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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8258
Experience:  Furnace, A/C and heat pump specialist.
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Here, I have a fireplace with a Robertshaw DS845 controller.

Customer Question

Customer: Rich here, I have a fireplace with a Robertshaw DS845 controller. The fireplace is controlled by a wall switch. Activating the switch, the fireplace ignites and after a minute or so the red LED on the 845 starts to flash, (false flame failure indication?) but the fireplace flames do not go out even when the wall switch is turned off. If I access the 120V power cord to the 24V power supply and unplug it, the fireplace continues to burn. Do I have a faulty gas valve?
JA: Thanks. Can you give me any more details about your issue?
Customer: If I turn off the gas valve, the flames go out (obviously) and after a minute or so, I hear the gas valve click. I assume it is closing. If I only turn off the wall switch, the flames will continue for about a minute or so and then go out, again when hearing a click from the gas valve.
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Customer: yes
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Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
If it helps, the fireplace is a Heatilator, model GBST36E NAT, serial no. GA931053
Expert:  airheatman replied 1 year ago.

It sounds like you have a faulty control module. If burners are lit and you get a faulty flame error, the module has failed.Also if the module does indeed sense there is flame present when it should not be,it should immediately cut power to the valve to shut it down.

Customer: replied 1 year ago.
I understand that when the module fails, power to the valve should drop and the valve should close. That is what was expected when primary power to the control unit was disconnected. Under those circumstances, why did the gas valve remain open?
Expert:  airheatman replied 1 year ago.

Can you verify with a meter that we do indeed lose signal to valve? If we know we are losing power to valve then yes, sounds like valve may be sticking, but module definitely has an issue if it says we have a false flame when the burners are on and thermostat is calling for them.Now if we only get the false flame error before or after we should have flame , issue can be valve sticking.

Customer: replied 1 year ago.
I have not metered the valve and I will do that to verify. Thing is, when power is dropped to the control module, the LED goes out, I assume that means no more 24VAC being supplied to it and therefore no 24VAC can go to the valve. Loss of power to the valve, I assume again would create a fail safe closed condition. Am I missing something?
Customer: replied 1 year ago.
The other troubling thing is that the false flame present error happens when the flame is actually present.
Expert:  airheatman replied 1 year ago.

Yeah that error when flame is on and should be is what leads me to suspect with the module.

Also looking at the wiring diagram it appears this gas valve operates on only 3 volts rather than 24 volts.

Expert:  airheatman replied 1 year ago.

Also valve says 3v

Customer: replied 1 year ago.
Interesting, I just did some metering and voltages are as expected. 26VAC actual present at the valve with flame present. With flame not present, 0 volts at valve but valve is still open. I tapped on the valve body very lightly and it closed immediately. The tap was so light that I am not sure the valve closure was a co-incidence. I want to repeat the failure but now am unable to do so. The thing is operating normally. I will let things thing cool down for a while before retrying and keep you posted. Also the valve you show is different from the one I have which is Heatilator pn.srv462-500b made by Maxitrol. It is starting to look like multiple failures, the false 'flame present' error and valve not closing condition.
Expert:  airheatman replied 1 year ago.

I understand,Manufactures are often making change sand not unusual for manuals I have to be a bit different.I agree that you may have more than one issue.

1.Valve should close when voltage removed.

2.We should not get false flame when thermostat is calling for heat and we have flame.

Customer: replied 1 year ago.
Do you know of a way to diagnose the flame present sensor?
Expert:  airheatman replied 1 year ago.

The only test I am familiar with is checking to verify flame sensor is procuring enough micro amps to tell control that it is ok to stay on. But that would only be beneficial if we were getting an error saying flame NOT sensed.

Customer: replied 1 year ago.
>But that would only be beneficial if we were getting an error saying flame NOT sensed.
Maybe I am not doing a good job describing what is happening. What is happening is the red LED on the control unit begins flashing while the burner is operating normally, flame present. It is my understanding that the flashing LED is a flame NOT present indicator. Am I mistaken?
Expert:  airheatman replied 1 year ago.

My manual does not have an error code explanation.Do you see the error code chart on unit?If so tell me exactly what it says for flashing LEd means

Customer: replied 1 year ago.
I saw it in a previous post on justanswer.com. Havent been able to find and info about that anywhere else on the net.
Expert:  airheatman replied 1 year ago.

I can open to other experts and see if they have more info. My understanding in the beginning was that you knew it was sensing false flame while running.

Customer: replied 1 year ago.
Thanks, ***** ***** the confusion.
Expert:  airheatman replied 1 year ago.

I am going to open to other experts to see if they have more concrete ideas.I could throw out a guess and say replace board or valve or both, but would be very unprofessional.Lets see if others have ideas.

I have opted out of the question to see if perhaps other experts may have more information and can assist.Please do not rate or reply as that will send question back to my desk and delay getting assistance..Please stand by to see if another expert can assist further.