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Millivolt gas igniter questions


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I could use some education in the gas fireplace department. I don't light pilot lights for home inspection, but I operate the fireplaces by normal controls on a regular basis. Usually if the pilot light is lit or if it has electric ignition, a flip of the switch starts it up.

5 years in this house and I still don't understand my own fireplace. It is a 1990 builtin Montigo 28C propane fireplace that we never use, but it is supposedly our emergency heat source.

We had a wind storm hit us yesterday and electrical power was knocked out for everybody down our road for about 5 hours. For entertainment and hopefully heat, I pulled the 20 lb bottle off the BBQ, hooked it up to the fireplace and proceeded to bleed air out of the line. There is a push button igniter, but I found it better to just hold the pilot control in while holding a Bic lighter to the pilot light. After quite a long time with my head in the hearth, I got the pilot light lit. Then I turned the control knob to 'on'. When I flipped the remote wall switch for the flame to come, nothing happened. I turned it off, played cards for 5 mins, flipped the switch again, nothing. I left the pilot light burning and proceeded to lose at cards for an hour and a bit. At 9:30, the power came back on, thanks, guys, you deserve the overtime pay for a miserable Sunday night clearing lines. Flipped the switch to the fireplace and the stupid thing lit up all pretty and burned for about an hour like that until I shut it down for the night.

Here's what they say about Millivolt. "Millivolt ignition systems use a standing pilot light. This type of ignition system does not require any external power. Millivolt ignitions are also remote ready and can accommodate anything from a simple on/off wall switch to a programmable thermostatic remote. The pilot light can be turned off for extended periods of non-use and then re-ignited when needed. Millivolt are the most common ignition type on the market."

My question is, where does the millivolt ignition system get its power? The manufacturers hint that it generates its own power by some sort of magic.

Why did my dead fireplace refuse to light up until a bunch of time had elapsed?

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A thermopile provides the electrical current to operate the gas valve.

A thermopile converts heat energy (must have the pilot lit) to electrical power (in millivolts). Because the power production is so low this arrangement is not suitable for remote thermostats and as a result not intended to provide primary heat for a living space. It does incorporate a high limit switch to prevent overheating the unit.

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There is a push button igniter, but I found it better to just hold the pilot control in while holding a Bic lighter to the pilot light. After quite a long time with my head in the hearth, I got the pilot light lit. Then I turned the control knob to 'on'. When I flipped the remote wall switch for the flame to come, nothing happened

The ignitor is called a "piezo" ignitor.

If the ignitor doesn't easily light the gas, something is wrong, seeing as how you bled it out. The pilot hood, thermocouple/ thermopile,ignitor assembly may need to be cleaned, or you may have a bad ignitor. Check and ensure you have a good spark from the ignitor over to the pilot hood (just like you'd check for spark on a spark plug).

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My question is, where does the millivolt ignition system get its power? The manufacturers hint that it generates its own power by some sort of magic.

Why did my dead fireplace refuse to light up until a bunch of time had elapsed?

The thermopile is similar to a thermocouple in that you heat the bi metal (copper/nickel usually) which creates milli- voltage due to the temp. difference between the tip (hot junction) and lower portion (cold junction). A thermopile is basically a bunch of t-couples all grouped up.

The thermopile could be getting weak, and may not be generating much milli- voltage. It shouldn't take long for the t-pile to generate enough milli voltage to open a gas valve.

The pilot may just be dirty-- ensure there's a sharp blue flame hitting the top 3/8-1/2" of the thermopile only. If the flame is dirty, this will cause problems. If the flame hits the wrong area of the t- pile, this will cause issues.

Check for voltage drop across the wires for the switch, any limit switches, etc. A good thermopile should get somewhere in the 500-800 mv range when not under load. So, light the pilot, let it burn for 30 seconds or so, and check the reading at the 2 leads where they attach to the combination valve.

Sorry if the above couple of posts make no sense- I'm on daddy duty and bouncing back and forth....

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Thanks Bob, and Brandon, that helps a lot.

Yes, I wasn't getting a visible spark from the piezo igniter so I went with an open flame to light the pilot.

The pilot flame was a shade on the yellow side, so it could be there was not enough heat on the TP at first. The flame is hitting the top of the thermopile as shown in the manual. I downloaded and printed a manual this AM.

You gave me some things to check out.

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The pilot flame was a shade on the yellow side

The flame needs to be sharp blue. Try taking a toothbrush (no toothpase[;)]) and brushing off the inside of the hood,t-pile, etc. Then, take some compressed air and blow off the pilot assembly really well. Next, re- light the pilot and see if that helped any. If not, the pilot orifice likely needs to be cleaned.

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