Dettson OLR098A12A, Installation Instructions And Home Owner'S Manual

 10

CAUTION

Low flue gas temperature increases the risk of 
condensation. Adjust the total flue gas temperature 
at or higher then 204°C (400°F) in order for the heat 
exchanger warranty to remain in force. 

3.3.5 

O

VERFIRE PRESSURE TEST

 The overfire draft that is taken through the observation port, 
located above the burner, is a measurement necessary to 
determine if there is a blockage in the heat exchanger or the 
flue pipe. Refer to the Technical Specifications in this manual 
for overfire pressure values. A high pressure condition may be 
caused by excessive combustion air, due to the air band being 
too wide open, or a lack of flue draft (chimney effect) or some 
other blockage, such as soot in the secondary section of the 
heat exchanger or the use of an oversize nozzle input or high 
pressure pump. 

3.3.6 

V

ENT 

T

EMPERATURE 

T

EST 

1. 

After having adjusted the burner combustion, insert a 
thermometer into the test hole in the breech pipe; 

2. 

The total vent temperature should be between 204 and 
302°C (400 and 575°F). If not, check for improper air 
temperature rise, pump pressure, nozzle size or a badly 
sooted heat exchanger.  Also refer to section 2.5 for 
proper flue pipe sizing. 

3.3.7 

S

UPPLY AIR 

T

EMPERATURE 

R

ISE 

T

EST

1.  Operate the burner for at least 10 minutes; 
2.  Measure the air temperature in the return air plenum; 
3.  Measuring the air temperature in the largest trunk coming 

off the supply air plenum, just outside the range of radiant 
heat from the heat exchanger. 0.3 m (12") from the 
plenum of the main take-off is usually sufficient; 

4.  The temperature rise is calculated by subtracting the 

return air temperature from the supply air temperature; 

5.  If the temperature rise is lower or exceeds the 

temperature specified in Table 1, p. 13, change to the next 
lower or higher blower speed tap, until the temperature 
rise falls to the target. If the excessive temperature rise 
cannot be increased or reduced by changing fan speed, 
investigate for ductwork obstructions, dirty or improper air 
filter, improper firing caused by improper pump pressure 
or nozzle sizing. 

3.3.8 

L

IMIT 

C

ONTROL 

C

HECK

After operating the furnace for at least 15 minutes, restrict the 
return air supply by blocking the filters or the return air register 
and allow the furnace to shut off on High Limit. The burner will 
shut off but the blower will continue to run. 

Remove the obstruction and the burner should restart after a 
few minutes. The time required for the restart also depends on 
the adjustment of the blower “OFF” delay. 

3.3.9 

R

ESTART AFTER BURNER FAILURE

1.  Set the thermostat lower than room temperature; 
2.  Press the reset button on the burner primary control 

(relay) 

3.  Set the thermostat higher than room temperature; 
4.  If the burner motor does not start or ignition fails, turn 

off the disconnect switch and CALL A QUALIFIED 
SERVICE TECHNICIAN. 

CAUTION

Do not attempt to start the burner when excess oil has 
accumulated, when the furnace is full of vapour or when 
the combustion chamber is hot. 

4 MAINTENANCE 

WARNING 

Electrical shock hazard. 

Turn OFF power and fuel to the furnace before any 
disassembly or servicing. 

Failure to do so can result in death, bodily injury 
and/or property damage.

Preventive maintenance is the best way to avoid 
unnecessary expense and inconvenience. Have your 
heating system and burner inspected by a qualified 
service technician at regular intervals.  

To maintain the reliability and optimal performance of the 
furnace, have a complete combustion check done after 
the annual maintenance call. Do not attempt to repair the 
furnace or its controls. Call a qualified service technician. 
 

Before calling for repair service check the following points: 

1.  Check the oil tank gauge and make sure that the 

valve is open; 

2.  Check fuses and the circuit breaker; 

3.  Check if the main disconnect switch is ON ; 

4.  Set the thermostat above room temperature; 

5.  If ignition does not occur, turn off the disconnect 

switch and call a qualified service technician. 

When ordering replacement parts, please specify the 
complete furnace model number and serial number.