Suburban furnace - no spark issue

[kameronth]

I have a 2010 Gulfstream TT. I tried searching the forums but majority of the issues I found were for no ignite problems.

My issue, I have no spark at all. The fan turns on under normal operation of the thermostat but the igniter does not attempt to spark - to simplify, it does not "click" at all.

Where/what should I check first? Should I remove the whole unit or are there test I can perform while it's still in place? The unit is a Suburban SF-xx - I'm not sure of the exact model number until I crack the unit open. Thanks.

[kameronth]

I took off the electrical connections to both the sail switch and limit switch, cleaned the connections and put a little electrical grease on them. That did the trick. It ignites and blows hot. Thanks for the help!

[Boon_Docker]

Deleted double post

[Boon_Docker]

My bad, you're correct.

[Chris_Bryant]

Boon Docker wrote:

kameronth wrote:
Thanks for the tips. I should add, we went camping last labor day and the furnace worked fine the first night, then stopped the second. My stove has good propane flow and so does my hot water heater which is further down the gas line than the furnace.

I'll check the limit switch tonight. Can the sail switch be cleaned without removing the unit?

If the fan is running like it should then the sail switch is OK and does not need cleaning.

The only way a bad sail switch will keep the fan from running is if it is stuck closed. The fan will run fine with a sail switch failed open.

[Boon_Docker]

kameronth wrote:
Thanks for the tips. I should add, we went camping last labor day and the furnace worked fine the first night, then stopped the second. My stove has good propane flow and so does my hot water heater which is further down the gas line than the furnace.

I'll check the limit switch tonight. Can the sail switch be cleaned without removing the unit?

If the fan is running like it should then the sail switch is OK and does not need cleaning.

[Chris_Bryant]

That's it- the vents can tend to hold the door in place- they are a slip fit over the furnace exhaust and intake. If you remove the screws and jiggle the door to slip the vent off it usually works.

[kameronth]

This is the best picture I could find. Is this the door you are talking about with the exhaust vents? I tried removing the screws before but the whole latch appears to be glued in place and I was afraid of bending the metal when I was pulling on it.

[Chris_Bryant]

If your has an outside door it is fairly easy to access the sail switch- it will be right there when you remove the door. If you don't have an outer door, it has to be removed.

[kameronth]

Thanks for the tips. I should add, we went camping last labor day and the furnace worked fine the first night, then stopped the second. My stove has good propane flow and so does my hot water heater which is further down the gas line than the furnace.

I'll check the limit switch tonight. Can the sail switch be cleaned without removing the unit?

[RoyB]

Mine get debris in the sail switch quite often since it is on the floor and we have animals wandering around... The fan is working to blow against the sail switch. In the event the fan shuts off the furnace propane feed needs to shut off as well so this sail switch is the feature that controls that...

The other problem may be no propane flow. You can check this by lighting up the stove top and see if it is burning a good blue color flame...

I have had problems on occasion where I opened the propane value to quickly and it has a pressure valve that will sometimes shut off when this happens resulting in no propane flow... Have to close the value again and wait a few seconds then open slowly which usually works then...

I have two propane tanks on my trailer so I have a d-ring that I move to the propane that is running. Then old me sometimes forgets what the d-ring means - to use or is this tank empty (I need to add a note) hehe... Gotta love getting old hehe...

Roy Ken

[Chris_Bryant]

On the SF series, I have found the most common failure is the limit switch- if you open the inside panel (not outside), it is right there. Often simply unplugging and replugging the leads will fix it, due to oxidation on the terminals. Next is sail switch.

Sequence of operation-

• Thermostat calls for heat
  
• relay (or board) starts blower
  
• sail switch closes at ~75% speed
  
• board gets power- ~30 second purge cycle
  
• board fires spark and opens gas valve for ~7 seconds
  
• etc
  

[donn0128]

Gas flow is first. Then the sail switch.