oil warm air furance

plumb9646

Customer has a new 2 years old oil furance that seems to short cycle runs for 2-5minutes and turns off then 10-20 minutes later it is on again . It has a old honeywell programable theromstat,I think that is the problem .

David_5

cycle rate

The cycle rate needs to be changed so that the furnace cycles properly.

David

Tony_8

It's probably

just oversized. Check the current firing rate and the rating plate and see if it can be downfired.

If you're not sure how to do this properly, call someone who is. Not as simple as it sounds and great trouble will follow if not done correctly.

Weezbo

ok so .....how about testing that idea ....

go to burner turn the power off take the primary tt wires off wire a small piece of #14 16 18 whatever wire t t together with a wire nut on the primary put the wire that was there aside with a wire nut on one of the wires and turn the burner back on.if it isstill cycling it aint the t stat.

Weezbo

then the next place to look is the fan limit switch....

turn the powere off push it in and twist it all the way right a couple times.make sure its clicking where its supposed to...

Jack_21

Is it cycling on the limit?

Inadequate air flow makes the hi-limit an operating control. Is the filter packed? I use a Dwyer100-5 for draft tests and also for checking the duct sizing. Very acurrate. You can read both the SA and RA with it and find restriction in the duct. I guess I should explain that. Here goes.

The rating plate on the furnace will give a total static number typically .5". Take the probe (connected to the +pressure side)on the dwyer and put it into the SA duct work right at the duct connection, perpendicular to the air flow and note the reading. Let's say it is .2" On the RA (which in my experinece is the most likely culprit)insert the probe on the duct side of the filter and note reading. Pull filter and duct tape opening and do it again. Lets say you have +.2 on the SA and on the RA you have -.7. Drop the + & - and add the numbers giving you .9. Way above the .5 spec'd. Move away from the furnace on the RA side to the next fitting and meausre upstream of that fitting. Still -.7, go further back up the duct. The vast majority of these I have seen have the restriction on the RA drop. Put it up there and if that is the problem the neg side static will drop to the max total static of .5. I think you can use a Testo or UEI differencial pressure gauge also. I've had the Dwyer for about 20 yrs and it is a great instument giving 1" draft or perssure.

jeff_51

ya know

we ran into a furnace once where the cust was using loads of fuel to heat a small house, short cyceling all the time (can't spell). The cust had never, and I mean never, chaged the filter. In TWENTY and I mean TWENTY years. Took me half hour to pull out the "filter" or what was left of it and all the junk. I'm sure you checked this already, but you never know what you will find.