Rheem Furnace Won't Ignite: Causes, Fixes & Costs
Get this fixed by a local pro
Free, no-obligation quotes from licensed HVAC technicians in your area. Compare up to 3 estimates before anyone visits.
Rheem furnace won't ignite: what it means
“Won’t ignite” describes a Rheem gas furnace that runs through its startup sequence — the inducer motor spins up, the pressure switch closes, and the board calls for ignition — but the burners never light or the flame is never proven. After a set number of failed trials, the control board declares an ignition lockout and shuts the gas valve for safety.
On most Rheem furnaces this is a soft lockout: the board attempts ignition roughly three times, then locks out and typically auto-retries after about one hour. Some boards hold in lockout until power is cycled. The exact trial count and retry timing depend on your control board generation, so confirm against the wiring diagram or troubleshooting label inside the blower door.
This is a pro-level problem. Every likely fix lives inside the cabinet — the igniter, flame sensor, burners and gas valve are all technician territory.
Rheem furnace won't ignite: common causes, ranked by probability
- Failed or cracked hot surface igniter (HSI) — The most common single cause. The igniter glows to light the burners; a cracked or aged element won’t reach ignition temperature.
- Dirty or failed flame sensor — The furnace may light briefly then shut down because the board can’t “see” the flame. Oxidation on the sensor rod is extremely common and easy to miss.
- Gas not reaching or lighting at the burners — A failed gas valve coil, a valve that isn’t opening on command, or a fouled burner assembly means the igniter glows but the burners never light. (Broader gas-supply faults are usually reported as separate flame/ignition-failure codes.)
- Weak or intermittent ignition control / board fault — The integrated furnace control isn’t sequencing or holding the gas valve open correctly.
- Wiring, connector or ground problems — Loose flame-sensor ground or corroded connectors cause false “no flame” readings.
Rheem’s own troubleshooting flow generally has a technician confirm the igniter glows, then verify the flame is sensed — which is why HSI and flame-sensor issues top this list.
How to fix Rheem furnace won't ignite: safe checks first
If you smell gas — a rotten-egg or sulfur odor — stop here. Leave the house immediately, don’t touch light switches, thermostats or the furnace breaker, and don’t use your phone indoors. Call your gas utility’s emergency line or 911 from outside or from a neighbor’s home. Do not go back in until they tell you it’s safe.
Otherwise, these are the only steps a homeowner should perform:
- Thermostat: Confirm it’s set to HEAT with the setpoint above room temperature. Replace the batteries if it’s battery-powered.
- Air filter: A clogged filter can trip safety limits and interrupt startup. Replace it if it’s dirty.
- Breaker / power switch: Check the furnace breaker and the on-unit service switch. If tripped, reset it once.
- Supply and return vents: Make sure registers are open and unblocked so the system can move air.
- Condensate line (high-efficiency models): If the drain is clogged, a full condensate trap or float switch can block ignition. Clear a visible blockage if you can reach it safely.
- One reset: Cycle power at the breaker once and let the furnace attempt a full startup. If it locks out again, stop — do not repeatedly reset a locked-out unit.
If ignition still fails, call an HVAC technician.
How a technician will diagnose it
A qualified tech will typically:
- Read the fault/flash code on the control board LED to confirm ignition failure vs. lockout.
- Watch a full ignition sequence: inducer start, pressure switch closure, igniter glow, gas valve opening, and flame sensing.
- Test the hot surface igniter for continuity/resistance and inspect for cracks.
- Measure flame-sensor microamps and clean or replace the sensor rod.
- Check gas valve voltage and operation, and verify manifold gas pressure.
- Inspect wiring, grounds and connectors at the board, valve and sensor.
- Confirm the burners are clean and firing evenly.
If a technician quotes a gas valve or board without first checking the igniter and flame sensor, ask why — those two parts explain the majority of these calls.
Symptom, cause and what to do
| Symptom | Likely cause | DIY action | Technician job |
|---|---|---|---|
| Igniter glows, no flame | Gas valve or dirty burners | Try one reset | Test valve, check pressure, clean burners |
| Fires briefly, then shuts off | Dirty flame sensor / bad ground | None safe | Clean or replace flame sensor, fix ground |
| No glow at all | Cracked hot surface igniter | Confirm power & filter | Test and replace HSI |
| Clicks, then locks out | Failed ignition sequence | One reset only | Full sequence diagnosis at board |
| Repeated lockouts after 1 hr | Board or wiring fault | Stop resetting; call pro | Test control board and connectors |
| No startup at all | Power, thermostat, filter | Check breaker, thermostat, filter | Diagnose power/limit circuit |
Rheem furnace won't ignite repair cost
Honest US ranges (parts + labor):
- Reset / filter change: $0 (DIY)
- Flame sensor clean or replace: $80 – $250
- Hot surface igniter replacement: $150 – $350
- Gas valve replacement: $300 – $650
- Integrated control board: $400 – $1,200 (two-stage and variable-speed boards land at the high end)
- Diagnostic / service call: $90 – $180 (often credited toward the repair)
Prices vary by region, furnace age and parts availability. On older Rheem furnaces, ask about total repair cost versus replacement if multiple major parts are failing.
Related codes
- Rheem Furnace Pressure Switch Fault — inducer or venting-side faults that stop the sequence before the board ever calls for ignition.
- Rheem Furnace Flame Sense / Flame Loss — for a furnace that lights and then drops out on flame-proving rather than failing to light at all.
- Rheem Furnace Limit Lockout — high-limit trips from restricted airflow, often traced to a clogged filter or blocked vents.
This page covers the general “won’t ignite / ignition lockout” condition; if your board reports a dedicated flame-failure, pressure-switch or limit code, follow that fault instead.
Parts & tools for this fix
As an Amazon Associate, fixme.vip earns from qualifying purchases. Prices and availability are on Amazon.
Frequently asked questions
Will my Rheem furnace reset itself if it won't ignite?
Most Rheem boards attempt ignition several times (typically 3 trials), then enter a hard lockout. Many auto-retry after about one hour, but the count and timing vary by control board — check your unit's label.
Can I fix a Rheem furnace that won't ignite myself?
You can safely swap the filter, check the thermostat and breaker, and try one reset. The igniter, flame sensor, gas valve and wiring are inside the cabinet and are technician-only jobs.
How much does it cost to fix a Rheem furnace that won't ignite?
A cleaned or replaced flame sensor can run $80–$250, a new hot surface igniter $150–$350, a gas valve $300–$650, and an integrated control board $400–$1,200 depending on whether the furnace is single-stage, two-stage or variable-speed. A simple reset or filter change costs nothing.
Why does my Rheem furnace click but not light?
Clicking often means the board is calling for ignition but the igniter isn't glowing or the flame isn't being sensed. Common causes are a cracked hot surface igniter or a dirty flame sensor — both need a technician.