HSI not Heating Up

Old 12-12-21, 08:02 PM
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HSI not Heating Up

My Rheem propane unit stopped igniting the gas during start-up due to the HSI not heating up during the HSI energize cycle. System would go through the following cycles and repeat 3 times before locking out the system.

(1) 30 second pre-purge cycle with draft inducer running
(2) 34 second HSI energize cycle, draft inducer still running
(3) 9 second propane release, draft inducer still running

Original HSI was a Norton 201N part number 62-22868-02 that measured OL for resistance. I first replaced it with a Supco IG418 which I later found out cross-references to a Norton 271N HSI and not the 201N. The Supco IG418 measured 75 ohms resistance and the furnace would then progress through the three cycles above followed by shutdown of draft inducer and startup of the circulating blower as if the propane had been ignited even though the HSI still did not heat up and no flame was produced,

I got the following measurements from hot & neutral wires at the HSI plug to ground when not connected and when connected...

I then got a Duralight HSI Part Number 62-22868-93 which is supposed to be a direct replacement for my original HSI. The resistance on this HSI measures 118.9 ohms. Same thing is happening with this HSI...furnace goes through the three cycles listed above followed by shutdown of draft inducer and startup of the circulating air blower as if the propane has been ignited, but the HSI never heats up and the propane does not ignite.

The VAC measurements from hot & neutral to ground at the HSI plug when the Duralight HSI is connected are shown below. Also shown below are the amps going through the wiring to the HSI with the Duralight plug which is only 0.19 amps during the HSI energize cycle (same as the pre-purge cycle).

I have verified that the air validation switch is closing during the pre-purge cycle and remains closed during the HSI energize cycle and propane release cycle. I also have two flame rollover switches mounted above and below my three firing tubes and I have verified they are closed during all three cycles.

The circulating blower starts with either HSI connected without any flame regardless of whether or not the flame sensor is connected to the PC board.

The Power and OK lights remain solid green throughout the cycles listed above with no blinking to indicate any type of error.

The board has a burn mark between where the HSI and draft inducer power plugs into the board and a relay. I don't know what the relay controls, but I am hearing relay clicks from somewhere on the board before/after each cycle listed above. See picture of burn mark below.

(1) Any idea what the cause would be for the HSI to not to heat up? I assume 0.19 amps is not sufficient.

(2) Any idea why the VAC readings are different for the two HSIs during the 30 second pre-purge cycle?

Old 12-13-21, 04:35 PM
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Welcome to the forums.

You need to measure 120v directly at the igniter with it plugged in and heating.
You don't care about voltage measurement at any other time.
The board knows how long to allow the igniter to heat before opening the gas valve.
With that igniter it's approx 20 seconds.

That board is no longer usable in that condition.


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