Any gas valve experts out there?!

[rwh63]

hi,

i am the original owner/user of a 1996 Vermont Castings Radiance B-vent propane heater. the original valve assembly lasted quite a long time, then it started to get "sticky", so that it wouldn't respond to the millivolt signal to start up. since the failure of that original valve, i've had the same thing happen to its replacements (i think i'm on my third replacement).

the method to get it running has always to tap the underside of the valve while the thermostat is on. then it whooshes. not knowing the internals, it seems a valve is stuck. oddly, it responds immediately to shutting down, and will fire right back on if it is hot. cold start, no.

anyone know what is happening internally, and is replacement the only solution? btw, it has always been a Robert Shaw valve.

 

[coaly]

Have you taken a volt meter reading to see what the voltage from pilot generator is? During a cold start, there is less voltage generated. This electric flow energizes a electro magnet that opens valve. Could have almost enough power to move the steel rod/plunger to open valve, and a vibration from tapping helps it pull to magnet.

A simple test is after lighting pilot, wait a few minutes to make sure generator is hot enough if weak. You can add more heat to it with a lighter or small torch to see if that makes the valve open by adding more heat to increase voltage.

When hot, the generator will have more voltage, opening valve easier. (making a stronger magnet in valve) Does this have an external thermostat, or using one attached to appliance? Wire gauge reduces voltage since this is low DC voltage. Jumping the terminals at valve has less resistance than a run to thermostat, so if this opens valve easily, low voltage from longer runs is the issue. A voltage reading with thermostat off will show no load from generator to main burner electromagnet coil. Turning on will show voltage drop while on. Compare these to specifications of generator.

Not normal for valves to fail. It is normally the power supplied to it. Confirm you have proper voltage and all connections from generator are clean. If wires, clean and WD-40 wire ends to prevent corrosion. If coax, remove and polish the positive conductor end that seats in valve. The valve itself is the last to expect.

If you have lower voltage for any reason, a new valve that opens easier can be masking the problem. The new valve works until it requires a little more voltage to open.

 

[rwh63]

hi

thx for the response. not sure what the pilot generator is. this stove has a running pilot, so always on. the external wall thermostat is wire-type. length of wire is about 12 feet. wire is original from 1996. valve assembly works fine for a period of time after installed, then predictably fades, esp. from a cold start. shuts off fine after a quick cold start, but doesn't want to open.

i see you use the term "generator"; what are you referring to?

 

[coaly]

The part next to the pilot that the pilot flame heats is a generator. When it is smaller, it is called a thermocouple when it only powers the pilot safety on units that don’t have a thermostat. (They produce 30 Millivolts -MV or 1/3 of a volt) When you have a thermostat, the generator is much larger called a thermopile. (They produce 750 Millivolts or 3/4 volt)

When hot, tiny dissimilar metal rods bend inside making contact with case. This causes electrolysis which is a minute electric current flow. When lighting pilot, you are pressing a knob that actually pushes a steel rod like a nail against a electromagnet head. When pressing in, this opens the safety allowing gas to flow into valve. While holding knob in, you are manually holding safety open for pilot to light. As the generator heats up and starts generating current, this power goes to a winding in the gas valve that becomes a magnet when power is going through it. When pilot heats generator enough, you can let go, and electromagnet holds safety valve open for you. In the event of pilot outage, generator cools, stops generating current, and valve is spring loaded closed to shut off gas flow to entire valve.

In your case, this current from a larger Thermopile is also used to go to the points in thermostat. The wire gauge is critical since you have voltage loss due to wire length to thermostat, through points ( very low resistance in the correct low voltage thermostat since the thermopile generates about 3/4 volt. Under a volt is considered millivolt, hence the name millivolt control) This voltage from thermopile starts out at 750 MV or 3/4 of a volt. It must go from one wire on thermopile generator through wire to thermostat, across points when closed, back the wire to gas valve to energize the electro magnet to open main valve to allow flow through burner. That is how it works.

Parts in valve do not normally fail. You probably have low voltage making it back to the valve to energize the magnet. Not fixing the issue, you are masking the problem with a new valve that opens easily until a little more current is required to open it. You need to check the electric system with a volt meter to diagnose the problem.

The most common issue is a dirty or weak pilot flame not heating the generator enough to generate the needed voltage. ALWAYS clean pilot first and check voltage to make sure it is generating enough.

The thermopile gets weak over time and is the next most common part that fails. Any electric diagnostics starts with the supply. Make sure it is generating 750 MV with a volt meter, Thermopile wires disconnected, no load. Hold pilot knob down to remain lit while checking voltage output from generator.

