Emergency Repair

A generator that fails to start or trips under load can bring a business to a standstill within minutes. Generators London provides 24/7 emergency generator repair across Greater London, with a direct-to-engineer phone line and a target response time of four hours to site. Our engineers carry a full complement of diagnostic equipment and common spare parts, so most faults are resolved on the first call-out.

We respond to emergency breakdowns on all makes and models of commercial and industrial generating sets, including sets we have not previously serviced. This page covers our emergency response process, the most common generator faults we repair, and the brands and kVA ratings we work on.

24/7 Emergency Response

Our emergency breakdown line on 0800 000 0000 is answered around the clock by a qualified generator engineer, not a call centre operative. When you report a breakdown, the engineer on call will ask for a description of the fault, confirm your site address and access requirements, and dispatch the nearest available technician.

We aim to have an engineer on site within four hours across Greater London. For sites within the inner boroughs or along the major arterial routes, response times are often shorter. Our vehicles are stocked with engine oils, filters, fuel system components, battery packs, AVR units and common control modules, so we carry the parts most likely to be needed before we arrive.

Clients on a planned maintenance contract receive priority emergency response, with a two-hour target response time across Greater London.

Common Generator Faults We Fix

Most commercial generator faults fall into a small number of categories. Our engineers are trained in systematic fault diagnosis and can usually identify the root cause within the first 30 minutes on site. Below are the most frequent fault types we attend.

Generator Won't Start

A failure to start is the most reported emergency fault. Common causes include a flat or failed battery, loss of fuel supply, airlocked fuel system, faulty glow plugs or heater plugs on cold-start engines, and control panel lockout due to a previously uncleared alarm. Our engineers work through a structured diagnostic sequence to identify the cause quickly and restore the set to service.

In many cases, a no-start fault is resolved within the first hour on site. Where the fault requires a part not held on the vehicle, we source and deliver it within 24 hours in most cases.

Overheating

Generator overheating is usually caused by a blocked or low coolant level, a failed thermostat, a blocked radiator, a failed coolant pump or insufficient ventilation in the generator enclosure. Overheating shutdowns are latching faults on most control systems, meaning the set will not restart until the fault has been cleared and the alarm manually reset.

We carry replacement thermostats, coolant pump impellers and coolant additives on our emergency vehicles. Where a radiator is severely blocked, we arrange an off-site clean or provide a temporary hire set to maintain power while the repair is completed.

AVR and Voltage Failure

The automatic voltage regulator (AVR) controls the alternator's field excitation to maintain a stable output voltage. A failed AVR causes the output voltage to be too high, too low or unstable, which triggers an overvoltage or undervoltage trip. AVR failure is a common fault on older sets and on sets that have been exposed to motor starting transients beyond their design tolerance.

We carry AVR units for the most common alternator brands including Stamford, Leroy Somer, Mecc Alte and Marathon. Where an exact replacement is not available on the vehicle, we source one within 24 hours. In the interim, we can confirm whether the fault is confined to the AVR or whether the alternator itself has sustained damage.

Fuel and Governor Faults

Fuel system faults include blocked fuel filters, failed lift pumps, air ingress in the fuel line, and contaminated diesel. Governor faults cause the engine to hunt, surge or run at incorrect speed, which results in unstable voltage and frequency output. Both fault types are diagnosable on site with the equipment our engineers carry.

We carry replacement fuel filters for all common engine makes, lift pump diaphragm kits, and mechanical and electronic governor components for Cummins, Perkins and Caterpillar engines. Where a fuel tank is contaminated, we recommend a fuel polish service to remove water, sludge and microbial growth before refilling.

All Makes and Models

Our emergency repair service covers all commercial and industrial generator brands, including Cummins, Perkins, Caterpillar, FG Wilson, Kohler, Sdmo, Himoinsa, Aggreko, Pramac and Broadcrown. We work on single-phase and three-phase sets from 10 kVA to over 1,000 kVA.

We also repair CHP units, UPS systems and associated ATS panels as part of our emergency response capability. If you are uncertain whether we cover your equipment type, call 0800 000 0000 and an engineer will confirm within minutes.

Frequently Asked Questions

What is your emergency response time in London?

Our target emergency response time is four hours to site across Greater London. For planned maintenance contract clients, the target is two hours. Response times are measured from the point of confirmed despatch, not from the time of your initial call. In practice, response times are often shorter for sites near our service hub or where an engineer is already in the area.

Do you charge a call-out fee for emergency repairs?

We charge a call-out fee for emergency repairs for non-contract clients. This covers travel and the first hour of diagnostic work on site. Parts and additional labour are quoted before work commences. For clients on a planned maintenance contract, emergency call-outs within the contract scope are included at no additional charge. Call 0800 000 0000 for current rates.

Can you repair a generator you have never serviced before?

Yes. We respond to emergency breakdowns on any commercial or industrial generator regardless of whether we have a previous service history for the set. Our engineers carry manufacturer data and wiring diagrams for all common brands, and our diagnostic approach is systematic so we can work on unfamiliar equipment safely and efficiently.

What if the fault cannot be fixed on the first visit?

Where a fault requires a part that is not available on the day, we source it and return as quickly as possible. If your site cannot be left without power, we can deploy a temporary hire generator to maintain supply while the repair is completed. We do not leave clients without a working solution, even if the primary set is awaiting parts.

Do you cover emergency repairs outside normal working hours?

Yes. Our emergency line on 0800 000 0000 is staffed 24 hours a day, seven days a week, including bank holidays. There is no answering service or automated system. When you call, you speak directly to a qualified engineer who can advise, despatch a technician and access your service history if you are an existing client.