Oven Only Works on High Temperature — It’s the Thermostat

An oven that heats normally at high temperatures but will not turn on at low ones points at the thermostat, not the igniter. On this Forno FFSGS6260-48 the thermostat contacts had worn and were no longer making at the low end of their range. Replacing it restored heat at every setting. $780 total.

Job details

Model: Forno FFSGS6260-48, 48-inch gas range with double oven
Symptom: Oven works at high temperature settings, does not turn on at low ones
Suspected: Failing igniter or gas supply
Actual cause: Worn oven thermostat contacts
Fix: Control area disassembled, thermostat replaced, oven tested across full range
Cost: $780, parts and labor
Location: Studio City, CA

What the customer reported

The oven worked when set to a high temperature. At lower settings nothing happened — no flame, no heat. The range top worked normally throughout.

Why this is not an igniter problem

This is the part worth understanding, because the usual suspect on a gas oven is the igniter, and here it is almost certainly not.

A weakening igniter fails the same way at every temperature. It still glows but no longer draws enough current to open the safety valve, so the oven preheats slowly or never fires — at 300 and at 450 alike. The setting does not change the behavior.

The same is true of a gas supply problem. A partially closed valve or a failing safety valve affects the oven regardless of what temperature you ask for.

So when an oven works fine at one end of the dial and is completely dead at the other, the fault has to be in the part that behaves differently depending on the setting. That narrows it to the thermostat.

What it actually was

The oven thermostat on this range is controlled directly by the temperature knob. Inside it are contacts that close to tell the oven to call for heat, and the point at which they close shifts with the knob position.

Those contacts had worn and pitted over years of use. At the high end of their travel they still closed far enough to make a connection, so the oven worked. At the low end they were no longer making contact at all, and the oven never got the signal to fire.

From the outside this looks like an oven that is half broken. Mechanically it is a worn switch.

The repair

I disassembled the control area to reach the thermostat, removed the failed unit, and installed a new one. After reassembly I tested the oven across the full range — low, mid and high settings — confirming it fired and held temperature at each.

On a 48-inch double oven range the disassembly is the bulk of the work. The part itself is straightforward; getting to it is not.

What it cost

$780 total, parts and labor included, quoted before work started. On a professional range of this size the labor reflects the disassembly and reassembly required to reach the control area.

Frequently asked questions

My oven works on high but not on low. What causes that?

Almost always the oven thermostat. Its internal contacts wear over time and stop making at the low end of the range while still working at the high end. An igniter or gas fault would affect every setting equally.

Could it be the igniter?

Unlikely with this symptom. A weak igniter makes the oven slow or unable to fire at any temperature, not selectively at low settings. If the oven is reliable at 450, the igniter is doing its job.

Is a Forno range worth repairing?

Generally yes. These are serviceable units built into openings sized for them, and the parts are available. The cost is driven by the disassembly a 48-inch double oven requires, not by the part.

Can I keep using the oven on high until it’s fixed?

It will work, but you are cooking without temperature control at the low end, and the same worn contacts will eventually fail at higher settings too. It is not dangerous, but it does not improve on its own.

Oven not heating properly?

Vertex Appliance Repair works on Forno, Wolf, Viking, Thermador and other professional ranges in West Hollywood and nearby Los Angeles neighborhoods. The $89 diagnostic is waived when you approve the repair, and completed work carries a 90-day warranty on parts and labor. See oven not heating or call 323-747-7098.