Archive for the ‘furnace maintenance’ Category

What is a limit switch and why does it shut off my furnace?

April 25, 2011

What is a limit switch and why does it shut off my furnace?

Trane SWT 01635 thermal limit switch,

photo of item KSS#72-092

The limit switch is a small, silver bi-metal disc about the size of a dime or quarter which turns off the furnace if the temperature inside the furnace gets too hot (see another example)  It is a safety device and should not be disabled or bypassed.  Limit switches do go bad sometimes, especially if the furnace routinely overheats.  However, you should try to determine why your furnace is getting too hot before you replace the switch.  An overheated furnace is usually the result of inadequate air flow through the furnace or a furnace that is too large for the building.  An overheated furnace is not only inefficient, it will shorten the life of the heat exchanger in the furnace.

The first thing to check is your registers.  Make sure all registers are open and not blocked by furniture or other items.  Be sure the filter in the furnace is clean.  If you have recently added air-conditioning to your system, it may be possible to increase the blower motor speed.  Get a furnace technician to do this if you are unsure how to safely change the speed.

If you have tried all of the above and replaced the limit switch but the furnace still overheats, the size of your ductwork or furnace is suspect.  Do you have at least as much cold return air coming back to the furnace as there is warm air going to the home?  If not, add more cold air runs or increase the size of existing runs.  You may also need more warm air runs to get the heat away from the furnace.  The main trunk or ductwork may be too small to handle the needed air flow.  Call a trusted HVAC technician to do a heat loss and/or heat gain assessment for your house to see if the ductwork and furnace are properly sized.

More information can be obtained at the links below:

More about high limit switches at

Interesting forum entry regarding limit switch on


With Oil Nozzles, size does matter

March 24, 2011

Can I Change the Size or Type of My Oil Nozzle?

In general, the oil nozzle recommended by the heater manufacturer should be used.  This can usually be found on a tag on the heater.  The nozzle is rated by GPH (gallons per hour of fuel use), spray angle and spray pattern.  For example, a .60 80 B nozzle will deliver .6 GPH oil use with an 80 degree angle and solid spray.

You may experiment with a smaller GPH nozzle to achieve better fuel economy.  A 1.20 GPH nozzle may be replaced with a 1.10 GPH, etc.  You may also try using a “W” nozzle in place of a hollow (A) or solid (B) spray pattern.  Other changes, especially to the spray angle should be left to an experienced technician.

More information can be found on the links below:

“Total Look at Oil Burner Nozzles”- by Delavan

Oil nozzle size–effect on consumption – Gardenweb discussion group

Nozzle sizes are stamped on the nozzle: – forum

When you purchase oil nozzles from our web site, in order to keep shipping costs low, we ship them using  US Priority mail.  Please provide a valid mailing address when you place you order.

Suntec Oil Pump Strainers

March 24, 2011

Suntec Oil Pump  Strainers

Checking the strainer in your fuel pump should be part of the routine annual maintenance of your oil furnace or boiler.  It should also be checked if you are not getting a good oil flow at the nozzle or you have pulsating pressure.  To check the strainer, remove the four screws on the front cover with a 5/32 Allen wrench.

Suntec Pump




strainer for Suntec Pump





You can clean the strainer with a brush and clean fuel oil or replace it with an inexpensive new strainer.  Look at the first letter of the Suntec model number to determine the right strainer.  There are different strainers for the A-series, B-series and J or H-series pumps.

For more information:

Suntec Field Service and Trouble Shooting Guide

Oil Nozzle – Care

March 23, 2011

Oil Nozzle Care and Tips

Oil nozzle wrench next to electrods

Delavan Oil Nozzle Changing wrench

Oil nozzles are designed to do an accurate job of atomizing and metering fuel oil in the spray pattern of your burner. Keep nozzles in their original containers. Handle the nozzle by the hex flats and avoid touching the strainer. Use clean tools.



Using oil nozzle wrench to remove oil nozzle
Using the oil nozzle wrench


We recommend using a Delavan nozzle changer wrench to protect the porcelain electrodes.




Using box end wrenches to remove oil nozzle

using box end wrenches



If you do not have a nozzle changer wrench, you may also use two box-end wrenches.



Nozzles and oil filters should be changed at least annually for optimum service and efficiency. Add a good fuel oil treatment (our item number 47-330) to your oil tanks every year to keep filters and nozzles free from sludge and water.


We do not recommend trying to clean and reuse nozzles.  It is better to keep a spare on hand during the heating season.

Other information can be found below:

Adjusting Electrodes

March 22, 2011

How do I adjust my electrodes?

Adjusting electrodes in your oil burner is something normally done by a professional, however it is not rocket science.  If the homeowner is capable of doing most home repairs, he/she can adjust electrodes.  The standard cautionary  notes apply:  make sure you turn off the system, and be careful because you are working around fuel oil.   Make sure you don’t over-tighten the holder, you do not want to crack the porcelain.   If you do not feel comfortable, defer to a professional.

loosing the electrode adjustment screw

loosen the adjustment screw




1.  Use a wrench or screwdriver to loosen holder to adjust or position electrodes.





Setting the gape between the electrodes tips

setting the gap between the tips





2.  Set gap at 1/8″





Setting the electrode 1/8" forward of the nozzle tip

setting electrode tip 1/8" forward of nozzle tip



3. Set electrodes 1/8” forward from end of  nozzle.





Setting electrodes up from nozzle center 1/2"

Setting electrodes 1/2" up from nozzle center







4. Set electrodes about ½” from center of nozzle to center of electrodes.

showing use of electrode setting gage

using electrode gauge







You may also use a gauge. Our # 66-105






Lastly, don’t forget to tighten the adjustment holder nut you loosened in step 1.


The table below shows some nozzle setting recommendations

Nozzle degree GPH Figure (2) Figure (3) Figure (4)
45 .75 to 4.00 1/8” to 3/16” ¼” ½” to 9/16”
60 .75 to 4.00 1/8” to 3/16” ¼” 9/16” to 5/8”
70 .75 to 4.00 1/8” to 3/16” 1/8” 9/16” to 5/8”
80 .75 to 4.00 1/8” to 3/16” 1/8” 9/16” to 5/8”
90 .75 to 4.00 1/8” to 3/16” 1/8” 9/16” to 5/8”

If above 4.00 GPH you may need to increase Figure (3) by 1/8” to enable smooth startup.

We list many common electrodes on our website.

How often should I change my Air Filter?

March 15, 2011
The standard 1” air filter is factory stamped as a 30 day filter. Although thisstandard 1" furnace filter may seem a bit overboard the concept is very sound. Both Heating & A.C. units need to move air in order for them to work easily and efficiently. A plugged filter could result in costly repairs that can easily be avoided with some routine maintenance. Change your filters regularly!!! 

More interesting information can be seen on the links below:

How to change your filter –

Home Inspector finds a home with no filter in it.  – Home inspector blog

The average person breathes in about 32,000 pints (18,185 liters) of air per day. Those 32,000 pints contain about 1,120,000,000 particles of dust –

We carry many of the  common furnace filters sizes on our website