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Question DetailsAsked on 12/9/2017

My weils McClain gold cga boiler pilot light goes out when i go from pilot to ON I did replace thermocoupler

My weils McClain gold cga boiler i put a new thermocoupler in i light the pilot light it lights right up i hold for a minute and switch the gas control knob to ON&it goes out. This system runs on propane any feed back would be helpful thks

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3 Answers

Voted Best Answer

Obviously, checking you have propane supply pressure, and that the gas valve on the tank is turned on - that it did not get turned off most of the way (so just enough gas in the line for the pilot but not full pressure), would be the first thing to do. Of course, if water heater or other appliance is working fine then the main supply and valve is fine - check the valve at the boiler did not somehow get bumped or played with by a kid and turned off.

When you say you hold for a minute, are you then releasing the PILOT knob (or the bypass or LIGHT button if so equipped) AND the pilot is staying lit ? If not staying lit indefinitely at that point, either thermocouple is bad (even if new - a LOT of new ones are coming in defective), it is not properly seated in the recess in the gas control valve, possibly a regulator spring in the gas control valve is bad, or you have a gas supply issue to the appliance like water in the dripleg or such.

If the pilot is staying lit fine, then you are turning the knob to ON and it goes off, a few suggestions:

1) let the pilot burn another full minute before switching to ON - sometimes the burner coming on pushes or pulls enough air past the pilot to make it waver the flame or even "walk" it off the gas supply (so it goes out). If that happens and the deflector finger and tip of the thermocouple are not hot enough to immediately reignite the pilot gas coming out, then the thermocouple can cool enough to cut off. Letting them heat up to full temp before turning gas on may solve this - assuming you have a standing pilot so this does not occur each time the boiler turns on. If you have a pilot ignitor that ignites each time the boiler wants to turn on, then go to 2) below.

2) check the draft deflector finger is properly positioned relative to the burner - it is designed to prevent 1) from happening - if turned wrong (see owner's manual) the burner coming on can blow the pilot out, or pull the pilot flame in toward the burner with the incoming combustion air as it kicks on, pulling the flame away from the thermocouple.

You should be able to visually look and see if the pilot flame is jumping around or being blown off the orifice when the burner kicks on.

3) similar to 1) and 2) if you have a thermopile (meaning boiler has LED's that run off the power from the thermocouple - usually only found on water heaters without external power supply) - it can heat up enough to let the pilot gas flow, but not enough (or be defective) so it is not putting out enough power to let the main gas flow through the regulator. Some gas regulators are designed so if the spring system in the control valve does not have enough power or gas pressure to it to operate correctly, it shuts off ALL the gas - including to the pilot.

4) If the burner comes on but very shortly thereafter goes out, I would suspect a safety cutout is functioning - like blower (either main or eductor) is not coming on, or if a direct-vent high efficiency unit, the damper in the flue is not opening when the burner want to kick on. However, some units turn them on BEFORE the burner, so in that case failure of any of them to operate properly - or a failed sensor or loose sensor wire, could prevent the burner from turning on and turn off the gas control valve.


Answered 11 months ago by LCD


Thk you for responding the pilot light does not stay lite i can light it holding the red button as soon as i release it it goes out immediately

Answered 11 months ago by Dom


Was going to give you this other similar questions with answer I did yesterday too:

Since the pilot will not stay lit, most common causes (in sort of first to last order):

1) check you have power to the unit - without power many gas control valves will not turn either pilot or burner gas on even though pushing down the override / light button allows the pilot, others will allow the pilot only to keep burning without power. Loss of power could be a power source failure, transformer failure in unit, control board failure if newer unit, safety override device tripping in newer devices, or the secondary thermostat (on a pipe outside the unit, commonly looks like a big sausage size rectangular box with 2 wires coming from it to the control box).

2) check thermostat is on HEAT / FURNACE setting rather than A/C or OFF, that the batateries are good, that desired temp is set above current temp at the thermostat - though with most (ormaybe all) units that should just stop the main burner from firing, not the pilot from lighting.