If you have proper voltage, check resistance in the rest of system.

First remove thermostat cover and clean points. Remove the rough striker on a match book. Fold it in half so the rough side is facing outward on both sides. Open points by turning thermostat towards hotter setting. Put striker material between points, lower thermostat so points close on paper striker. Move back and forth to polish points.

Make sure ALL wire connections at thermostat and gas valve are clean, bright and tight. The wire used is commonly thermostat wire or thin gauge bell wire. Many times this is not heavy enough and causes voltage drop. There is no such thing as being too heavy. Low voltage DC has a lot of voltage drop per foot. So jumping the thermostat terminals on valve takes the thermostat and wiring out of the equation. Jump the wires on gas valve to see if it lights burner every time. When it won’t light, jump the terminals marked thermostat together on valve. This is doing the same thing the thermostat does without the resistance from wiring or thermostat.

The problem has been since it has been installed. Verify a millivolt thermostat is used, and correct wire gauge was used to thermostat to prevent voltage drop.

 

[rwh63]

generator: thx for clarifying the term. i have replaced it, maybe once, don't recall. i never do any maintenance on it. you are saying that perhaps it gets an exterior coating on it that should be removed (like cleaning a battery terminal)?

pilot: pilot flame is strong. it never is put out during the heating season. i have never done any cleaning to it, never seeing a reason to.

valve: i was always assuming that there was moisture from the gas slowly corroding the interior, causing the internal action to get sticky.

checking generator: you are suggesting shutting down the pilot, disconnecting its wires, and testing with a multimeter?

thermostat wire: it is standard thermostat wire. are you suggesting changing that?

pics of valve and stove interior:

 

[rwh63]

ok, nothing definitive, but i decided to take off the thermo wire and hook up the on/off switch. btw, the red wire bare end broke off during unscrewing (those wires are very thin). hooked up the toggle. relit the pilot, waited a while, threw the switch. nothing, back and forth a coulee times, then left it on. hadn't used the switch in forever. after about 2 minutes, it went on. gonna run it that way for a while, and prep two new thermo wire ends.

 

[rwh63]

update: let it run for about 15 minutes. shut it off via switch. gave it a minute, switched back on, nothing. let it sit for about two minutes, nothing. rocked the switch back and forth, nothing.

 

[coaly]

Pilot burners need to be cleaned because there is a air intake just like on the main burner that indoor air with dust and contaminates goes through to mix with the gas. If you have indoor animals, it should be routine to clean seasonally. Same as main burner. You won’t notice the pilot flame decrease in size over time. It is more noticeable when the air intake gets partially clogged with dust. The pilot flame goes from all blue to having a yellow tip. The BTU of pilot burner has to be enough to heat the thermopile to the correct temperature to generate the correct voltage. I assume the pilot flame in picture is correct for the portion of flame that lights the main burner. It is not yellow. Can’t tell in the pic if this pilot is the type that also burns with a full ring of blue around the entire thermopile. Older pilot models were like that. Some have flame tray only cuts across the upper 1/3 of the thermopile, others have little slots with small flame all the way around it. Depends on pilot burner style and type. You would see little slots all around the base of thermopile for gas to come out, if that is the type. There is no visible flame around base if it is that type.

The white deposits that may form on the thermopile / generator is from dust and contaminates in the air going through the pilot burner. Only if excessive would they reduce the heat to the generator. They can be cleaned off with scotch bright or small wire brush. It should come off like a powder.

The red and white wires in the silver shielded cable comes from thermopile. They need to be very clean, as well as screws on valve. I always spray with WD-40 to clean and that puts a protective coating on them from oxygen and moisture in the air to prevent corrosion and poor contact. Same as thermostat wires on valve and at thermostat. Each connection is a little loss resulting in a total dropping voltage by the time it makes the loop to thermostat and back. This is a very low voltage and you need almost all the voltage thermopile generates to open the valve.

