Summary

Tradespeople get called to "the fridge has stopped working" more often than most expect — landlords between tenancies, holiday let turnovers, kitchen fitters finishing an install where the client's own fridge freezer has gone warm. Most of these callouts are not refrigeration jobs at all. They're airflow, electrical, and door-seal problems that any competent multi-trade or appliance engineer can diagnose without opening the sealed refrigerant circuit.

The critical judgement call is knowing where your competence and legal authority to work stops. The compressor and refrigerant circuit are a hermetically sealed system. Opening it — even on a modern hydrocarbon (R600a/isobutane) unit — requires specific training in safe handling of flammable refrigerants, and on older HFC-charged units (R134a and similar) it requires F-Gas certification under the Fluorinated Greenhouse Gases Regulations 2015. If your fault-finding narrows the problem to "compressor not running, capacitor and relay tested good, refrigerant circuit suspect," that is the point to stop and refer on, not attempt a "regas."

This guide is written for general tradespeople, appliance engineers, and property-maintenance callouts diagnosing a domestic fridge or freezer that isn't cooling properly — not for commercial refrigeration or specialist F-Gas repair work. The goal is a fast, structured triage: is this fixable now, does it need a specialist, or is the appliance economically dead?

Key Facts

Quick Reference Table

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Symptom Most Likely Cause On-Site Fixable? Refer to Specialist?
Runs constantly, barely cold Dirty/blocked condenser coils Yes — clean coils No
Fridge warm, freezer fine (or vice versa) Evaporator fan fault, or vent duct blocked Often — fan swap Sometimes
Heavy ice build-up on back panel/evaporator Defrost heater, timer or thermistor fault Often — component swap Sometimes
Door doesn't seal, condensation inside Worn/torn door gasket Yes — gasket replacement No
Compressor silent, no hum at all No power, tripped RCD, faulty thermostat, dead compressor Sometimes Yes, if compressor confirmed dead
Compressor hums/clicks, doesn't start Failed start relay or overload protector Yes — relay swap No
Runs, but cabinet only mildly cool everywhere Overloaded with warm food, poor ventilation clearance Yes — reposition/declutter No
Hissing/gurgling then stops cooling entirely Refrigerant leak or compressor seizure No Yes — sealed-system fault
Fine in summer, poor in cold garage/outbuilding Below appliance's climate class rating Advise relocation No
Sudden total failure, burning smell Electrical/compressor winding fault No Yes — electrical/refrigeration

Detailed Guidance

Diagnostic Sequence

Work outside-in: check the simple, free things first (power, door, clearance) before assuming a component fault.

FRIDGE/FREEZER NOT COOLING PROPERLY
|
├─ Is it receiving power? (light on, display lit, listen for compressor hum)
|   |
|   ├─ NO power at all
|   |   ├─ Check socket/fuse spur/RCD — reset and retest
|   |   ├─ Check appliance flex/plug for damage
|   |   └─ If confirmed dead with power present at socket → electrical fault in appliance, refer to appliance engineer
|   |
|   └─ YES, has power
|       |
|       ├─ Compressor SILENT, no hum, no cycling
|       |   ├─ Check thermostat/control dial not set to OFF
|       |   ├─ Listen/feel for any relay click when thermostat is turned up — none = thermostat or wiring fault
|       |   └─ If thermostat and wiring test OK → suspect compressor winding fault → REFER (refrigeration/appliance specialist)
|       |
|       ├─ Compressor HUMS or CLICKS but won't start/run
|       |   ├─ Feel compressor housing — hot to touch = overload protector tripping on heat, let cool and retest
|       |   ├─ Test/swap start relay (PTC) — common failure point, low-cost part
|       |   └─ If relay/overload test good and compressor still won't start → suspect seized/locked compressor → REFER
|       |
|       └─ Compressor RUNS (audible hum, cycling normally) but cabinet not cold enough
|           ├─ Check condenser coils (rear or side) for dust/fluff build-up → clean with soft brush/vacuum
|           ├─ Check rear/side clearance from wall — minimum per manufacturer manual (commonly 25-100mm)
|           ├─ Check door seal all round with paper-grip test → replace gasket if it fails
|           ├─ Check for ice build-up on evaporator (fridge-freezer combi: usually behind rear panel in fridge compartment)
|           |   ├─ Heavy ice present → suspect defrost system: heater, timer/adaptive control, or defrost thermistor
|           |   |   └─ Manually defrost fully, test defrost heater for continuity, replace faulty component
|           |   └─ No ice, coils clean, seal good, clearance good
|           |       ├─ Check evaporator fan spins freely and runs when compressor is on (fridge compartment)
|           |       |   └─ Fan seized/silent → replace fan motor
|           |       ├─ Check condenser fan (if fitted — larger frost-free units) runs with compressor
|           |       |   └─ Fan seized/silent → replace fan motor
|           |       ├─ Check ambient location — unheated garage/outbuilding in cold weather → below climate class rating
|           |       └─ If all of the above check out and appliance still underperforms → suspect refrigerant leak/undercharge or
|           |           compressor losing capacity → REFER (sealed-system fault, do not attempt to open)
|           |
|           └─ Cabinet runs COLD but on/off cycling seems excessive or noisy
|               └─ Check door seal, overloading, and door being left ajar — user/environmental factors, not a fault

Airflow and Ventilation Faults

The single most common reason a fridge or freezer "isn't cooling" is restricted airflow at the condenser — not the compressor or refrigerant at all. Dust, pet hair, and kitchen grease accumulate on the rear coil or side-panel condenser over years, insulating it and stopping the appliance rejecting heat efficiently. This makes the compressor run far longer per cycle while achieving worse cooling. Cleaning the condenser (isolate power first, use a soft brush or vacuum with a brush attachment — never a stiff brush or water) is a five-minute job that resolves a large share of "not cold enough" callouts.

