Robertshaw 780-845 Ignition Module, Intermittent Pilot, 24V

I have an old Carrier 58gsc. It would start, sometimes, then stop. Wiggling the wires seemed to help so I decided the springs connector to the lockout/ignition controller LH33WZ512A had worn out. The 6-pin connector on the old controller looked hard to replace so I took a chance and ordered this controller with friendlier looking connectors. I used $7 worth of "disconnect" terminals that came with a crimping tool and it was within my capabilities. Installation notes: I didn't seem to need to hook everything up. 'PV/MV common' and 'Transformer ground' on the new controller were left floating. I connected the sense to the adjacent terminal on the controller as suggested by the instructions. From the old connector to the new controller: Black - ground Blue - Thermostat 24V Yellow - Pilot Valve White - Main Valve Brown - No connection (This floats at 24V when the furnace is on. I think it has something to do with the old flame sensing mechanism but this controller doesn't seem to need it.) I was really pleased how quickly the furnace started up. Just a few seconds; much quicker than the old controller. Also, when I turned off the gas, the controller immediately locked out until I turned the thermostat down and back up again. Seems safe. Not sure how the flame sensing works; seems like magic; but works. At one point I connected the brown wire to PV which is wrong and the controller LED blinked then shut down which was helpful in guessing the connections. I had paid some con artist $90 to quote me $650 to replace the perfectly good control valve. This box fixed my problem for $80. Great product!

It was easy to install although I had to drill a few holes on the bracket of the furnace. Just keep track of the wires and where they go.

The Robertshaw ignition module worked great and the replacement from a Lennox SP 745 was straight forward. The wire positions are not all in the same spot so you will need to make note of this as you disconnect the old module. The ignition terminal on the Robertshaw is labeled SPARK, this is the only difference for labelling. The screws that came with kit were a bit too short so I used a more suitable length. My furnace now works great again, I am very happy with the product which saved me a lot of money in the end.

Ran into a problem with our Lennox Whisper G20 last season where it would light, run for a few minutes, then go out before getting up to temperature. Then I took a air compressor with nozzle and blew out the heating element chamber and we were fine the rest of the winter. I didn't think much of it other than when the main burner would first come on, the furnace would making a strange clicking noise. I would assume to hear a clicking noise when igniting the pilot, not when opening the main valve. This year, the clicking noise got even worse. I assume it was the sound of the MAIN VALVE relay in the ignition control. Well, eventually, the house started getting cold and in investigating, found that the furnace would light the pilot, eventually kick on the blower motor, but the main burner never came on and the system would shut down right away. I cleaned the flame sensor rod, tested the flame sensor current (1.8 microamps), but none of those things helped. I found AC voltage when the pilot lit across PV & PV/MV, but never found any voltage across MV & PV/MV. It would never open the main valve (turn on the main burner). I assume the clicking relay in the Robertshaw SP 835 (that it was currently equipped with) finally gave out and that I needed to replace the control. I ordered this on Saturday and received it Tuesday (one-day shipping? My only gripe is that I think one day shipping should mean one day) and as soon as I hooked it up, the furnace worked perfectly. Interesting difference with this model is the tail for the flame sensor which allows you to bypass it. It can be bypassed by plugging the black wire directly into the sense spade. Please don't do this- I wish it weren't equipped with this feature. Make sure the flame sensor is plugged in and the tail (the black wire) is hanging not plugged into anything. Otherwise, it will think the burner is lit, even if lighting fails, and could fill your house with gas. Anyways, so far, so good. If I have any problem with it I will update the review.

(video shows bad module before I replaced it with this new module) My 30+ year old Lennox 78UGF4-100-1 started making a loud clicking sound and wouldn't light. We called the repair man but of course it worked just fine while he was here. We basically paid $140.00 for the tech to say there are probably holes in the old wires (despite him testing wiring for continuity) and make a sales pitch for a new hvac. First if there are hole in the wires, which ones and why not replace them. Second, our previous house was built in 1959 and there weren't "holes" in the much older wiring. I initially tried cleaning the flame sensor and ignitor. The furnace fired up the 1st time but wouldn't ignite the second time. After replacing the flame sensor and the pilot assembly I had the same problem. I watched " Gas Furnace Spark Ignition Control Troubleshooting- Two Rod! " and " HVAC Service Call Bad Furnace Control Board / Spark Ignition " on Youtube and they helped me diagnose my problem. Turns out the module was sending an intermittent 12v pulse to the gas manifold (PV) instead of a steady 24v. Installing the new module was straight forward, however the order of the connections have changed from the original SP745 board. The module also doesn't have the screw mounts like the previous module. The new module comes with a 3m type foam mounting strip and two random screws. I'm not sure what the screws were for and used the mounting strip to mount in place of the old module. Hopefully it holds up. The new board also has the added benefit of a "LED Display" according to the mfr. website. It's really just a led bulb that blinks if there is a problem, but still better than nothing like the old module.