The short answer
A GreenLine microwave that runs cold is usually a genuine high-voltage or magnetron failure, and that makes it one of the few appliance faults where the honest answer is usually replacement. On this unit the range is assembled from catalogue parts, so the fault is nearly always a catalogue part rather than anything proprietary. Before accepting that, rule out the settings, the load and the power level, because all three mimic it exactly.
What you observe
- The turntable turns, the light is on, and nothing gets warm — The unit is running its cycle without producing energy.
- It heats weakly and takes far longer than it used to — A failing magnetron or a low supply, and both get worse rather than better.
- It heats on some power levels and not others — Power levels cycle the magnetron on and off, so this is normal behaviour misread.
- NEAR MISS: it will not start at all — That is a start fault, and the start page covers the door interlocks and supply.
Causes, most likely first on this build
- Power level set low, or a cycle that was never started — Ranked first on this build: a crowded compact panel makes a low power level easy to leave set, and this is the most common non-fault on this class.
- Vents blocked, forcing a thermal cut-out to interrupt heating — Second: blocked vents overheat the cavity and interrupt heating partway through.
- Low or shared supply voltage — Third: a shared or extended supply starves the high-voltage circuit and shows as weak heating.
- Magnetron failed or failing — Last: the likeliest of the internal causes, and a technician job rather than an owner one.
Check in this order, and why
- Check the power level is at maximum and the cycle actually started — Free, instant, and it is the commonest explanation.
- Heat a cup of water on full power for a minute and feel it — A standard test that gives an unambiguous answer about whether energy is produced.
- Plug the unit into a different circuit with nothing else on it — This separates a weak supply from a weak magnetron.
What an owner can safely check
- Move the unit to a different socket on another circuit and repeat the test — A kettle on the same circuit can be the whole story.
Tools: microwave-safe cupAbout 15 min
- Clear the vents and give the unit space at the sides and back — Boxed-in units interrupt on temperature, and the vents are owner-clearable.
Tools: vacuum, soft brushAbout 15 min
- Stop and unplug the unit if the water test is still cold — Everything remaining is inside the cabinet, and the cabinet is not an owner-serviceable space.
About 5 min
- STOP HERE, always, if the fix would need the cabinet opened — A microwave capacitor can hold a lethal charge long after unplugging. There is no owner repair inside.
Before you open anything
Safety
Never remove the outer cabinet of a microwave: the high-voltage capacitor inside can hold a lethal charge long after the unit is unplugged, and discharging it safely needs tools and training an owner does not have. Never run the unit empty, because with no load the energy has nowhere to go and the magnetron damages itself. Stop using it at once if heating stopped after a bang, a flash or a burning smell.
When to call a technician
Call, or replace, once the power level is right, the supply is sound and a cup of water stays cold, because everything left is inside the cabinet. Unplug it and stop using it immediately if the failure came with a bang, a flash or a smell of burning. Parts are ordered against the model plate rather than the badge, and on a compact build the cost of a major part sits close enough to the cost of the machine that the quote decides the repair.
Nearest pages of this class
What this page does not cover
This page covers the GreenLine microwave as a class rather than one family or model line. Magnetron and high-voltage part numbers, cavity variants, cabinet fixings and the ventilation clearances for individual installations are deliberately not here. Where a family or model page exists for your unit, it is the more specific answer and the one to read first; the nearest pages of this class are linked just above.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
