boiler pilot-or-thermocouple craps-out on COLDEST day; WHY?

Several years now, the thermocouple on the boiler has crapped out on only the COLDEST day (thus far) of the year.
Again this year too -- this morning, pilot was out, and it wouldn't relight. And temp outside was 17(F)!
(Window in boiler-room is open a few inches, due to air-flow problem -- we have a fan in the pipe that goes up the chimney.)
Now, in the past, replacing the thermocouple (plumber did the work) would fix it.
-----
Question: just wondering -- any substance to this apparent correlation between super-cold temperature and crap-out of thermouple?
question: would placing electric heater near the boiler possibly help?
Thanks!
David
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
David Combs wrote:

Tried to clean the contact(where the thermocouple connects to main gas valve) and tighten it? Tried to adjust pilot flame size? Tony
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Wonderful home-repair book I have shows picture of flame-size and -color, vs hitting thermocouple, and says to adjust the pilot flame-size by twisting (via screwdriver) a screwhead on the safety-thermostat body:
1: Yes, mine (honeywell) has a large screw-head available for turning (via screwdriver), but absolutely no label on it. How to be sure that's what it is?
2: No visible model-number on body of that safety-thermostat plus off-pilot-ON twist knob. So can't get on net and look for explanatory picture...
3: Worst of all, boiler-bottom is maybe three inches from floor, and pilot-flame is higher than that, under boiler, and thus CANNOT SEE THE DAMN THING!
I tried morror on extending-pole-thing, useless for my ability at manipulating maglight and mirror!
(Is gas-fire/explosion likelyhood-dangerous putting light-bulb down beneath, on floor?)
4: Plus, am 6'2" with hands to match. Tight fit.
ANY SUGGESTIONS? Especially on how to VIEW the stuff?
Also -- any TOOLS (price no issue, compared to having plumber come by each year (on COLDEST day)) that facilitate changing termocouple?
No, have not yet tried cleaning out connection. (Wife worried about playing with gas apparatus & "blow up the house!")
Thanks!
David
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Super cold weather will cause your furnace to run more often but that should not accelerate the death of the thermocouple.
Preheating the combustion air which comes from inside the house or garage (is it as cold as outside where the furnace is?) will not increase the lifetime of the thermocouple. It will only cause you to send money up the chimney.
If your furnace is located in an area subject to full outside cold air, that would be atypical and the cold temp may degrade some components due to extreme thermal expansion and metal fatigue.
Maybe its not the cold, maybe it has something to do with conditions off season (summer) like condensation that sets the stage for premature failure when usage is at its peak.
Keep a spare thermocouple on hand and learn how to replace it.
Is it an older model with a full time pilot light or a newer electronic model that ignites the pilot before igniting the main burner.
Maybe you were just unlucky.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks for the reply!!!
Have THREE spares.
Is "older" (age 7 yrs, vintage 30yrs AFTER man lands on moon!) without electronic pilot-starter.
Only problem is that due to construction of THIS (model) boiler, changing the thermocouple is difficult indeed, especially for big-handed guy.
Any equipment (or mirror-setup) to make it easier to do installation?
THANKS
David
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
David Combs wrote:

1) Coldest day of the year will cause highest draw on main gas lines. Street pressure will possibly be slightly lower than otherwise. You may have a marginal pilot flame. The pilot flame adjustment is a needle valve licated UNDER a cap screw. It is turned counter-clockwise to increase pilot flame size. The main burner has a different/separate adjustment. It is turned clockwise to increase pressure. Pilot adjustment uses a teeny-weeny pocket screwdriver to adjust it. Main burner uses a bigger screwdriver for adjustment.
2) The air from the open window may be blowing the pilot out if it is windy outside.
3) Have tech or gas company check to see if your gas pressure is adequate coming into your house.
4) Have tech use better quality thermocouple. They make good ones and cheap ones. Try a heavy duty model.
Stretch
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.