Gas Furnace Unexpectedly Turns Off

[kjpro]

18 x 22 return duct is adequate....

The unit calls for a 16 x 25 filter...= 400 sq inches He has a 18 x 22 filter...= 396 sq inches (close enough)

[kjpro]

1400 cfm = about a 60 degree delta (specs for the furnace is 40-70) 1400 cfm = about a 10 x 24 return duct. (.08) (grill size is of coarse bigger then that)

[kjpro]

Minimum return filter for this furnace is 16 x 25 = 400 sq inches He has a 18 x 22 = 396 sq inches

1400 cfm with a delta of 60 = 10 x 24 duct

I felt the delta T was to high before the pictures. (and may still be, not knowing the whole ducting system) But, after the pictures there are install issues too.

Yes, this is where most of the problems lie, I'd like to know what the Manuel J says the home calls for. (probably not 100K beings the # of supply registers, but none of us can see his home)

But, that furnace is *not* installed correctly. (will post it all in a new post)

[kjpro]

Units specs are:

91,000 btu output 40-70 delta T 1400 cfm blower 16 x 25 filter

[Radu Tenenbaum]

hours...have

If it's an overheating condition, can that be alleviated by changing (increasing) the blower speed? It's adjustable on the furnace.

I appreciate everyone's contributions. I'm just the homeowner and have never had to deal with HVAC issues, but I'm an engineer and understand systems in general. I added central air and, at the same time, changed my very old furnace last summer. I'm trying to get as much information as I'm apparently having to deal with an installer/tech whose competence may not be of the highest level.

Radu

[kjpro]

I say this furnace has multiple problems causing the furnace to intermittently cycle the burners.

a. over heating "temp rise" b. venting & combustion piping (minor) c. draining issues

Further explanation: (per instructions)

a. Temp rise is to be with-in 40-70 degrees (blower @ mid-hi.."which it's on", will flow at 1209 cfm @ .1 ESP .....to give a delta of 69...."max rise right there", and I'd be suprised if your running at .1 ESP)

b. Venting requires DWV long radius 90 to be used. 1. to extend 8" minimum past structure. 2. no 45 on outside flu pipe 3. move decking boards....it's recycling the flu gases

c. Draining issues: 1. hoses need slope to trap assembly 2. trap assembly needs vent hose to transition assembly 3. cut hoses to length

**********

Questions:

a. Did the installing company run a Manuel J & D on your home? (it may not require the 100K Btu. furnace...)

b. Supply Trunk measurements? c. Supply laterails...sizes? (15.....3 are off....what's left...12-6"??) (flex off off plenum....8"??)

d. Return grill sizes? e. Coil box used? or coil installed in plenum? f. Water on bottom shelf.... (flu coupler leaking?)

g. What's the temp rise?

**********

Comments:

a. Furnace on concrete (will rust bottom) b. No vent/clean-out on evap coil drain. c. Duct tape on plenum box (run out of foil?) d. Insulation on bottom of supply duct (needs taped...3-5' in front of furnace) e. Suction tubing for evap coil needs insulated (will drip on furnace) f. Duct tape on left side of furnace, why? (plug should stay by itself) g. Move electrical junction box behind on/off switch h. Re-caulk vent/comb piping

**********

Conclusions:

1. tripping on limit
2. drain issues

1. run manual J & D

side note: extend pop-off on water heater

Good Luck.

[kjpro]

Setting the blower to HIGH will help. (won't solve all the issues though)

New post is posted with all my comments.

Your Welcome, Keep us posted, as to what transpires. :-)

[Radu Tenenbaum]

Thank you very much for taking the time to address this.

This morning the furnace stopped after running 15 minutes. Restarted after five minutes and then shut off 15 minutes later and then restarted after 5. During the two five minute off periods, I opened the side panel and looked at the gas valve diagnostic lamp. In both instance is was flashing 6 and 2, which according to the manual is "Soft Lockout - Maximum recycle count exceeded - Last failure was Flame Sense lost during run".

As to the issues you identified:

1. From my reading (and re-reading) the install manual, I also concluded that the drain tubes to the condensate trap were too long and not maintaining the down angle. Also, as you indicated, the vent tube between the condensate trap and the plastic transition box is missing.

1. The duct tape was my handywork. I applied it over the silver aluminum tape the installers had used that was not staying stuck.

This gives me good information to discuss with the technician.

Once again, thank you for your time.

Radu

[Sniper]

Why not put a meter to measure where the cut off is? An open circuit should read about 24vac, if the circuit is 24vac. Check all the sensors and induce fan switch. Once the open circuit is found then check why it caused to open. Guessing is not a way to find it. We are not next to the unit.

reguads

[Radu Tenenbaum]

Here's an update. Technician showed up this morning and replaced ignitor/flame detector module. I cooled down the house (opened doors, ran whole house fan) and ran the furnace for one hour and ten minutes. It never shut down. Earlier in the morning, before the technician came, it would not run for more than 15 minutes. That's a good sign. I'll keep watching and monitoring.

Radu

[kjpro]

Did you have him address the other issues? (like the vent hose, cut hoses to length, remove the dip in tubing)

Did he change the blower speed? Did he check the temp rise?