Generator brands · Home standby
Generac Home Standby Generator Repairs and Servicing
We repair and service Generac home standby generators on site across Gauteng: the engine, alternator, controller, battery and automatic transfer switch. These gas-fuelled units should start by themselves when the mains fails and hand back when it returns, so the usual complaint is a unit that did not take over during load shedding or stopped part-way through an outage.
Established 2006
20 years of experience
24/7 operations
We Arrive Within 1–2 Hours
(usually within 1 hour)
Free callouts and quotations
One-year warranty
Qualified and certified technicians
We Service & Repair All Generator Brands
All generator makes and models
1 kVA–20,000 kVA capability
Inside a Generac home standby unit
Generac is an American maker best known for automatic home standby generators such as the Guardian series. Each unit is a complete set in a weather enclosure: a spark-ignition Generac engine, an alternator driven directly by it, a controller with a small display, a starting battery, and a gas regulator and shut-off solenoid.
Smaller models use an air-cooled engine, cooled by a fan blowing over finned cylinders; larger ones are liquid-cooled with a radiator. Under the lid everything sits close together, which is why heat, leaves and nesting rodents cause more trouble here than on an open-frame set.
Generac also builds industrial sets and owns the Italian builder Pramac. This page covers the home and light commercial standby units found at Gauteng homes, small offices and shops.
What happens when the power goes off
- 01
The controller watches the mains
Sensing wires from the transfer switch tell the controller whether the mains is present. When it fails, a short delay ignores brief dips.
- 02
The engine starts and takes the load
The controller cranks the engine and opens the gas solenoid. At steady speed and voltage, the switch moves the circuits it covers to the generator: often a group of essential circuits, not the whole house.
- 03
The mains returns
Once the mains has been steady for a set time, the load goes back. The engine cools down unloaded, then stops.
- 04
The exercise run
Between outages the unit starts itself on a schedule, usually weekly, to circulate oil and prove the battery and starter. A unit that has stopped exercising is telling you something.
Common faults on Generac standby units
| Symptom | Likely causes | Repair route |
|---|---|---|
| Did not start in an outage, or warns of a low battery | Likely causesBattery past its life, charging fault, corroded terminals, unit left in OFF or manual | Repair routeBattery not charging |
| Cranks but will not run, or runs roughly | Likely causesWorn spark plugs, a blocked air filter, low gas pressure, a faulty gas solenoid | Repair routeGenerator not starting |
| Stops with a low oil pressure alarm | Likely causesOil level low after long runs, wrong grade, a faulty pressure switch, or real pressure loss | Repair routeLow oil pressure shutdown |
| Runs but the house stays dark, or will not hand back | Likely causesTransfer switch relay or contacts, sensing wiring, the unit’s own breaker tripped | Repair routeChangeover and ATS problems |
| Stops or loses power on hot afternoons | Likely causesBlocked louvres, too little clearance in a cramped corner, overload | Repair routeOverheating |
Gas supply: cylinders, bulk tanks and piped gas
Most Generac units here run on LPG from cylinders or a bulk tank; natural gas is an option only where a piped supply exists, and the unit must be set up for the gas it receives.
Cylinders turn liquid gas into vapour more slowly when cold or nearly empty, so on a Highveld winter morning a small cylinder bank may not keep up, and the unit loses power or stalls under load. More cylinder capacity or a bulk tank is the usual answer.
Pipework, wall regulators, cylinders and tanks are work for a registered LP gas installer, who issues the certificate of conformity. We check the generator side, including its gas solenoid and how it runs under load, and tell you when the symptoms point to the supply.
Why air-cooled Generac engines need closer care
With no radiator, an air-cooled engine relies on its fan pushing air over the fins and out of the enclosure, so a blocked louvre or a unit boxed in by walls or stored boxes overheats quickly.
These engines also use a little oil as they wear, and the level falls faster during long stretches of load shedding than owners expect. When outages are frequent, check the dipstick between services with the unit switched to OFF and the engine cool, and remember to set it back to AUTO afterwards.
- Louvres clear, with space around the enclosure
- Oil level checked between services, engine cool
- Unit set back to AUTO after any check
What a Generac service includes
Service intervals in the owner’s manual run by hours and by time, so a unit that only runs in outages still needs regular servicing. Heavy load shedding adds hours quickly.
- Engine oil and filter, in the grade the manual gives for the climate
- Spark plugs and air filter checked or replaced
- Valve clearances checked where the schedule calls for it
- Battery load-tested and the charging reading checked
- Coolant, hoses and fan belt on liquid-cooled models
- Enclosure cleared of leaves, nests and insects
- Exercise schedule and mode confirmed on the controller
- A simulated mains failure to prove start, transfer, hand-back and cool-down
When you book, send the model and serial numbers from the unit’s label, the hour reading and a photo of the controller screen.
Check the rating plate on an imported unit
South African homes are supplied at 230 V and 50 Hz, and Generac models built for other markets can differ. Before buying a unit, especially a second-hand or privately imported one, check that its rating plate shows a 50 Hz model suited to a 230 V supply. A mismatch is rarely a simple adjustment, because engine speed and alternator are built around the frequency; see voltage and frequency basics.
For a unit already installed, regular maintenance keeps it ready for the next outage; residential generator services covers other home standby makes, including Kohler.
Independent service
We Service & Repair All Generator Brands
Onsite Generator Repairs is an independent generator specialist. We repair, service and maintain Generac equipment as part of our work on every make of generator.
Manufacturer warranty claims go through the manufacturer’s own network. If your generator is still under warranty, check the warranty terms before arranging work by anyone else.
Brand names and trademarks belong to their respective owners. Onsite Generator Repairs is an independent service and repair company.
Service areas
Where we work in Gauteng
FAQ
Frequently asked questions
Why did my Generac not start when the power went off?
Check the controller first. It must be in AUTO, and any alarm on the screen says why it stopped. A flat battery, a closed or empty gas supply and a tripped breaker on the unit are the common simple causes. If an alarm will not clear, book a repair.
How often should a Generac be serviced?
At the running-hour interval in the owner’s manual, or the time interval if that comes first. Check the hour reading on the controller during heavy load shedding.
Can you work on the gas supply?
The supply is for a registered LP gas installer. We repair the generator, controller and transfer switch, and tell you when a fault points to the gas. See gas generators.
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- We Arrive Within 1–2 Hours (usually within 1 hour)
- Free callouts and quotations