How the Rheem RGDA ignition control works

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The control is the Robertshaw HS 780 ignition control. I show how it works.
This video is part of the heating and cooling series of training videos made to accompany my websites: www.graycoolingman.com and www.grayfurnaceman.com to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages can be lethal, the fuels are highly flammable and high pressures are used. Know your limits.

Опубликовано:

27 окт 2024

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Комментарии : 35

@grayfurnaceman 11 лет назад

I have never seen the RS terminal on the Robertshaw 780 control with a terminal. I assume it is for a flame sensor. All these controls I have seen use the HSI for sensing. As for the digitizing, this is the best way I know! Maybe soon we will be able to network our brains. Thanks GFM

@ssergeant9682 4 года назад

wanted to let you know - we took your advice and found the Honeywell part for our hot water heater. the best part? it was a local person selling thru EBAY. part was new. we picked it up last night - Bill did a rough install and we now have hot water again. He (Bill) is going to mount it properly today - but he wanted to make sure it worked before the retrofit. We owe you dinner. The part was around $75 - but it's new, we picked it up same day only 30 minutes from here. the only other option was a new hot water heater which just was not in our budget. THANK YOU - THANK YOU - THANK YOU.

@grayfurnaceman 4 года назад

Glad you got it going. GFM

@ssergeant9682 4 года назад

got your reply - Bill said this: the ignitor comes on lights up the burner which heats up the tank. at some point a red light comes on - then he has to shut the power off, turn in back on - and then it will start the cycle again........it never seems to get really hot like it used to. Im terrible at being the middle man. I'm going to send a link to Bill and let him continue with questions if you don't mind?

@Guyhakverdi 11 лет назад

Dear GFM, The problem was the pilot light hood. I didn't know the pilot light hood rectifies the current but I learned. I read couple documents from Robertshaw website and remembered the rusty pilot light hood... That s all. Thanks.

@mechacc2000 11 лет назад

NL stands for local flame sensor using HSI as flame sensor NR stands for remote flame sensor using a flame sensing rod.

@grayfurnaceman 11 лет назад

From my experience, if the output from the Robertshaw control is below 24 volts nominal, the control is toast. If the gas valve shorts out, the control will shut down from low voltage. You can replace it like for like or use one of the general replacement controls from Honeywell or White Rogers. Hope this helps. GFM

@thomasjoseph5876 10 месяцев назад

Not sure if you still check these comments but I have a similar Robert Shaw ignition module but mine has the RS terminal and sensor rod. Every now and then (nothing detected to make it do this), the module won't send any volts to the gas valve UNLESS I reset it and TAP the Robert Shaw Ignition Module a couple of times. Then it will send 24 volts to the gas valve and it fires the furnace right up. I can't find any loose wires or connections at all, including the ground. I think the Module went out since I have to physically tap it to send the volts to the gas valve. The HS ignitor ALWAYS lights but of course, it ends up timing out unless I tap the module a couple of times. Anything you can think of that I am missing??? My furnace is an older Coleman Evcon low-efficiency propane furnace. Thanks

@grayfurnaceman 11 лет назад

Place one lead of your meter on the chassis of the unit and the other on the ground wire. If you read voltage, you have an open ground. Hope this helps. GFM

@grayfurnaceman 11 лет назад

Cool. Thanks for the info. I will note that on the vid. I learn something every day. GFM

@mechacc2000 11 лет назад

You should notice that there is no terminal next to the RS label. RS stands for remote sensor.

@grayfurnaceman 11 лет назад

If there is no separate flame rod going to the pilot, the spark ignitor is the flame rod. If it does not prove with the pilot flame covering the rod and the ground is good, the control has failed. Let me know how this comes out. GFM

@craigdaubbeats-rapinstrume9185 5 лет назад

I wish I could find tutorials on the RGDA 075A CR. But I can't find any. I can't even find anything on Google about my furnace. I have a little black box that burned up that's connected to a bigger metal box and can't even figure out what the damn part is.

@grayfurnaceman 5 лет назад

Try this: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ZGOVxyYCmKo.html GFM

@StevenJaimz 10 месяцев назад

Is the Honeywell S8910U3000 the module you replace the HS780 with ?

