Resideo S8910U3000 Universal Hot Surface Ign Mod

My furnace had a bad Robershaw HS780 34NL-306A. We bought our house 4 years ago and last week our older Coleman gas furnace stopped working. I've never worked on a furnace before so I taught myself about furnace operation, safety, and troubleshooting (I enjoy fixing stuff). After leaning what a hot surface ignitor is, I thought that must be the problem. It did heat up and glow orange but the gas did not ignite. These go bad after a few years and either don't heat up or stop sensing flame. I also tested if 24V was getting to the gas valve after the ignitor heats up and there was no 24V (tested with both a clamp-on ampmeter and a/c voltmeter), so I knew the control board was confirmed bad and I figured I'll replace the HSI since it was at least 4 years old, maybe much older. I replaced with this Honeywell + new ignitor for a total cost of $148 + $19.98 and now the furnace works great again! Before fixing this myself, I called the local HVAC company and told them my furnace stopped working and I suspected the control board might need replacing because it's not sending 24V to the gas valve, and how much they would charge to replace the board and the hot surface ignitor. They quoted about $1100. I think this was for a workday call and not the weekend/night rate. I suppose they have a lot of overhead they need to cover and the San Francisco Bay Area is an expensive place so I'm not totally surprised at the quote. Be sure to test the new flame safety board by doing the following:: 1) While the furnace is running, turn off the gas going into the furnace. This will kill the burner flames and the HSI will no longer sense the flames and should shut down the gas valve (you should hear the gas valve solenoid click closing the gas valve shut). 2) Test gas leaks with soapy water on anything that you moved. Actually just check every gas connection and your gas water heater while your at it. Also I'd like to mention the 306A in the Robershaw model # means try 3 times to ignite and test 6 seconds for flame sense. Other models end in 304 (4 seconds), 106 (1 try and 6 seconds), etc. Just set the dip switch on the Honeywell to 1 or 3 tries and 4 or 7 seconds. 7 seconds in within the 6 second Robershaw spec according to the excellent documentation provided.

This was a great replacement for my 30-year old control board. Installed in a few minutes, connected the wires and the furnace functions like new.

Price is what it is bottom line the product works. Fixed our furnace. Not recommending anyone fix their own furnace. It is easy to install though.

Just installed as a drop in replacement for a Robertshaw HS780 34NL-306A in an older Coleman furnace. I only had to replace one connector on one wire. This unit replaces many other models too. The manual actually explains the HS780 model numbers (34 seconds ignition warm up, Natural gas, Local flame detection - uses the ignitor not a separate rod, 3 retries, 6 second flame detect) - see the PDF of the Honeywell manual for more details and other models. I would have been happy buying a replacement Robertshaw but their model numbers are confusing and hard to find information on and sellers seem vary on clarity on which HS780 you are getting. This replacement is working great, gives you a diagnostic LED and replaces many models. Update: May 2018. Ran with this all winter without issue, so appears to be reliable too.

If you're qualified to do your own work, it makes sense to have one on hand. Easily wired and programmable for a number of different applications. And the price is less than the minimum cost of a house all. By having one on hand I've been able to have my furnace back on line in less than 1.5hrs. (it was -25f on a Friday night. An emergency call would have run $500+) Pretty cheap insurance for an older furnace or water heater.

Good product

Works as advertised

needed a new ignition sequence controller for failed older unit. easy straightforward to install and saved $600 plus installation and trip fee

Seems to be what we need.