3) check manual for draft deflector finger location and orientation per previous answer, and that the tip of the thermocouple is correctly in the flame - generally they recommned the tip be at the upper tip of the blue frame, so the tip end half or so of the thermocouple is in the blue or blue-greenish (hottest) part of the flame - tip should NOT be above the blue , in the yellow or orange flame. And the flame should wrap around the thermocouple (that is why it is in at an angle to the flame), not have the flame just licking one side of it. If only on one side, the bracket (and possibly a gas tube if mounted to one) may be rotated a bit so the flame is not rising the right place. Some have a screw or bolt you have to loosen to adjust, others just have a slip sleeve you can move it in. Be gentle - you do NOT want to break off the bracket.

4) check the thermocouple is firmly in the holding bracket - some makes/models require a good electrical connection there for it to work

5) check the thermocouple tubing is not touching any other metal along the way - some holding brackets are insulated and the outer copper tubing is used as part of the circuit, so if touches the frame it shorts out and does not work right. Others it does not matter.

6) remove the thermocouple from the gas valve, straighten the last 4-6 inches or so, useflashlight and mirror or if inaccessible GENTLY stick a splinter or such up in the recess to be sure nothing is stuck in there (if you still have the old one, check the solder button on the end did not pop off and stay up in there), then slide the threaded fitting back on the thermocouple tubing so it is well clear of the end, then push the straightened button end up into the opening, making sure it goes all the way in, not hanging up on the threads (as commonly happens if the nut is around the tubing end when you put it in). Once snugly all the way up in (if in doubt use a splinter or Q-tip shaft (without the cotton on the end) to check the penetration depth of the tubing is the same as the splinter), then while holding it firmly up in by the tubing, slide the nut up and screw it in shugly - just strong finger tight of VERY, VERY gently with a wrench. Overtighten and it mushes the solder end out and shorts it out in the recess.

7) faulty thermocouple - even if new. To avoid paying $75-150 for a repairman (or double that on weekend likely) you could buy another thermocouple of different brand at HVAC or Plumbing supply or most box and hardware stores and lumber yards. I have had no trouble with Honeywells being defective from factory and only a couple of bucks more - if it works, then the replacement thermocouple was likely bad. If that is not the problem, then you spent about $10-15 and have a spare for next time you change it out.

8) one thing I do i iffy on the thermocouple/thermopile is use a propane torch (which I use anyway to initially light them) and heat the thermocouple tip with the yellow flame (blue can easily melt it) - if that makes it work then it needs more heat than the pilot flame is giving it - either thermocouple is weak (or wrong model) or the tip is not properly in the flame.

9) defective gas valve - but cost about $100-250 for that item alone plus about $100-200 labor commonly to install, and not a DIY thing for most people, so that is probably not a DIY option.

If those do not help, then I guess you have to call a repairman - or if not too cold, wait till next week for cheaper weekday rate.

Good Luck

Answered 11 months ago by LCD


OK - I may have assumed incorrectly you have done this before. You did say you are holding the knob (or the red bypass push button or whatever you have) down for a minute or so, right - to let the thermocuple come up to heaat before you release the knob.

The bypass knob (or pushing the knob down to light) lets the pilot gas flow even if the thermocouple is not lit (bypassing interior gas pressure spring-loaded safety valves in the gas control valve), thereby allowing you to manually keep the gas flowing till the thermocoupel comes up to temp. Release too soon (which can be as much as a minute or so with some units, normally more like 15-30 seconds) and the thermocouple is not hot enough so it is not generating the low voltage needed to override the safety devices in the gas control valve - so the pilot gas get cut off.

I also assumed this was (since you said thermocouple rather than thermopile) that you have a straight electric, not electronics controlled unit. If electronics controlled (has LED lights) then look in manual for what any color combination or blink pattern code it is displaying might mean.

I mentioned, way down the list, gas control valve being bad as a possibility. Some units (though not many I have run into) also require power to the gas control valve from the control box to let ANY gas through (others only require it for the main burner) so a control box failure is also a possibility. If you have a volt-ohm meter, you could check for power at the gas control valve. Type where is only needs power for main burner firing has two wire lead, type where it needs it for pilot too (which also powers the LED's that are likely on it) has 4 leads. (Leads may be individual wires or more likely two leads per wire - using a 2-conductor wire like lamp zip cord - but would have 2 or 4 connection points on the gas control valve, respectively.

Answered 11 months ago by LCD

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