Storm-season boards
Thermador Speed Oven and Microwave Repair
Microwave energy and convection heat in one built-in cavity, which means two heating systems, two failure sets and one high-voltage section nobody should open casually.
Symptoms we hear
Described as behaviour rather than as a code. We do not publish fault codes we cannot verify, and a symptom narrows a diagnosis further than a number does anyway.
- The oven runs, the light comes on and the fan turns, but nothing gets hot
- A loud hum or buzz appears only when microwave power is called for
- The convection side works normally and the microwave side does not
- The door has to be lifted or pushed to make the oven accept a start
- The cavity heats unevenly with cold centres in reheated food
- The unit shuts off partway through a cycle and will not restart until it cools
- The touch panel is unresponsive in one area of the keypad
- A burning or electrical smell during microwave operation
What actually fails
- Door interlock switches, which are the most common reason a speed oven runs without heating
- The magnetron and its high-voltage supply, including the diode and capacitor
- Cooling fans and blocked cabinet vents, which cause thermal cutouts partway through a cycle
- Convection elements and fan motors on the conventional side of the cavity
- Touch control panels and the ribbon connections behind them
- Waveguide covers that char and arc after grease or food splash builds up
Two ovens sharing one cavity
A speed oven combines microwave energy with convection heat so that a single built-in unit can reheat in ninety seconds and roast properly an hour later. Mechanically it is two appliances that happen to share a door, a cavity and a control panel, and that is genuinely useful when diagnosing a fault, because the first question splits the machine cleanly in half.
If convection works and microwave does not, the fault is in the high-voltage section, the interlocks or the control that switches them. If microwave works and convection does not, we are looking at an element, a fan motor or a thermal limit. If neither works, we are looking at supply, the main board or the interface. Owners often supply that answer themselves without realising it.
The interlocks come first, every time
The most common speed oven complaint we take is that the unit lights up, the turntable or the fan runs, the timer counts down, and the food comes out cold. That is a classic no-heat pattern and its usual cause is the door interlock system rather than the magnetron.
Every microwave-capable oven has multiple switches that must agree the door is closed. They are cheap, they are mechanical, and they take the impact of every door slam over ten years. When one drifts out of adjustment or fails, the control logic prevents microwave output while allowing everything else to run. It looks catastrophic and it usually is not. If your door needs a nudge or a lift before the oven accepts a start, tell us on the phone, because that detail is diagnostic.
The part of this appliance that is genuinely dangerous
The high-voltage section of a microwave-capable oven holds enough stored energy in its capacitor to injure or kill after the unit is unplugged. There is no safe way for a homeowner to test that section, and there is no meaningful troubleshoot to attempt with the case off. If your speed oven is humming loudly, smells of burning, or has visible arcing inside the cavity, switch it off at the breaker and leave it alone until someone competent has it open.
Arcing in the cavity usually traces to a damaged waveguide cover. It is a small part and an inexpensive one, but running the oven with it charred will damage things that are neither.
Built in, so access is half the job
Speed ovens are installed into a cabinet stack, often above or below a wall oven, and frequently with a stone or tile surround that was fitted afterward. Getting one out is a controlled operation, not a pull. We check the trim, the fixings and the supply slack before we start, and where the surround makes removal genuinely risky we tell you before we begin rather than after something has chipped.
Ventilation matters here too. These units reject heat into the cabinet, and a stack that has been closed up or insulated will cause thermal shutdowns partway through longer cycles. That fault looks like an intermittent electronics problem and is not one.
Terms
Flat $129 diagnostic, credited toward the repair when you approve the work. Written estimate before any part is ordered or fitted. Genuine OEM parts through the BSH distribution channel shared with Bosch and Gaggenau, 90 days on labour, 365 days on parts. Appointments Monday to Friday 8am to 6pm and Saturday 9am to 4pm. We are an independent repair company and are not affiliated with or authorized by the manufacturer.
Local factor
Storm-season boards
Around 68 thunderstorm days a year put repeated transient stress on control boards and power supplies.
