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Question DetailsAsked on 11/20/2016

Main burner won't come on unless pilot light is pressed

Old homart 133-90358 wall heater. Pilot light would not stay lit. Replaced thermal coupler. Pilot light now stays lit but main burner will not come on unless pilot light knob is pressed

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7 Answers


Ahhh - good old Homarts from the 50's and possibly 60's - with a rip roaring about 40% efficiency. First learned to work on wall heaters on Homarts. Had me going for a bit there on the model number though - how I HATE how Sears reuses model numbers on things, because that model number has also been used on a cordless hedge trimmer and a chain drive garage door opener.

Anything could be right, but I THINK that number, ,especially with the 113- prefix (which is a tools department number, not HVAC) is for the optional auxiliary filter housing for the heater - because I can't find anything about a furnace/heater or furnace manual for that model number other than for an auxiliary bolt-on filter housing. Try looking for another name plate - should say Sears Roebuck Furnace Model Number 111- or 113- or similar (the Roebuck may or may not be there - was dropped in maybe the 60's), and same namplate should also have the gas pressure rating, BTU/HR rating, serial number, date of manufacture, etc. Normally was about a 2x3 to 3x4 inch riveted on metal plate - normally black painted with stamped info that came up silver (stamping through the black finish) but some Homarts I recall also had a silvery blue finish. More modern ones a clear decal with white print over silver or blue metal plate but I think Homart was a dead brand before the decals started. Unfortunately, may be on the back - was usually just above where the gas came into the unit.

As for the repair - I would say most commonly for this issue the thermocouple is not getting hot enough to turn on the main gas control valve - check the tip is well into the flame - typically 1/2 the thermocouple tip length in the blue part of the flame.

Other alternative cause with thermocouple - may not be properly seated up into the receptacle on the gas control valve - turn gas off to control valve, remove the thermocouple nut and pull it back down the thermocouple tubing a few inches, straighten the end couple inches of the thermocouple, then leaving the nut pulled back insert the thermocouple tip into the recess (gently wiggling it around) till it bottoms out snugly (making sure it is not hung up on the threads), then holding it snugly into the recess thread the retaining nut into place. Thermocouples put in with the nut commonly get cockeyed in the nut and the edges hook on the threads in the hole and therefore don't seat completely.

Now a bit more complicated possibility - if your Homart has the pilot gas tube coming off separate from the main gas valve, then on the ones I remember the main gas valve was at least sometimes relay controlled off the pilot system - so it could be your relay is shot (a commonly available part) and failing to open the main gas valve - though why pushing the pilot know down would let gas through to the main burner in that case is beyond me unless in doing so it is also making contact with the ON contacts (maybe pushing the control knob sideways or turning it a bit ?) so it is turning the main burner gas on too.

All else I can think of is a bad gas control valve (if one valve for pilot and burner) which is letting gas bypass the pilot control and get to the burner - but if that is the case I would suspect it is getting far from normal amount of gas to the burner.

Honeywell (at least a few yesars ago) made replacement gas control valves for old Homart furnaces and had a direct part number cross-over chart on their product page if you need a new one - though Sears still lists parts for Homart furnaces too.

And if you find a model number for the furnace that their system recognizes if you google the part number with the words Sears and Manual you should get several hits on both free and nominal cost parts and operating manuals online, which used to have fairly good troubleshooting instructions plus parts numbers which Sears can (hopefully) cross-reference from to current parts numbers - though I wouldnot hold my breath on gas control valves for a probably 50-60 year (old older) unit.

Here is also a chatroom discussion about your type of furnace and situation which might help - the pictures did not come up on my browser so was not real useful to me but may on yours:

As the other comment said - this is a real basic unit which while amazingly reliable (as many of the older unit were), has almost no safety measures, so I hope you have good CO alarms on each floor of the house, and of course if in a high gas cost area a new unit might well pay for itself (at 80-85%+ efficiency for economy unit, or 90%+ for high-efficiency) in 3-5 years, so if this is your "forever" house and you can afford the up-front cost, might be worth considering getting a new one - though granted the reliabilitiy or newer electronic controlled units will not come up to the reliability that your unit has probably given you.

