Installed new gas valve, pilot stays lit valve does not open
I just replaced my wall furnace gas valve with a Robertshaw 710-205. The pilot lights and stays lit, but the main valve does not open to ignite the burner. Any advice?
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Is the knob set to on vs pilot? Is the pressure within the range of the valve?
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Yes to both. Gas cock was turned to on. And the pressure is within range, 11w.c. and there's a new l.p. regulator on the valve.
Since the pilot is staying lit, is it reasonable to say the thermocouple is operating correctly?
The only other thing that may cause an issue is the on valve pressure regulator. I emailed Robertshaw and they said I did need the on valve regulator to convert to lp, even though I already have a regulator at the source. The source regulator brings the pressure to 11wc going into the valve. The on valve regulator seems to do the same thing. Any thoughts? Could they be conflicting?
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Yeah, the thermocouple just holds the safety valve in. At least I think it is total shutoff. try turning it off, letting it sit a minute, the light the pilot and don't hold it and see if the pilot goes out. if the pilot goes out if you release it immediately then the thermocouple is good.
The main valve is operated by the fluid in the cap tube and bulb.
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There is an inline regulator before the furnace set to 11" wc? The gas valve was NOT converted to LP? Of course it needs the LP conversion kit. And manifold pressure should be set to whatever the furnace manufacturer recommends. Usually 10".
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there is another thread on this. this is in an rv and the valve i think does not have an integral regulator.
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It DOES have an integral regulator(I installed the l.p. conversion kit as the valve is sent as natural gas) and also a two stage regulator at the l.p. source that liwers pressure to 11w.c.. This is a brand new valve installed today.
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@HVACNUT Yes there is a regulator before the furnace that is set to 11w.c. and I did convert this valve to l.p. with the converter kit/regulator. My question is...does it need both? Because there is a 'cover' to replace the integral regulator for unregulated use, which is actually already set at 11wc. at the source. I was wondering if 2 regulators would cause an issue. When I ordered it I thought the redundancy would be useful.
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My bad, I apologize. I thought I had included more info in the original post.
This is a new valve with an lp conversion regulator installed.
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regulators can only reduce pressure. if the incoming pressure is 11" wc and you have an11" wc regulator in the valve, the regulator in the valve is probably going to lock out because it can't maintain pressure.
did you ever figure out what the manifold pressure of the appliance is supposed to be?
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@Maddogandnoriko , ALL LP gas lines have a regulator at the tank, and, or at the penetration to the building. Typically, that pressure is 11 to 13 inches wc Hg. A typical atmospheric LP furnace asks for 10 inches wc manifold pressure. The conversion kit for the gas valve must be used to "regulate" that 11 to 13 inches down to 10 inches. Or whatever pressure the manufacture specified. You can't achieve that with the Natural Gas spring.
But at the moment, none of that even matters because the gas valve is not opening, correct? You said it's a wall furnace. 24 volt or milivolt? What make and model furnace? How old is it? Can you post a pic of the wiring diagram?
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hydraulic. see this post:
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@HVACNUT It is a standing pilot model with a copper bulb style 'thermostat', no power, 56 years old. All parts look good, burner is cast iron and in solid shape. Enamel in the box is almost all intact.
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Do you feel/hear anything when you turn the temperature knob up & down? That should be the opening point. If you hear that but gas doesn't come out, it's decent proof the valve is defective. It might be worth putting the remote bulb in cold or ice water to see if that'll make it open.
It's possible that whatever fluid it used leaked out.
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Do you have a meter to check millivolts? If not, replace the thermopile and cross your fingers. We don’t have a diagram to see if there's any safeties in the circuit. It's the voltage from the thermopile that opens the gas valve. It doesn't need much voltage to keep the pilot lit, but it does to open the gas valve. If the pilot flame is nice and blue and steady and completely surrounding the upper portion of the thermopile, then replace the thermopile.
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it is hydraulic, not millivolt. there is just a thermocouple to hold the safety valve open. the main valve is operated by a capillary tube and bulb.
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So, IOW, time to upgrade.
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@HVACNUT Why upgrade? I keep hearing this. Upgrade and use battery power and extra components for a 15' trailer?
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@mattmia2 I think I have the original installation manual and will see if it has the manifold pressure.