@grayfurnaceman 10 месяцев назад

That is the replacement I would use. GFM

@StevenJaimz 10 месяцев назад

@@grayfurnaceman thank you for the info. I just bought a house with a gas furnace with the old control. The furnace has not been serviced since like 1991. So now I get to service it and deal with swapping out the control

@seeittobelieveit513 11 лет назад

what is the best way to check with your multimeter to make sure you have a good ground

@philipbrown8314 6 лет назад

I wish you would tell me what part # to use to replace my door switch for this Rheem RGDA-10EA-AR the one shown in the video must be obsolete

@JustPlumDucky 11 лет назад

Voltage at gas valve is occasionally only .444vac when the HS-780 clicks to turn it on. 2nd & 3rd attempts sometimes fire it up (25vac at valve). Incoming volts to control (TH & GND) is always 26v regardless of vac (or lack of) at gas valve. Sure sign of HS-780 on the way out, or is it possible for gas valve to intermittently short out the voltage, and if it could, HS-780 would blow, and/or transformer feeding HS-780 would blow? No other ignition control on this mobile home furnace.

@grayfurnaceman 12 лет назад

No, probably because they are only ignition controls rather than integrated furnace controls. GFM

@Guyhakverdi 11 лет назад

Dear GFM, Today I went on a no heat call for a unit heater that has spark ignition with robertshaw control board. The ignitor fires up the pilot but main burner never comes on. After a minute pilot goes off too. Question does spark ignitor work as flame rod? I tried to clean with sand paper but didnt come on. so I suspected the ignition board is bad however the led is green looks like normal operation Im confused.

@ssergeant9682 4 года назад

I have another issue that I'm hoping you can advise us on. We did get the honeywell part. and it does work, but it keeps going out.......bill said a red light comes on. he's not sure what it is. then it goes out and he has to relight it.

@grayfurnaceman 4 года назад

The red light is probably the hot surface ignitor. If the burner keeps shutting down during the cycle, check to see if there is a metal cage around the ignitor. If so, replace the ignitor. GFM

@ssergeant9682 4 года назад

He's going to check into it. thanks! he said he replaced it a few years ago ago. but he didn't think it was expensive

@McCuneWindandSolar 6 лет назад

I have one of these in my furnace, and it will not send out the 24 volts out to the valve, at one time it would work for a while then stop. I would power cycle and it would work again for a few weeks or so then it go to were it was a few days then to were nothing at all any ideas.

@grayfurnaceman 6 лет назад

Replace it with a Honeywell 8600 GFM

@lPhoneBoy 8 лет назад

I would really appreciate if you could answer this question my original when out model HS780 NR308 and I happen to receive a different part from Amazon I got the HS780 34PL-308A. However it does not have the RS terminal is it safe to use? The RS terminal goes to the flame sensor that I have in my furnace its currently not connected any advice will help.

@grayfurnaceman 8 лет назад

+iPhoneDude Not thrilled with the 780 control. However, if you have a flame rod use a control that has the flame rod connection. Probably not a safety issue, but it may go out on nuisance trips. Hope this helps. GFM

@ssergeant9682 4 года назад

is there a way to trouble shoot HS780 34PL-308A - Robertshaw OEM Replacement Furnace Control Board. it's for a rheem hot water heater. we have not clue how to test it. we can order one, but if it doesn't work - they won't take it back............out water heater has been out since a power surge by comed on new years eve 2019 the theem dealers near us (60033) don't even show it because it's old.

@grayfurnaceman 4 года назад

The only troubleshoot possible is to check for 24 volts in. Restart the unit and check to see if the HSI comes on. If it doesn't, check for 24 volts to the control. No 24, check for limit or thermostat. If the HSI does come on but no gas flow, the control has probably failed. Btw, I would replace it with a Honeywell S8910U3000 control. The 780 gave a lot of problems. It is hard to fit the Honeywell control in the space, but it works far better. GFM

@ssergeant9682 4 года назад

@@grayfurnaceman I forwarded your reply to the hubby. you may get a reply from him. I'm just doing the research but don't have a clue how to do this. any suggestions on how to put the control in place of the old one? can longer wires be put on it and then surface mounted nearby? I really don't know. just throwing out ideas. thanks for your quick response.

@grayfurnaceman 4 года назад

@@ssergeant9682 I have done the replacement and it will fit inside. Its just very tight. GFM

@ssergeant9682 4 года назад

@@grayfurnaceman thanks! bill said he needs a longer fillips screwdriver, but he's got a handle on it. you're a lifesave and $$ saver. wish we could return the favor for your sharing of very useful advice