Understanding Intermittent Two-Blink Fault Codes
Codes
The Lennox and IHP Winslow PI40 and PS40 pellet stoves use three Ready Light fault codes related to the safety circuit:
At first glance these codes appear straightforward. In practice, however, they are surprisingly difficult to interpret. The difference between the long/short blink pattern and the two short blink pattern is subtle enough that many technicians and homeowners cannot reliably distinguish them during operation. Likewise, unless you’re familiar with each pattern, how does one know if two identical blinks in succession are in fact long or short? Long or short compared to what? You’re only getting one fault. As a result, troubleshooting often begins with the wrong component.
The confusion becomes even greater when each suspect switch tests perfectly. A typical service call begins with the stove displaying a fault approximately one second after the Start button is pressed. The immediate assumption is that one of the safety switches has failed.
The high-limit switch is inspected first. The manual-reset button has not tripped, the switch is closed, and continuity is present. The switch is operating normally.
Attention then turns to the vacuum switch. Applying approximately 0.10 in. W.C. of vacuum closes the contacts, continuity is present, and the diaphragm successfully holds vacuum. Again, the switch tests normally.
Finally, the proof-of-fire switch is tested and also operates exactly as expected.
At this point every component identified by the fault codes has passed testing, yet the controller continues reporting a safety circuit failure.
What Is Actually Happening?
Unlike many pellet stove control systems that simply monitor whether an individual safety switch is open or closed, the Winslow controller appears to evaluate the electrical characteristics of the entire safety circuit. It could have monitored everything with dedicated circuits, but that would have required more wires and more copper. Country Stoves, the original manufacturer of this problematic child, evidently thought they were going to sell 1,000,000+ units, and instead of having 12 wires coming off the control board, they opted for the bean-counter method of only nine wires.
The vacuum switch and proof-of-fire switch each have their own signal wire, but they share a common return conductor back to the control board. Likewise, the high-limit switch is wired in series with the auger feed motor and ultimately shares common return paths with other stove components.
To further complicate matters, after Country Stoves sold to Lennox, and later after Lennox sold the line to IHP, a hopper lid switch was introduced. This switch utilizes a resistor to simulate the presence of the auger motor in the circuit so that stove owners could open and close the hopper lid while the unit was running without triggering a shutdown fault.
As a result, the controller is evaluating more than the individual switch itself. It is effectively evaluating the entire circuit path, including:
Each of these conditions can increase total circuit resistance while the switches themselves continue to function normally.
This explains why a switch can pass every continuity test performed with a multimeter yet still generate a startup fault code.
Recommended Repair
If the fault is generated immediately at startup, this should be your first clue. If a fault were generated while the unit was already running, I would focus my attention on the individual switch identified by the corresponding fault code.
Your next clue is this: if all of the safety switches test correctly, but the stove consistently generates an immediate startup fault, suspect deterioration of the wiring harness before condemning the control board.
In my 25 or so years of working exclusively on pellet appliances, I don’t think I’ve ever actually replaced one of these controllers. In fact, I still have a spare controller that I’ve been carrying around for probably 15 years. I bought it the first time I encountered this problem, convinced the board had failed. Swapping in the replacement controller produced exactly the same result.
Replacing the wiring harness has repeatedly resolved this condition in the field. While performing the repair, replacing the proof-of-fire switch, high-limit switch, and vacuum switch is also recommended if their age or condition is unknown, as these components contribute to the overall circuit characteristics.
Although this is an uncommon failure, it can consume hours of unnecessary troubleshooting if the wiring harness is overlooked. I caution any stove owner or technician dealing with this issue: don’t simply assume it’s a switch.
I’ve replaced only the switch in the past, and wouldn’t you know it—the stove actually works again…or does it? A couple of days later, or even a couple of hours later, the error code comes back.
Apparently what we’re dealing with is a very small threshold that’s being crossed. Replacing a switch may be enough to get you back over that threshold, but as soon as the stove warms up, you cross right back over to the other side—the miserable side of the fence, as they say.
As of this writing, I’ve documented this failure mode on three separate Winslow PI40/PS40 service calls over the past 20 years. I’m taking the time to write this because it’s one of those problems that doesn’t come along very often, and I recently encountered it again.
If this article saves just one pellet stove from being condemned to the scrap pile because someone thought they needed a new control board, then it was worth writing.
