I have a garage heater with a Honeywell s8610u pilot controller. s8610u has many terminals such as MV/PV, PV, TH-W, etc all measure 24 VAC. Can I use one of them as power for my thermostat C-wire

check gas pressure before and after valve when cycling

https://heatinghelp.com/systems-help-center/thermocouple-testing-procedure/

Being as how you changed the gas valve, make sure the arrow on the bottom of the gas valve is pointed towards the burner. Check for 24 volts at the common and main valve terminals on the gas valve when the thermostat is calling for heat...terminals MV and C. You will only have 24v there if the flame sensor senses flame... either pilot flame or main gas. You coud have 24v there without gas flowing or flame if is is a thermocouple standing pilot system and the gas valve is not in the 'on' position. But standing pilot systems usually do not have flame sensors.

With a flame sensor in the system, you have to have either spark ignition or glow coil ignition. If its spark ignition check for 24 volts at the pilot valve and common terminals on the gas valve WHILE the ignitor is sparking. That would be PV and C. The ignitor should spark and 24v should be on PV and C for 30 seconds to a full minute without ignition if it is a spark-to-pilot system.

If you have a glow coil, it will energize and burn bright orange for a minimum of 30 seconds BEFORE the main valve is energized. Then MV and C is only receiving 24v for approximately 5 to 6 seconds. This gives the flame sensor the time to prove the flame....if it does not prove flame, the system shuts down.

operation -call for heat 24 volt powers up control spark starts after all safetys close pv is energized pilot valve opens and pilot flame starts and proves flame sensor after flame is sensed mv powers up opening main gas valve as call for heat satisfied 24 volts shut off

If you need further help, I’m available over the phone at https://www.6ya.com/expert/mike_9693b5ad75773352

You fried the board. Get a new one. They can't be repaired.

There are many types of modules on the market out there. If you are replacing one for a standing pilot, you will need to but a retrofit kit. On most modules, you just take the wire from the old one that is marked such as MV for gas valve, PV for pilot valve, 24v Hot, Common, Flame sensor, If it has TR for thermostat, you will use that in place of the 24 volt hot as you don't want to run 2 -24 volt connections to the module.So, you will have commons, more then one so tie them together, pv, mv, fs, tr or th, 24 V. If you can give me more info on the module you are replacing, and what you are replacing it with, I can tell you exactly how to wire it.
Sincerely, Shastalaker7

Hi!
NO you can not, as the S8910U module is for hot surface ignition and the S8610U is for intermittent pilot ignition. Sorry!

Hard to believe they sell a retrofit kit for a Gas furnace to a Customer....This is ahrd to advise you on with out seeing the schematic and if it is indeed intended for that furnace....the Spark mounting location is CRITICAL for safety so make sure that is correct above all.....OK The wire coming off the transformer and tied to the red wire going to the heat excghanger would most likely be a High Limit switch...cuts the gas off if the blower doesnt work etc or you would have a fire...so this switch must be in series with the transformer to cut power when the switch opens....the wire MV/PV coming from the "Electronic control box" needs to go to the New Gas Valve you should have which will have a termional marked MV/PV (Main valve/Pilot/valve) as your old one was for a standing pilot application and when you have electronic ignition you req a Gas valve for Intermittent pilot .....you should also have 2 more terminals on the valve MV and PV which will have seperate lines from the ignition control as well....basicvally there will be another wire coming from MV/PV going back to the transformer...make sure all wiring is correct and I would strongly advise you have a technician check your work before you attempt to use it....if wired incorrectly you could have a serious delayed ignition as its possible to power the main burner instead of the pilot if you wire it up wrong below is a typical spark wiring diagram....may not apply totally to your system but it will give you the general idea

are you sure your jumping th and th/pp? the labeling on valve is a little deceptive.should use 1st and 3rd terminal on gas valve. if your using correct terminals try same thing with thermostat wires disconnected from gas valve. this will isolate valve from all controls and safties.if it fires valve is good and need to look in thermostat loop for problems. hope this helps