Which is why the first questions on a call are where the appliance is installed and how long it has been there, not which model it is.
How the visit works
Diagnostic
$129 flat diagnostic, credited toward the repair when you approve the work.
Estimate
A written estimate comes before any part is ordered or fitted. How pricing works
Warranty
90 days labour, 365 days parts, genuine OEM components. Warranty terms
Parts
Genuine OEM parts, ordered through the same BSH distribution channel that serves Thermador, Bosch and Gaggenau.
Customer reviews
4.3 out of 5, across 42 customer reviews
After a speed ovens visit
Each entry is one visit: what failed, what was measured, what was changed. They are printed as they were given to us, and the less flattering ones are printed too.
Our combination unit was tripping the breaker whenever microwave and convection ran together. He found a shorted fan motor loading the circuit. Replaced, and it has run since, but I am watching it.
Delphine C.2025-07-24
The unit would run and the plate would turn but nothing heated. He measured the magnetron and the high voltage capacitor, found the capacitor failed, replaced it and checked the interlocks after.
Casper B.2025-08-07
He fixed the fault, a failed door interlock switch, and it works. The unit was refitted slightly proud of the cabinet and I had to ask twice before somebody came back and sat it properly.
Emmett D.2025-07-10
Where this comes up
Areas that name this appliance class, hardest published water first.
12 mi by road · 20 min
Nocatee
22 mi by road · 35 min
Ponte Vedra Beach
22 mi by road · 30 min
Palencia
13 mi by road · 22 min
Deerwood
18 mi by road · 26 min
World Golf Village
3 mi by road · 8 min
Fruit Cove
Read first
Articles covering this appliance class, pulled from their own frontmatter.
6 min read
Before you call
Some faults are not faults. A short list of checks worth doing first, and the details that make a diagnostic visit faster and cheaper when one is needed.
6 min read
Storms and control boards
This region averages about 68 thunderstorm days a year. Why appliance boards fail in clusters afterwards, and how to tell a dead board from a supply fault.
5 min read
Dead after self-clean
A wall oven that completes a clean cycle and then goes completely dead is a recognisable fault with a recognisable cause. What opened, and why it opened.
6 min read
Steam oven makes no steam
Weak steam has four separable causes: heat, fill, level sensing and the door seal. How a technician tells them apart before replacing a steam generator.
7 min read
Model and serial numbers
A model number that stayed in production for years did not stay identical. Where to find the data plate on each built-in class, and what the serial decides.
Related appliances
Wall ovens
Built into cabinetry, carrying a heavy door and a lot of heat. Wall ovens fail at the door, at the sensor and at whatever the last self-clean cycle pushed too far.
Steam ovens
A small water system inside an oven: fill, heat, level sensing, drain and a sealed door. Weak steam is one of those five, and they are separable in an hour.
Ventilation
Hoods, inline blowers and roof-mounted units. The motor is often nowhere near the kitchen, and on the coast it is sitting in salt air all year.
Induction cooktops
Full-surface induction is an electronics platform under a sheet of glass. When a zone dies it is almost never an element, and diagnosis has to start at the inverter boards.
Independent, and saying so plainly
Meridian Appliance Works is an independent service company. We are not affiliated with, authorized by, or endorsed by Thermador or BSH Home Appliances. We are not a Thermador service centre and we do not hold or claim any Thermador or BSH Home Appliances accreditation. We name the brand only to say which appliances we work on.
Meridian Appliance Works is an independent appliance repair company. We are not affiliated with, authorized by, or endorsed by Thermador or its parent company. All brand names and model numbers are the property of their respective owners and are used only to identify the appliances we service.
Next step
Book a diagnostic
Tell us the appliance and what it is doing. We will give you a written estimate before anything is ordered.
Mon–Fri 8am–6pm · Sat 9am–4pm
Request a visit- $129 flat diagnostic, credited toward the repair when you approve the work.
- 90 days labour, 365 days parts, genuine OEM components.