Codes
The Lennox and IHP Winslow PI40 and PS40 pellet stoves use three Ready Light fault codes related to the safety circuit:
- 1 short blink followed by 1 long blink – Vacuum (pressure) switch fault
- 2 long blinks – High-limit overheat switch fault
- 2 short blinks – Proof-of-fire (low-limit) switch fault
At first glance these codes appear straightforward. In practice, however, they are surprisingly difficult to interpret. The difference between the long/short blink pattern and the two short blink pattern is subtle enough that many technicians and homeowners cannot reliably distinguish them during operation. Likewise, unless you’re familiar with each pattern, how does one know if two identical blinks in succession are in fact long or short? Long or short compared to what? You’re only getting one fault. As a result, troubleshooting often begins with the wrong component.
The confusion becomes even greater when each suspect switch tests perfectly. A typical service call begins with the stove displaying a fault approximately one second after the Start button is pressed. The immediate assumption is that one of the safety switches has failed.
The high-limit switch is inspected first. The manual-reset button has not tripped, the switch is closed, and continuity is present. The switch is operating normally.
Attention then turns to the vacuum switch. Applying approximately 0.10 in. W.C. of vacuum closes the contacts, continuity is present, and the diaphragm successfully holds vacuum. Again, the switch tests normally.
Finally, the proof-of-fire switch is tested and also operates exactly as expected.
At this point every component identified by the fault codes has passed testing, yet the controller continues reporting a safety circuit failure.
What Is Actually Happening?
Unlike many pellet stove control systems that simply monitor whether an individual safety switch is open or closed, the Winslow controller appears to evaluate the electrical characteristics of the entire safety circuit. It could have monitored everything with dedicated circuits, but that would have required more wires and more copper. Country Stoves, the original manufacturer of this problematic child, evidently thought they were going to sell 1,000,000+ units, and instead of having 12 wires coming off the control board, they opted for the bean-counter method of only nine wires.
The vacuum switch and proof-of-fire switch each have their own signal wire, but they share a common return conductor back to the control board. Likewise, the high-limit switch is wired in series with the auger feed motor and ultimately shares common return paths with other stove components.
To further complicate matters, after Country Stoves sold to Lennox, and later after Lennox sold the line to IHP, a hopper lid switch was introduced. This switch utilizes a resistor to simulate the presence of the auger motor in the circuit so that stove owners could open and close the hopper lid while the unit was running without triggering a shutdown fault.
As a result, the controller is evaluating more than the individual switch itself. It is effectively evaluating the entire circuit path, including:
- Wiring resistance
- Oxidized or loose terminal connections
- Heat-damaged conductors
- Aging connectors
- Switch contact resistance
Each of these conditions can increase total circuit resistance while the switches themselves continue to function normally.
This explains why a switch can pass every continuity test performed with a multimeter yet still generate a startup fault code.
Recommended Repair
If the fault is generated immediately at startup, this should be your first clue. If a fault were generated while the unit was already running, I would focus my attention on the individual switch identified by the corresponding fault code.
Your next clue is this: if all of the safety switches test correctly, but the stove consistently generates an immediate startup fault, suspect deterioration of the wiring harness before condemning the control board.
In my 25 or so years of working exclusively on pellet appliances, I don’t think I’ve ever actually replaced one of these controllers. In fact, I still have a spare controller that I’ve been carrying around for probably 15 years. I bought it the first time I encountered this problem, convinced the board had failed. Swapping in the replacement controller produced exactly the same result.
Replacing the wiring harness has repeatedly resolved this condition in the field. While performing the repair, replacing the proof-of-fire switch, high-limit switch, and vacuum switch is also recommended if their age or condition is unknown, as these components contribute to the overall circuit characteristics.
Although this is an uncommon failure, it can consume hours of unnecessary troubleshooting if the wiring harness is overlooked. I caution any stove owner or technician dealing with this issue: don’t simply assume it’s a switch.
I’ve replaced only the switch in the past, and wouldn’t you know it—the stove actually works again…or does it? A couple of days later, or even a couple of hours later, the error code comes back.
Apparently what we’re dealing with is a very small threshold that’s being crossed. Replacing a switch may be enough to get you back over that threshold, but as soon as the stove warms up, you cross right back over to the other side—the miserable side of the fence, as they say.
As of this writing, I’ve documented this failure mode on three separate Winslow PI40/PS40 service calls over the past 20 years. I’m taking the time to write this because it’s one of those problems that doesn’t come along very often, and I recently encountered it again.
If this article saves just one pellet stove from being condemned to the scrap pile because someone thought they needed a new control board, then it was worth writing.
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