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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 22021
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I have recently changed my filter on my oil furnace (the

Customer Question

I have recently changed my filter on my oil furnace (the exterior one coming from the tank). I have a R7284B Honeywell controller that was working fine however there is no diagnostic display (LED), so I bought a new R7284U and put it on exactly the same
way. There is no connector to the LIMIT (The R7284B was like that). Anyway, when I turn on (at the thermostat) the emergency heat, I get "No Call for Heat" on the display, it just reads "Standby". I ran through and set all of the installer recommended setting
to make sure they were right. R7284U Installer setup is set as follows: Valve On Delay=0 Ignition Trial=15 Burner Off Delay=0 TT Configuration On=Yes Spark In On Delay=No Spark During Run=Yes Allowed Resets=3 Appliance Type=Furnace Show Diagnostics=Yes What
gives? The R7284B works
Submitted: 1 year ago.
Category: HVAC
Expert:  Rick replied 1 year ago.

I suspect your black lead comes from your furnace limit. What's thrown me off so far is your statement "I have a R7284B Honeywell controller that was working fine however there is no diagnostic display". If you had no line voltage feed besides the limit lead then you don't have an L7284. It's probably an older ignition control that didn't use a hot line in because it had no display. So what you need to do is run a hot feed directly from the 120 v line in for your furnace. How this works is the thermostat calls in the R7284 but the furnace only supplies power (to LIMIT) as long as the furnace plenum temp is under the furnace high limit setting. The new line in is what powers the display. The display is working now because your limit is closed and is hot.

Customer: replied 1 year ago.
Rick,Just wanted to let you know that my oil furnace (ThermoPride) O-5 is running now. Your concern about the Limit switch had me confused since the old R7284B did not have a connector. Whenyou said that the Limit switch (there is one on the R7284U) must be hot I started researching. Anyway I found a Red connector (came with the new controller in the box) and wired it into theblack splice connector, I got power (110vac) and the unit started pumping. All I had to do is prime it. The key also was in the display. There is a way to configure the TT to loop back in the display.I kept seeing the TT configured on, Limit OFF warning.Jim
Expert:  Rick replied 1 year ago.

There is no limit on the R7284 the limit is on your furnace. You don't have it wired right. I've stated several times what the correct way to wire this is. If you don't want to wire this properly there's nothing more I can do for you.