Moisture in propane vapor; (providing this is LP and not Natural Gas)

Any moisture in the cylinder or tank will stay at the bottom. Water is heavier than petroleum products. Propane boils at extremely cold temperatures well below zero. Since the fluid in tank is always above its boiling point, it boils in the tank and only the fuel vapor exits. Any water at the bottom is not turning to vapor since it is not above its boiling point like the liquid propane. If there is any moisture escaping, it can freeze at the needle orifice in the regulator outside. This is when extra methanol is injected into fuel. There should be a drip leg on the supply line at gas valve to prevent any contaminates from entering valve. There should be no contaminating fluid in the fuel anyway to prevent cylinder or tank damage. There is methanol added to propane that boils off any water in the fuel like dry gas added to gasoline in the winter. You can get an oil residue from the odorant in the line, but this fluid would drop into the drip leg before entering valve. The drip leg is required by code.
There are many old millivolt gas valves from the 50’s still in service. In the 25 years I serviced this equipment, I may have replaced 3 or 4. And that was probably from abuse, floods, or leak around control knob when pressed in. Newer 12 or 25 volt valves with double windings and double shut off is another story. These old ones just work.

To test generator, remove red and white wires. The red is normally positive. Light pilot and hold safety knob in to keep pilot lit. Read voltage between red and white wires. That is full generated voltage with no load. When connected to valve, test voltage with pilot only lit. You will notice a slightly lower voltage. This is due to power going through the electromagnet winding for the safety valve to keep fuel open into gas valve. Then turn on thermostat and watch power drop since voltage is now also going through the main burner valve electromagnet windings. When voltage is low it may not open valve immediately. When the thermostat is turned on high resistance in the circuit can cause a delay until voltage builds up enough to pull the steel rod into the magnet coil to open valve. That is when you tap on it and this may help it open. You aren’t loosening anything in valve, you are vibrating the valve and the weak power making the magnet not as strong as it should be helps it open. (Like an old stuck solenoid on a starter that a good tap makes it work) Inside the valve is the electromagnet with coil winding also called a solenoid. Same principal, only with millivoltage.

If a electromagnet winding is shorted it will drop current to zero and safety will shut off without the power to hold the safety valve open. That is a shorted failure. When winding is open, no power travels through winding and there is no magnetic force to open valve, so valve fails in closed position. You can test winding with an ohm meter. It should read resistance through winding. Not zero, shorted; Not infinity, open.

Notice how a gas man has to be well versed in electrical circuits. Most troubleshooting is actually electrical, not always pipes, tubing, pressure and gas flow.

Next time this fails, put a jumper wire from the white wire terminal to the outer red wire. These are the thermostat wires. If it lights main burner, it is not a gas valve problem, it is low voltage losing voltage in the thermostat loop. When you take jumper off, don’t be surprised if the burner stays on. You just gave it a surge of current to open valve, and it has enough through thermostat loop to keep valve open.
(Notice the TP marking on valve is the center terminal for Thermo Pile (this powers safety valve winding) and the two outer terminals are marked TH for THermostat going to the main burner winding)

 

[coaly]

update: let it run for about 15 minutes. shut it off via switch. gave it a minute, switched back on, nothing. let it sit for about two minutes, nothing. rocked the switch back and forth, nothing.

Could be corroded contacts in the manual switch. Jump thermostat terminals (outer terminals) on valve and burner should come on. (You can do this with paper clip or short wire)

 

[coaly]

ok, nothing definitive, but i decided to take off the thermo wire and hook up the on/off switch. btw, the red wire bare end broke off during unscrewing (those wires are very thin). hooked up the toggle. relit the pilot, waited a while, threw the switch. nothing, back and forth a coulee times, then left it on. hadn't used the switch in forever. after about 2 minutes, it went on. gonna run it that way for a while, and prep two new thermo wire ends.

That is thermostat wire, sometimes called bell wire. It very well may be too thin for the current flow needed for the low voltage. Realize the run is double. From red side you have the run length to thermostat, loss at thermostat connection, loss through points, loss through white connection on thermostat and then the loss from footage all the way back. All these should have been done with heavier gauge wire to alleviate a lot of problems I’ve corrected. Connections love WD-40! Again, make sure this thermostat is rated for millivolt use. Higher voltage thermostats for 12 volt won’t work properly.

 

[coaly]

Definitely has marginal power when it takes a couple minutes to come on. Won’t say it’s not common, but when right it should open and close the valve with a definite click immediately every time. I would confirm the pilot is strong enough first. Everything can be ok in the electric system and simply not enough BTU from pilot. I always clean first before getting involved troubleshooting a problem that may not exist. Always start at the source. In this case the power generation to confirm proper voltage. If you get 500 MV and it slowly creeps up, probably not enough BTU to bend the dissimilar metals together tight enough to generate enough voltage.

Been 14 years working in the field with these, and just realized I really don’t miss it!

