oil fired warm air furnace problem

nugs

First of all, I'm not a crotchity ol timer, I just happen to hate the newer solid state fan timers, they suck. Here's a quick, lasting and effective fix. Install a honeywell 4064B fanlimit in the plenum and by pass the blower and limit controls. Old school but it works every time. For those of you doing burner service, and you don't have a control board for every damned furnace made. Keep a 4064 on the rack and when the board dies in the middle of the night you can give them heat again

ddenny

oil fired warm air furnace

I have a customer with a rheem warm air oil fired furnace that seems to run fine for a while but eventually cuts off on heat high limit. the limit is one of those little disc things about the size of a dime. it sticks into the heat exchanger a couple of inches. I replaced one disc which burnt up at the spade connection. I discovered the fan delay timer was defective and wasn't letting the blower come on so I figured that's why the high limit broke. I installed a new run and thought everytihing was ok but the high limit started opening again. filter is clean but I suspect the heat exchanger may be partially blocked thereby not letting enough air flow over the heat exchanger. what else could it be. how would I check for a blocked heat exchanger. temperature difference maybe? or how bout checking the air velocity? any ideas?

Mitch_4

NUGS

While I agree to some extend about FTBs suck, what you are proposing will completely void warranty, and should ANY accident happen, you are liable, because you essentially built your own furnace, and it is not a certified appliance.

In addition, snap disc limit holes are close to the H.E. a probe type will not fit. In addition there are standards as to where a limit must be and how it must operate..(max air delta T 100°,m max heat exchanger temp 1100°) there is no way you can meet those design standards (ULC stds) in the field with that fix.

Now as to my limited agreement. Application and design makes all the difference. Some are so poorly designed they will fail, others are well done so they last. I do a lot of FA, and I have my preferences, used em for 16 years, they went FTB on some models, but well thought out, and 0 issues to date fr me.

In the OP case sounds like the heat rise wasn't set. The blower should be adjustablke in its speed either by being a multi tap direct drive, or has an adjustable motor pulley. Measure the heat inthe return duct, and the air leaving the plenum. Do the second about 12-18 inthe main trunk. DO NOT do it in the plenum itself as radiant heat will affect the read. (The factory tour I took streesed this as that is how it is tested and certified in the lab)

Compare against the rated heat rise on the rating plate. either increase or decrease the motor speed to get it in the range stated on the plate.

Also look at the manual. If you added A/C, some mfg require a smaller blower pulley to accomodate the increased static pressure from the coil.

Good luck