1984 Magic Chef oven - standing pilot, but no heater pilot

[AnarchoSteff]

I have a Magic Chef oven in my 1984 Holiday Rambler. For the last couple years I've been using a Camp Chef oven for baking because I could never get the oven part of the Magic Chef to work. I recently replaced the counters and decided to make an effort to fix the **** thing.

I've been able to positively identify the primary components as being:

1) Robertshaw 4750-052 oven thermostat valve as described here
2) Robertshaw 4060-701 (4060-712 w/ pilot assembly) as described here

Chris Bryant of DeLand seemed to offer the most useful analysis of operation a few years ago.

I can push in the control knob, turn it to "pilot on" position, light the "control/standing pilot" flame, continue holding the knob depressed for 30 seconds, release the knob, and the standing pilot will stay lit, albeit ever so small. When I turn the control knob to an oven temperature position I see no change in the size of the pilot flame and it is certainly no where near the mercury filled capillary (sensor).

The way I am interpreting what I understand so far is that the thermostat oven valve has 2 positions for the pilot gas flow, "standing flame" in the "pilot on" position, and "heater flame" (slightly more open) in the oven temperature range. A slight amount of heat on the mercury filled capillary, from a standing pilot an inch or so away, will allow the pilot gas safety valve to remain open. A larger amount of heat on the capillary, such as from a heater pilot with the tip of the pilot flame in direct contact with the capillary will allow the heater gas safety valve to remain open. When the control knob is moved to an oven temperature range, two things happen, 1) the pilot valve in the oven thermostat opens slightly to allow more gas to the heater pilot flame and 2) the heater valve opens FULLY to allow gas to the burners, but keep in mind, no gas will get there until the capillary heats up enough to open the heater safety valve. The heater valve in the thermostat will close when the thermometer tells the thermostat that the temperature set on the control dial has been reached. It will open again when the temperature dips too far below a certain threshold under that temperature.

So, based on all this. My first attempt to fix this is to try to pick up either a Robertshaw 4750-052 or 4750-053 oven thermostat (only difference being the length of the temperature sensor). It seems they can be found floating around eBay for around $100 with shipping. Worst case scenario, if I have to pick up a safety valve too, I've seen the Robertshaw 4060-712 w/ pilot on eBay for around $80 w/ shipping.

I'll report back on my success/failure later.

-Steff
Kissimmee, FL

[Chris_Bryant]

I;m not at home right now, but on the older models with the mercury valve, the thermostat controls the pilot, pilot controls the burner through the safety valve.
There is a company called REPCO- http://erepco.com/ which rebuilds these controls. Might be worth a try before springing for a new range.

[j-d]

^^^ That sounds correct to me. It's been so long since I changed both of those valves, I really forget which I did first and it didn't solve the problem. Since the pilot won't "flare" from Pilot to Heater, sounds like Thermostat (the one with the Knob) is indeed the point of failure. I'm thinking that's the one I changed first, then had to go back and get the other. Could have been providential to replace both, since the mercury-charged controls started going away shortly thereafter.

And, I freely admit that I did NOT have the information that's available now, and worked with a very incomplete (non-existent, actually!) understanding of how the oven worked.

[rkentzel]

Its an oven t stat issue when your t stat lacks heater pilot changing the oven safety will not fix the problem and you will waste some cash.

[j-d]

We had that year HR with a Magic Chef stove/oven. I replaced both valves before I could get the oven to work. Paid about what you quote and that was 15 years ago. Both Thermostat (and I remember "ELOT" and using a new knob) and Control/Safety Valve work on mercury like an old glass thermometer. No Thermocouples in that that Oven. You'll be lucky to get those mercury-charged parts. The nanny agencies have banned mercury and owners of much newer stoves than yours are being told the whole appliance needs to be replaced. If you like yours and can get the valves, suggest you do so while you still can. FYI You can bank on anything Chris Bryant tells you about RV repair.

[oldtrojan66]

I knew about the mechanical aspect, but I don't disagree with your assessment, since you have in effect by-passed the low flame issue. Hope your repair is successful.

[AnarchoSteff]

I'm always open to thoughts on the topic. However, I'm quite certain it has a mercury filled capillary and NOT an electronic thermocouple. I don't believe one can purchase the capillary separate from the safety valve, and as long as the capillary line has not been damaged, I see no way for the mercury to leak out. Its the same principle as a mercury thermometer ... there's no thermoelectric effect taking place, it is purely mechanical. In order to possibly rule out the heater safety valve, I held a flame under the capillary bulb to mimic the heater pilot. It did not result in gas being expelled to the burner, which leads me more so in the direction of the thermostat.

[oldtrojan66]

Well, at the risk of stepping on someone's advice toes, I would suggest a different first step. The thermocouple is the little thing the flame goes around when it turns up a little. The oil in the bellows (the little tip inside the flame) expands and opens the safety valve. If the flame rises but does not open the safety valve (flame from main burner), the thermocouple is likely the faulty (and less expensive) part. The thermostat's job is to raise the flame size and sense the oven temp and shut off gas when temp is reached. Just my $.02 from 35 years on appliances. Hth