Hi all,

First of all, thanks for reading my message, assuming a few people will actually read it :-)

When the temperatures started to go down in Brampton ON, I thought it would be a good idea to startup my furnace and make sure everything was working properly. Sure enough, as I flicked the ON switch on my RBI Spectrum natural gas hot water boiler (we live in an older house using a circulating hot water heating system), nothing happened, outside of the power ON green LED coming up.

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Since I do pretty much everything in the house from plumbing to electrical, building and repairs etc, I thought I would look at the inside and start troubleshooting.

Here is how far I went:
- ignition sequence doesn't start, no gas valve, no spark
- gas valve works fine, both click when I send 24V to the pilot valve and main valve manually
- There is gas coming out as I was able to light up the pilot manually
- 110V/24V relay also operated normally
- thermostat has good batteries :-)
- no other warning

So my attention started to turn toward the Honeywell Ignition unit. I took it apart and inspected it, but couldn't find any obvious problem to the naked eye. The plastic casing did show some signs of heat discoloration, but considering it's location, it wasn't really surprising. I did some research online and realized that this is a component that has a tendency to fail. So I got a (used) one off Kijiji, which as per Honeywell is the proper replacement part: the S8610U 3009.

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This is the old one, in situation.


I had high hopes at that point and replaced it the same night. Turned on the furnace, set a high temp on the thermostat and... nothing. No ignition sequence. Not even the little LED status light. After the initial disappointment, I starting searching forums and found that some people have been successful getting it to work when plugging wire connector that normally connects to #6 (24V), to connector #7 (call for heat, thermostat). Did just that, turned the furnace ON and boom, it went through the startup sequence and fire up. I thought I was in business but...

... but I soon realized that this "fix" only in fact bypasses the thermostat and was sending 24V straight to the ignition module; I was losing the ability to have my house thermostat control the furnace. It's a 2-wire thermostat BTW.

It was a good move forward however, since I now know that the ignition and gas valve both actually do work as they should.

Also, when I connect the 24V wire to the TH-W connector, the ignition module works just fine although it does return a Damper Error code. My previous module had a jumper cable molex connector on it, which you will see on the picture.

So, to summarize:
- Old unit installed: nothing happens when system turned ON and call for heat
- New unit (S8610U) installed and wired as the old one: nothing happens when system turned ON and call for heat
- - New unit installed and 24V wire (#6) connected to TH-W (#7) (wire to TH-W connector left disconnected), damper molex jump wire installed: system powers on but doesn't start (flashes a few times then shuts down)
- New unit installed and 24V wire (#6) connected to TH-W (#7) (wire to TH-W connector left disconnected), damper molex jump wire removed: system powers on but stays ON at all times (can't control with thermostat since wire is disconnected)

I also read that apparently, these S8610U units will get programmed to operate with a damper if a damper is connected to it at the first place. There is none installed in my case.

I'm out of ideas. I know most people are happy with having the system ON at all times but I need my thermostat controlling it.

I looked at the electrical diagrams and just can't figure out why the system is behaving this way.

I'm close to calling a HVAC person, although I think I'm pretty close...

I would appreciate any assistance I can get!. thanks in advance!

Mathias

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UPDATE - Oct. 13th

After 2 more hours of troubleshooting, I tracked down the problem to a defective water flow sensor. Since I completely shut down the system during the summer, it probably got stuck and opened up the circuit as a safety. The ignition module was not the culprit after all, both the old one and the new one work properly.

There is always a valid explanation.... :-)

Thanks to whoever read my request nonetheless!

Mathias