 

[rwh63]

That is thermostat wire, sometimes called bell wire. It very well may be too thin for the current flow needed for the low voltage. Realize the run is double. From red side you have the run length to thermostat, loss at thermostat connection, loss through points, loss through white connection on thermostat and then the loss from footage all the way back. All these should have been done with heavier gauge wire to alleviate a lot of problems I’ve corrected. Connections love WD-40! Again, make sure this thermostat is rated for millivolt use. Higher voltage thermostats for 12 volt won’t work properly.

It’s a mercury dial style. I have electrical contact cleaners, like Deoxit.

 

[rwh63]

btw, what gauge wire do you recommend that will fit into the thermostat retainers? current wire casing reads 24-2 type CL2.

 

[coaly]

It’s a mercury dial style. I have electrical contact cleaners, like Deoxit.

I mentioned to make sure the thermostat was millivolt capable. There is no Honeywell mercury thermostat for millivolt systems, I don’t know of any others. It must say millivolt or millivolt capable somewhere on it. It is probably a low voltage thermostat. (12-24 volt) A high voltage thermostat is 220 for electric resistance heat.

See if it has a heat anticipator in it.

Removing cover, this will be a variable resistance wire with a adjustment to set, like a pointer that sets to different numbers. If so, this is not a millivolt thermostat and has too much resistance for that system.

A anticipator is a small heater in a thermostat for low voltage systems using a transformer on gas and oil burners. The power going to that type thermostat goes through the resistance wire or coil and heats the area inside thermostat cover. This makes it warmer next to bimetallic spring so the burner shuts off prematurely before temp is up to set temp in house. This anticipates the blower or circulator to remove more heat from furnace before blower shuts off to prevent overshooting set temp. If it has a heat coil in thermostat, the millivoltage has to go through this resistance as well. It won’t work properly.

 

[coaly]

btw, what gauge wire do you recommend that will fit into the thermostat retainers? current wire casing reads 24-2 type CL2.

18 gauge up to 40 feet. 20 feet one way makes 20 feet back. 16 gauge to 64 feet. 14 gauge to 100 feet.

The -2 means 2 wires in casing. Wires wrap around screws on millivolt thermostats accepting these sizes.

No such thing as too heavy. It just costs more.

 

[rwh63]

Quick pics:

 

[rwh63]

did some quick searching. will look at millivolt specific thermostats. i have used digital/programmable thermostats in the past. i like the simple non-battery nature of the mercury thermo. no batteries, no programming, everyone understands it. maybe a nest brand?

 

[coaly]

did some quick searching. will look at millivolt specific thermostats. i have used digital/programmable thermostats in the past. i like the simple non-battery nature of the mercury thermo. no batteries, no programming, everyone understands it. maybe a nest brand?

That is fine for your system with no anticipator. Powerpile is synonymous with Thermopile. (literally multiple thermocouples inside to increase voltage) Notice the long slot on the left is missing the resistance wire. They use the same base for both. Still remove wires from it and put them together to make sure burner comes on every time they touch. Make sure wire ends are clean and bright. If it doesn't, jump thermostat wires at gas valve. (the two outer screw terminals) If this brings it on every time, replace thermostat wire.

 

[rwh63]

so, the mercury thermo is OK? i dug up a millivolt honeywell digital i had tried in the past. seemed better than the mercury, but still delays on start up (again, quick to shut off).

you're suggesting taking the two wire ends from the thermo and touching them. that manually jumps the valve. or, take those ends and touch them to their respective colored wire to also manually jump. does it shut off after separating the wires?

 

[coaly]

Yes, the valve is spring closed when wires are apart. Connecting the two outer terminals puts power to the electromagnet opening valve. Putting them together does the same thing as the thermostat connecting them together. The thermostat is simply a temperature operated switch.

At thermostat you have the resistance added of the length of wires. At valve there is less resistance, so if it works immediately at valve that shows resistance slowing it down in the wires. That thermostat for this system is fine.

24 gauge is not heavy enough for this run.

 

[rwh63]

i tried the jump start from the thermo end. worked, kind of. seemed to still be delays on the start up. local hardware has thermo wire in 18-2 and 18-3 gauge. probably should upgrade that anyway, see if it will make the difference. and, thx for all of your assistance.

 

[rwh63]

upgraded to 16 ft of 18 gauge thermo wire. can't yet say if it works better doing a jump, but my digital thermometers don't seem to do well with it. maybe i need to pick up a thermo more dedicated to pilot driven generator.