Answered 3 years ago by LCD


It's a Sears Roebuck plate serial 110-2917 model 133-90358 with 35000 btu. I don't see a manufacturer date but there is in black at the bottom of the plate 19121-1. I might also add the pilot light knob Brome so I was turning it with a wrench as I can't seem to find any pilot light knobs anywhere. The gas line is separate from the thermal. I do get the blue flame on the main burner but when the thermostat is turned up the flame doesn't change unless the pilot light is pressed in also when the thermostat is turned off and turned back on the main burners won't come on again unless the pilot is pressed. I was wondering if it all had something to do with not having the knob? I do have it in the on position or at least it won't turn any further

Answered 3 years ago by Peggysuz


No promises - but may be if you find an old-timer in a local Heating and A/C firm that has a lot of old forced air furnace experience, they may be able to help you. Here is all else I was able to find out or guess from a bunch of research at web-based parts sites:

The 110-2917 looks like it might be a Dornback model number who made Homarts for Sears for many years - - . Now a subsidiary of another company but they still make furnaces - they might be able to help you with troubleshooting or parts.

I found a cross-reference list that showed the following possible Sears part number cross-match - the 133-90358 appears to be a catalog listing number which cross-referenced to an actual model number of 8676405 - maybe. Below is a link to the parts breakout for that unit from about late 50's or early 1960's - you could see if it looks similar -

One thing on the gas knob - many of the older furnaces had a knob with ramped surfaces on it, so the knob (and valve stem) moved up or down as it turned to the different positions - so your stem might (with the pliers) be moving only to the limit of the pilot position - might have to move up or down (always depressed in ones I have seen) a fraction of an inch as it turns to be able to turn to ON.

Other than that, assuming you are not going to be into enough bucks to start to justify a totally new unit for probably $1500-2500 installed for a normal (80%) efficiency unit, it is highly likely that a current-model gas control valve from White-Rogers, Robertshaw, or Honeywell (or others) could be used instead - might or might not need a different thermocouple or thermal pile but otherwise with possible gas tube fitting adapter should be able to replace the existing pilot and main jet valves in one unit.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services


Thanks for all the advice. I ended up buying another coupler and installing it. All is fine now. Not completely sure if it was another bad coupler or the wrong one. First coupler was universal second coupler is from Honeywell

Answered 3 years ago by Peggysuz


Well, glad you got it solved - have heard more and more reports (online and in person) of defective new thermocouples and thermopiles - usually off-brands bought at discount places or box stores, but a fair number OEM branded but made in China or Indonesia.

Another reason I stay with Honeywell for those and for all gas control applications for which Honeywell has an equivalent part - you may pay about 50% more for the part but you can count on it working for a long time.

Answered 3 years ago by LCD


One after-thought FYI, and for future readers of this thread:

Some models of thermocouples/thermopiles use the outside metal tubing (which serves as a thermal heat sink and protector for the fine wires inside) as a conductor too - so if the tubing is touching metal along it's route it can short out. Even those which do not use it for that can fail to operate properly if they touch metal, because they can pick up stray voltage from the furnace frame which messes up the very low voltage (commonly only 30 mv - 30 thousandth's of a volt with a thermocouple) from the thermocouple or thermopile - so you need to be careful in routing it that it does not touch anything between the two end connections. 

Some of those that use the outer tubing to conduct electricity also have insulated connectors at the pilot ligth bracket end - using the spring metal retainer instead of the plastic or ceramic one or a broken sleeve there, or having rust lying on the bracket can short it out. Some of that type do not have an insulated bracket, but the thermocouple itself has a ceramic or plastic sleeve molded onto it where it inserts into the bracket, so the thermocouple should not touch the bracket metal either in that type.

Also - the conductor in the center is VERY fine, so kinking or sharply bending the tubing can cause an internal short that causes the thermocouple/thermopile to fail to send its voltage to the gas valve, causing failure to operate one or both valves (pilot gas and/or main burner gas) in the valve unit.

Answered 3 years ago by LCD

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