Quick answer
Code 22 on a Rheem furnace means the main limit or the heat-assisted limit control (HALC) has opened because the furnace overheated. The burners stay off until the limit cools and re-closes, so the furnace protects itself. Replace the filter and open every register. If code 22 returns with a clean filter, or code 61 appears, call a technician: that points to the blower.
Code 22 on a Rheem furnace is an overheat code. Rheem's fault chart for the (-)801 series reads it as “main limit or HALC open”: a temperature safety inside the cabinet has reached its trip point and cut the burners. HALC stands for heat-assisted limit control. Fault charts differ between Rheem series, so match the code against the label on the inside of your furnace door before acting on any chart, this one included.
Is a Rheem furnace safe to run with code 22?
The furnace handles the immediate risk itself. With the limit open, the control keeps the burners off until the limit cools and re-closes, then tries again. Rheem's control also puts a clock on it: if the limit stays open for more than 150 seconds, the control declares blower fault 61 and locks out for one hour.
So an occasional 22 that clears is a warning, and a 22 that keeps coming back is a repair. A furnace that overheats and resets all day heats the house poorly and puts the heat exchanger through expansion and contraction it was not built to repeat. Do not leave it cycling like that for a week.
The safe fix to try first: a new filter and open registers
A limit opens because too little air is moving across the heat exchanger to carry the heat away. Airflow is the part a homeowner can do something about.
- Replace the filter, even if it does not look bad. Hold the old one up to a light; if you cannot see through it, it was choking the furnace.
- Check what you bought. A dense, high-MERV one-inch filter can restrict a furnace as much as a dirty cheap one, as our answer on whether a furnace filter can be too restrictive explains.
- Open every supply register and uncover the return grilles. Shutting off rooms to save heat raises the temperature inside the furnace.
- Confirm the filter is the right size for the slot and its arrow points toward the furnace.
- Switch the furnace power off and on once to clear the code, then let it run a full heating cycle.
Causes of code 22, most likely first
- A clogged or over-restrictive filter. It is the simplest cause and the first to rule out.
- Closed or blocked registers and returns: furniture over a return grille, a finished basement with the supplies shut, rugs over floor vents.
- Restricted ductwork or a dirty air conditioning coil. The cooling coil sits above the furnace in the supply air, and years of dust on its underside block air the same way a filter does. In 1950s and 60s bungalows the original ducts were sized for a different furnace and can be too small for the airflow a newer one needs.
- A blower that is not moving air: a failing motor, a wheel caked with dust or the wrong speed setting. This is where code 61 comes in.
- A limit that has weakened after many trips and now opens early. It is replaced only after the airflow has been proven good.
What codes 22 and 61 together tell a technician
Code 61 after a 22 means the limit did not re-close inside 150 seconds, which the control reads as a blower that is not doing its job. That shifts the diagnosis away from filters and toward the motor and wheel. If the display shows 61, or the furnace is sitting in its one-hour lockout, book the visit instead of resetting.
On site, the technician measures temperature rise: the difference between the return air going in and the supply air coming out, compared against the range printed on the furnace's rating plate. A rise above that range confirms low airflow, and static pressure readings on each side of the blower show whether the restriction is the filter, the coil or the ducts. Gas pressure is checked as well, since an over-fired furnace overheats even with good airflow.
What a code 22 repair costs
- Diagnostic visit: $90–$150, folded into the repair.
- Most furnace repairs: $150–$800.
- Blower motor replacement: $500–$1,500 depending on the motor type.
- Furnace tune-up with a blower and airflow check: $120–$250.
A limit switch replacement is quoted on site once the technician has confirmed that the switch, and not the airflow, is at fault. Duct changes are quoted separately and in writing.
Call when 22 returns with a clean filter and open registers, or as soon as 61 shows. ZK Mechanical's TSSA-licensed technicians handle furnace repair from the Burlington shop across Halton, Hamilton and the west GTA: (647) 801-1252, or book through the contact page. The Rheem furnace error code guide lists the neighbouring codes, and code 57 covers the pressure switch fault.