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at the very least get a low level CO Detector
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I have a manometer and an air compressor and am going to check if the valve is opening and the orifice could be clogged. Could be that easy. Probably not.
My guess is it is one of three things, clogged orifice, faulty valve, or the two regulators are conflicting.
Does anyone have a definitive answer if I really need an on-valve/integrated regulator/converter if the gas is already regulated to 11w.c.?
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what are you doing with the air compressor?
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you need somethin more like a respirator bag. be careful, once the residual gas hits a pilot or ignitor things can get exciting for a moment.
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@mattmia2 The install manual says 10½ - 11w.c., but it is a bit vague if that is input or output.
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@mattmia2 blowing out the orifice with the compressor.
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Respirator bag?
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@pecmsg Done deal. For what it's worth, part of why I am trying to save this furnace is it vents all(most?) of the combustion outside thereby minimizing CO2 ans wator vapor in the cabin. We also got a propane detector also.
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almost All???
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@pecmsg yep, the experts are putting catalytic heaters or Mr. Buddy heaters in the rebuilds that vent zero combustion out, Crack a window, That's Camping World, so yeah, its supposed to vent it all, does it? I dont know...exactly. Before the valve crapped out the CO2 detector and the propane detector never went off.
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if you want to chance it that’s up to you.
NOT ME!0 -
@mattmia2 I thought about respirator bag...to flush excess gas after testing? I'm not in a huge hurry, so have been waiting a healthy 30 min or so before trying anything with fire.
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Okay...put the manometer on the valve. It is definitely opening, but only 9w.c. I don't really have a sense of inches of water column, but assume it's enough of a difference to not light the burner and gas is accumulating in the burner body.
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The real answer here is.....there is a 1" pressure drop across the valve.
Thanks....
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From what I am reading here, somehow you have been able to get 9" WC on the outlet side of the gas valve. This should give you some gas in the main burner to be ignited by the pilot lite. I have a feeling that the burner outlets are not properly lining up with the pilot flame. In a case like this there is often a large puff with a lot of flame rollout when the main flame eventually lights. Are the main burner openings near the pilot flame getting any gas flow? Are the main burner openings accessible that you can use a log lighter or long match to get the main burner to light when the main valve opens?
Once you actually see the main burner flame, you may find that the openings near the pilot are clogged and thatis why the main burner is not lighting. The pilot flame is too far away from the main gas.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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It is a modulating valve, right? so the outlet pressure will vary depending on how close it is to the setpoint.
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The center knob simply actuates the main operator in reaction to temp. changes sensed by the hydraulic bulb. However, the manifold pressure being released by the operator head is controlled by the little fixed pressure regulator on the right side of the valve. When doing the LP conversion, there should have been an orange circular rubber gasket with 4 holes- 12,3,6, and 9 O'clock positions. On the operator head casting, there is a circular area defined for this gasket to fit. There are two studs or nubs- 3&9 O'clock positions. You must hang the gasket correctly on these studs before attaching the regulator body. The easiest way to keep the gasket from shifting is to lick it then stick it. A major mfr has taught this method since 1994 I'm aware of with no problems plus I discussed this expressly with the Robertshaw reps at a national trade show and they confirmed to do it that way. If it shifts, you'll leak gas but it won't flow into the mixer tube to the orifice. There is a 1/8" NPT screw plug on the outlet end . Take a 3/16" Allen wrench, replace it with a brass barbed hose fitting to measure manifold pressure. On a call for heat, if no gas existing valve, replace the valve if you're sure its calling. Apply cold to the bulb with it turned up fully. If it does open but the manifod pressure is not to spec. (usually 10 wci on LP but PMI), you can remove the dummy cap on the regulator, adjust it to spec, replace the cap. If you're certain gas is existing the valve then disconnect your mixer tube, remove the orifice and blow it out. You may simply have a spider web blocking the flow of gas on an otherwise fine valve. Never blow pressure into either end of the gas control valve.
Now, how old is this dinosaur? If its as old as it seems, you should be more worried about a rotted out heat exchanger, high CO, bad venting, etc. Forget CO2- get a low level CO monitor. You're exhaling CO2 btw. Regardless, if you get it to fire you'll need to run combustion analysis to verify proper operation and tune it. If not a pro, hire one.
HTH
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