Monday, September 5, 2011
Posted by RV Doctor
The Suburban oven in our older RV is acting up. The pilot lights normally and when turning the control to a cooking temperature the flame goes large and the signal to light the burner seems to be received and the main burner comes on. So far so good, it appears to be working. The problem is the oven only heats to a certain point (not even 300-degrees according to a thermometer) and the main burner goes out, acting as if it reached the temperature the control was set at. It seemed to me a problem with the safety valve/control unit or the sensor, so I started looking around for a replacement part. A few dealers tell me there is no replacement part made and I have to buy a whole new range/oven control unit. Visiting Suburban's website does not shed much light except that if there was an "A" after the model number it would be a mercury free unit. I wonder if it could be retrofitted? Gord S., Edmonton, AB
At first read, Gord, the safety valve appears to be functioning normally, assuming the delivery line pressure is set correctly. Any pro RV service facility can quickly and easily set the propane pressure for you. With correct pressure, here's what happens when you set the thermostat to any cooking temperature: When the thermostat is set to a temperature (assuming the oven pilot flame is lit), the pilot becomes slightly larger and begins to heat the thermal bulb (or a thermocouple in a non-mercury valve) attached to the safety valve. Yours appears to be doing this now. This thermal bulb, when heated by the pilot flame, expands a bellows in the safety valve and allows the propane to flow through the valve and on to the main burner where it is ignited by the extended pilot flame. This results in a time delay from when the oven thermostat is first set to a desired temperature until the main burner actually ignites. Now all that said, it is a possibility you have a faulty thermostat (main oven control valve). But first be sure the temperature sensor inside the oven is clean and free from cooking oils, oven cleaner and grease, etc., before condemning the thermostat control.
Your problem may simply be a fouled temperature sensing probe in the oven. A coated probe can send incorrect info to the oven thermostat control. If faulty, however, the thermostat and temperature sensor must indeed be replaced as a single unit since an integral capillary tube connects them. Your first task should be to clean the temperature sensor in the upper reaches of the oven. But it's also possible the oven safety valve may be the culprit. The flame sense probe (thermal probe) at the oven pilot is an integral component of the safety valve and must be replaced as a single unit like the thermostat and its temperature sense probe. I'm sure this sounds a little confusing, but a certified RV service tech should be able to quickly diagnose the problem with a few measurements and a couple of operational tests. So, clean the temperature sense probe and have the LP pressure verified keeping in mind further diagnosis may still be required. I don't believe it’s plausible, or even possible to replace a mercury safety valve with a non-mercury valve without drastically modifying the range. And it certainly is out of the realm of the do-it-yourselfer.