Thermocouple issues

JohnNY1

I have a customer who pays a heating contractor to change his thermocouple every year. Every heating season his pilot light is out and un-re-lightable (is that a word?).
Any ideas why this would happen? He's got a new gas valve and pilot assembly too.

Thank you in advance.
Johnny

Steve Miller

thermocouple

The pilot pressure prolly is way too high and torching the tip. You want the pilot to engulf the top 3/8's of the tip and I try to adj. the flame to right before it starts to roar. Then I turn up the thermostate and watch it light and manually turn the valve on and off real fast and see if it blows out and if it does, adj. it slightly higher. A Standing pilot, huh? How primitive, lol, sounds like he's ready to upgrade to some higher efficient equipment anyway.

Steve M.

Greg_4

Just a 'stab', but...

1. Is pilot too forceful or t-couple placed so it is getting too overheated. (If they're heated red hot constantly, it could shorten life, but yearly??)

2. Gas valve 'sticking' or otherwise not operating smoothly causing more milivolts than when new to operate?

Two possible explanations from an "old timer" extended to me some time ago explaining possible causes of short t-couple life spans of t-couples or for one that may not be allowing gas valve to be held open during operation.

What is causing the pilot to go out? Is fuel to pilot or heating unit shut off after heating season? I'm curious, too. Maybe someone has a more plausible explanation. Greg

JohnNY1

Thanks for the input. The flame too high was my first thought. Unfortunately, it was my ONLY thought. I don't think that's the problem.
Also, I'm a BIG fan of the standing pilot.

To hell with spark ignitors!
HSI, my arse!

That's what I say.

Replacing any one of the controls associated with those ignition systems defeats the intended money-saving efficiency implied.

One man's opinion.

JohnNY1

Truth be told, I'm trying to gain a new customer here at a competitor's expense.

Customer claims:
1. New t-coup installed every year for past 6 years.
2. Last year had new gas valve installed.
3. 2 weeks later, pilot out, wouldn't relight, new pilot assy' installed at no cost.
4. Looking for service contract w/new company.

Sounds out of whack. I have no good answer.

Thanks to any who can help.

J.C.A.

Thermocouple color ?

I've been told by reliable resources that the surrounding storage(stuff that's always in the way) to a heating unit can contribute to the useful life of certain components .
The color of the cooked thermocouple could be a clue to the frequent demise. (for the life of me I can't remember the colors, or the causes but remember listening to a feverent discussion of the subject). Chris.

Gary Usa

thermocouple

hiya may i suggest something,have you replaced the t/c with a LPG one they are thicker and last longer because LPG burns hotter than natural gas,they require a thicker t/c and in effect with carry a good rating of milliamps,but need to check with the maufaturer because some need for the pilot to be turned up to produce enough milliamps to hold open the electro magnet with in the gas valve,has the gas line been tested what is the pressure drop between the gas meter and the appliance,is the gas pipe large enough for when other appliances are turned on,has the meter been timed,is the their an interupter on the t/c,

hope it may give you some room for thought on this.

take care

all the best

gary usa

Mark Hunt

Thermo-couples

> Truth be told, I'm trying to gain a new customer

> here at a competitor's expense.

>

> Customer

> claims: 1. New t-coup installed every year for

> past 6 years. 2. Last year had new gas valve

> installed. 3. 2 weeks later, pilot out, wouldn't

> relight, new pilot assy' installed at no

> cost. 4. Looking for service contract w/new

> company.

>

> Sounds out of whack. I have no good

> answer.

>

> Thanks to any who can help.





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Mark Hunt

Thermo-couples


What equipment is this? I had a problem with a particular boiler eating TC's like candy.

Turns out that there was/is a problem with the pilot tap off of that particular gas valve.

A little more info could help us narrow down the search.

Mark H

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Herb

thermocouple

life is dependant on the life of the hot junction (tip). cheap thermos have very little mass and a small hot junction so they can only be used on low output applications such as water heaters with low heat pilots. medium duty thermos have a larger hot junction so they can take the output of a modern pilot on a space heater or furnace. Heavy duty pilots have a large hot junction along with a heavy brass body to dissipate heat and should be used in the older pilot assemblies that would require an adapter to use a generic thermo. That being said you have to adjust the pilot flame (natural gas only) to avoid cooking the tip.

Unknown

Thermocouples

There are a number of things that can cause this to happen.

First thing to remember is that all pilot gas on gas valves is on line pressure. Depending on where you are located and if the system is low pressure or high pressure the pressure can vary from 6" WC to 10" WC. Put a Manometer ("U" gauge or magnehelic) on the inlet side of the gas valve and moniter the gas pressure leave it hooked up during the entire test procedure.

Make sure the pilot gas adjustment is adjusted to give you a soft blue flame hitting the upper 1/2" to 3/8" of the thermocouple. The tip should be a dull red not Bright red. Is the tip burned off (welded)?

Make sure the pilot is clean not burning yellow.

Is the cold junction of the thermocouple visibly scorched or burned. If it is then you have a combustion problem.

Make sure you have sufficient air in the room.

Is the thermocouple discolored if it has a green color that is chlorinated hydrocarbons caused by bleaches. If it is red color it is flourinated hydrocarbons caused by other chemicals. Do not discount this possibility as it can eat up a thermocouple pretty fast, that along with poor combustion.

Having done all of that take a full set of Millivolt readings:

Open Circuit (Output of T'couple) 25 to 30 Millivolts
Nothing less than 17 to 18 MV's is acceptable.

Closed Circuit 15 millivolts

Closed circuit with the burner running 15 millivolts and steady let the burner run for 15 to 20 minutes with all the covers on and doors and windows closed. Bring on all the exhaust fans in the house, also the dryer and check to make sure the flue is pulling.

Drop out after blowing pilot out less than 6 MV's normal 1 to 2.

Does this system have a redundant valve or does it have an ECO (Energy Cutoff)

Is this a boiler or a furnace? Check for CO and also check CO2 and O2.

Do a test for cracked heat exchanger.

Watch the flame for any flucuations during blower operation if a furnace.

Do you have any blocked vent switches or flame roll out switches tied into the thermocoupls circuit. You can usually tell this by a junction block on the t'couple lead.

My personal experience of working on these for the last 40 years is that frequent changes of thermocouples is caused by combustion or air problems along with contaminants. Rarely is it pressure or mechanical problems.

I have available from my catalog a full procedure for conducting these tests with illustrations. Send me an e-mail and I will send you a catalog.