Testing a RobertShaw Millivolt Valve


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Old 01-31-24, 02:22 PM
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Testing a RobertShaw Millivolt Valve

Hi folks,

In 2020 I was here seeking help to fix my fireplace (the thread seems to have been removed). The fireplace is original to my home (1996). Back then, I replaced the pilot assembly (with thermopile and thermocouple). The fix didn't last long. The Robertshaw millivolt valve craped out. Following a trouble shooting guide I found from Regency Fireplaces, I measured the resistance between TH/TP and TP and it was infinity, indicating open. The measurement between TP and TH was 6.2.




Fast forward to today and I finally got around to purchasing a replacement valve. It is a new in the box Robertshaw 710-508. The first thing I did was to measure the resistance between the terminals as I did in 2020. Resistance between TH/TP and TP is infinity and between TP and TH, 2.1. I reached out to the seller and was provided with a replacement.. It too measures infinity between TH/TP and TP. It's interesting that both new valves are missing terminal screws.



Both new valves came in Robertshaw boxes and have the appearance of being new. What are the chances of getting two DOA gas valves in a row. I now have a small collection o doorstops.

Is there any chance these could be getting damaged in shipping or, am I just unlucky with my purchase.?
 
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Old 01-31-24, 03:17 PM
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You only have three posts...... two with adding 20A circuits and this one so nothing appears to be missing.

There are thousands of fireplace threads. None are ever deleted. The board defaults to a limited amount of threads shown based on dates. Here is a search link based on all threads
.... Page 3 of 48 pages on fireplace threads

The valves hardly ever go bad. Probably 1 in 1000.
Not sure what tests your are following but if you are checking the valve with no wires connected... as it should be... you will only measure resistance across the outer two terminals. The center terminal is a dead connection form splicing only.

This diagram shows two center terminals. They are still dead/splice terminals.
The valve is only tested on the outer two terminals.
Typically if any resistance is measured.... the valve is good.
 
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Old 02-02-24, 03:00 PM
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Thanks for the reply, Pete. Yes, I don't have that many posts as I'm fairly self sufficient at many things. And yes, there is a ton of information available. But, I've not found what I need. My original valve did go bad. The picture below shows a fried wire leading to the TH terminal. I'm not sure how that could have happened, but it would explain why the fire would go out after a short time. The wire to the magnetic coil was making contact with the terminal, but I'll bet when the valve got a big warm, the wire moved and no longer made contact with the terminal. That would trip the valve to close and shut off the gas supply.



The testing instructions are those I found online from Regency Fireplace Products. I also found something from HearthStone that has the same test, although it's for an older version of the millivolt valve. The terminals and magnetic coil are the same on both the replacement valve and the original valve.

Troubleshooting the Robert Shaw 7000 Series Gas Valve

The diagram you posted does not match what is on my valve. The picture below shows the terminals.


TH/TP, the left most terminal looks to be a dead connection for splicing as you commented.


This is how my setup was wired.

With all new parts, this should get me though until I take my dirt nap.
 
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Old 02-02-24, 03:53 PM
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That does not follow most valves.
Typically the center terminal is the splice point.

In any case...your splice point (Th/Tp) is on the left.
The coil is on the right two terminals.... Th and Tp.

The wire in that valve is not burned.
There is not enough current thru the valve to cause anything to burn.
More than likely that wire was burned when soldered.

Loose coil wires on furnace valve terminals is more common.

The two blue circles illustrate the solder coil connections.

 
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Old 02-04-24, 09:09 AM
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It looks like I'm good to go!


The pilot light looks really good.



It fires right up and I'm getting a wee bit over 500mV
 
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Old 02-04-24, 08:08 PM
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Awesome job.
 
 

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