Pilot burners need to be cleaned because there is a air intake just like on the main burner that indoor air with dust and contaminates goes through to mix with the gas. If you have indoor animals, it should be routine to clean seasonally. Same as main burner. You won’t notice the pilot flame decrease in size over time. It is more noticeable when the air intake gets partially clogged with dust. The pilot flame goes from all blue to having a yellow tip. The BTU of pilot burner has to be enough to heat the thermopile to the correct temperature to generate the correct voltage. I assume the pilot flame in picture is correct for the portion of flame that lights the main burner. It is not yellow. Can’t tell in the pic if this pilot is the type that also burns with a full ring of blue around the entire thermopile. Older pilot models were like that. Some have flame tray only cuts across the upper 1/3 of the thermopile, others have little slots with small flame all the way around it. Depends on pilot burner style and type. You would see little slots all around the base of thermopile for gas to come out, if that is the type. There is no visible flame around base if it is that type.

The white deposits that may form on the thermopile / generator is from dust and contaminates in the air going through the pilot burner. Only if excessive would they reduce the heat to the generator. They can be cleaned off with scotch bright or small wire brush. It should come off like a powder.

The red and white wires in the silver shielded cable comes from thermopile. They need to be very clean, as well as screws on valve. I always spray with WD-40 to clean and that puts a protective coating on them from oxygen and moisture in the air to prevent corrosion and poor contact. Same as thermostat wires on valve and at thermostat. Each connection is a little loss resulting in a total dropping voltage by the time it makes the loop to thermostat and back. This is a very low voltage and you need almost all the voltage thermopile generates to open the valve.

Moisture in propane vapor; (providing this is LP and not Natural Gas)

Any moisture in the cylinder or tank will stay at the bottom. Water is heavier than petroleum products. Propane boils at extremely cold temperatures well below zero. Since the fluid in tank is always above its boiling point, it boils in the tank and only the fuel vapor exits. Any water at the bottom is not turning to vapor since it is not above its boiling point like the liquid propane. If there is any moisture escaping, it can freeze at the needle orifice in the regulator outside. This is when extra methanol is injected into fuel. There should be a drip leg on the supply line at gas valve to prevent any contaminates from entering valve. There should be no contaminating fluid in the fuel anyway to prevent cylinder or tank damage. There is methanol added to propane that boils off any water in the fuel like dry gas added to gasoline in the winter. You can get an oil residue from the odorant in the line, but this fluid would drop into the drip leg before entering valve. The drip leg is required by code.
There are many old millivolt gas valves from the 50’s still in service. In the 25 years I serviced this equipment, I may have replaced 3 or 4. And that was probably from abuse, floods, or leak around control knob when pressed in. Newer 12 or 25 volt valves with double windings and double shut off is another story. These old ones just work.

To test generator, remove red and white wires. The red is normally positive. Light pilot and hold safety knob in to keep pilot lit. Read voltage between red and white wires. That is full generated voltage with no load. When connected to valve, test voltage with pilot only lit. You will notice a slightly lower voltage. This is due to power going through the electromagnet winding for the safety valve to keep fuel open into gas valve. Then turn on thermostat and watch power drop since voltage is now also going through the main burner valve electromagnet windings. When voltage is low it may not open valve immediately. When the thermostat is turned on high resistance in the circuit can cause a delay until voltage builds up enough to pull the steel rod into the magnet coil to open valve. That is when you tap on it and this may help it open. You aren’t loosening anything in valve, you are vibrating the valve and the weak power making the magnet not as strong as it should be helps it open. (Like an old stuck solenoid on a starter that a good tap makes it work) Inside the valve is the electromagnet with coil winding also called a solenoid. Same principal, only with millivoltage.

If a electromagnet winding is shorted it will drop current to zero and safety will shut off without the power to hold the safety valve open. That is a shorted failure. When winding is open, no power travels through winding and there is no magnetic force to open valve, so valve fails in closed position. You can test winding with an ohm meter. It should read resistance through winding. Not zero, shorted; Not infinity, open.

Notice how a gas man has to be well versed in electrical circuits. Most troubleshooting is actually electrical, not always pipes, tubing, pressure and gas flow.

Next time this fails, put a jumper wire from the white wire terminal to the outer red wire. These are the thermostat wires. If it lights main burner, it is not a gas valve problem, it is low voltage losing voltage in the thermostat loop. When you take jumper off, don’t be surprised if the burner stays on. You just gave it a surge of current to open valve, and it has enough through thermostat loop to keep valve open.
(Notice the TP marking on valve is the center terminal for Thermo Pile (this powers safety valve winding) and the two outer terminals are marked TH for THermostat going to the main burner winding)

great educational write up. i hope it helps others understand.