the rotor is defective or there is an
air leak (the 2 most likely spots to check with soapy water are the cork gasket
that surrounds the lint filter or possibly a crack in the black plastic cover
short protrusion should have a solid plug inserted. Remove the plug- insert the
adjusting screw until the required pressure is reached.
if the pressure canít be reached?
soapy water check for very, lather type, fine bubbles around the lint filter
assembly point and check for a crack(s) in the black plastic end cover. Stop the
leaks and the pressure will come up provided the rotor & vanes are intact, have
the proper gap, and are functional. Of course, the motor must be turning the
Fact...you can replace every part on a heater,--- but if the air pump pressure
is not correct....the heater will not run!!
HSI HEATER FAQ sheet