Built-in and integrated appliances are particularly prone to ventilation faults because the surrounding cabinetry can block the manufacturer's specified airflow path. Check for a ventilation grille at plinth level and a clear route for warm air to escape at the top of the housing — see integrated appliance installation for the cabinetry side of this.

Defrost System Faults

Frost-free (auto-defrost) fridge freezers periodically run a defrost heater to melt any frost off the evaporator coil, on a timer or adaptive electronic control. If the heater element fails, the timer/control fails, or the defrost thermostat (bi-metal switch that limits heater run time) fails, frost accumulates unchecked on the evaporator until it blocks airflow through the fridge or freezer compartment entirely. The classic symptom is a fridge or freezer that runs constantly, sounds like it's working hard, but the compartment is warm — with a solid block of ice visible behind the rear panel once removed.

The fix sequence: fully defrost the unit (unplug, leave doors open, towels to catch water, 24-48 hours or use a hairdryer with care), then test the defrost heater element for continuity with a multimeter, check the defrost thermostat, and check the timer/control board triggers a defrost cycle. Replacing the correct failed component (usually the heater element or the bi-metal thermostat, both inexpensive parts) resolves the fault; simply defrosting it manually without diagnosing why gives only temporary relief before it ices over again.

Door Seals and Loading

A worn, torn, or misaligned door gasket lets warm, humid air continuously infiltrate the cabinet. This both raises internal temperature and accelerates ice/frost formation, compounding a defrost fault if one is also present. Test with the paper-grip method around the whole perimeter, including the corners where seals fail first. Gaskets are a straightforward supply-and-fit replacement and should always be checked before assuming an electrical or refrigeration fault, especially on older appliances where the seal has hardened and lost its compression memory.

Overloading a fridge with warm food, packing shelves so tightly that air can't circulate internally, or leaving the door open/ajar for extended periods will all present as "not cooling properly" without any actual fault — worth ruling out with the customer before opening the appliance up.

When to Stop and Refer

Anything beyond fan motors, thermostats, relays, gaskets, and defrost components is outside general-trade scope. A compressor that has failed electrically (open or shorted windings), a refrigerant leak, or a sealed-system blockage requires a specialist with the correct refrigerant-handling competence — F-Gas certified for HFC-charged units, or hydrocarbon-safety trained for R600a units, with the correct recovery, brazing, and pressure-testing equipment. Attempting to open a sealed refrigeration circuit without this training and equipment is both a safety risk (flammable/pressurised refrigerant) and, for F-Gas refrigerants, a legal breach.

At this point the honest advice to the customer is usually a cost comparison: a specialist compressor/sealed-system repair on a domestic fridge freezer commonly runs to £150-£300 in parts and labour, against a new mid-range fridge freezer from roughly £300-£600. On an appliance already 8+ years old, replacement is very often the better advice.

Frequently Asked Questions

Can I just top up the refrigerant if the fridge is low?

No, not without the correct qualification for the refrigerant type. Domestic fridges/freezers are sealed systems — there's no service valve for topping up in normal operation. Any refrigerant work requires recovery, leak repair, evacuation and recharge by someone qualified for that refrigerant type (F-Gas certified for HFCs, hydrocarbon-safety trained for R600a). "Topping up" isn't a standard domestic repair procedure and any technician offering it without addressing the underlying leak is not doing the job properly.

The fridge is cold but the freezer compartment (or vice versa) isn't — what does that point to?

On a combined fridge freezer with a single compressor and shared refrigeration circuit, this pattern usually points to a blocked or faulty airflow path between compartments (a duct or damper fault) or a failed circulation fan in the compartment that's underperforming, rather than the compressor itself — if the compressor were failing, both compartments would typically suffer together. Check the fan and any air duct/damper first.

Is it worth repairing a fridge or freezer, or should I always recommend replacement?

Depends on age, fault, and cost. Component-level faults (fan, relay, thermostat, gasket, defrost heater) are almost always worth fixing regardless of age — they're low-cost parts. A confirmed compressor or sealed-system fault on an appliance under 5-6 years old is often worth repairing, especially if still under manufacturer warranty. On an older appliance (8+ years) with a compressor fault, replacement is usually more economical and the honest recommendation.

Does a domestic fridge freezer need an F-Gas certified engineer to service it?

Only if the work involves opening the refrigerant circuit (leak repair, recovery, recharge) on a unit charged with an F-Gas refrigerant (an HFC such as R134a). Most fridge freezers made in the last 10-15 years use R600a (isobutane), a hydrocarbon refrigerant that sits outside F-Gas Regulations but still requires trained, competent handling due to its flammability. External component work — fans, thermostats, relays, gaskets, defrost heaters — does not require any refrigerant qualification at all, since the sealed circuit is never opened.

How do I know what refrigerant is in the unit?

Check the compliance/rating plate, usually on the rear panel or inside near the salad drawer. It lists the refrigerant type and charge weight (e.g. "R600a 35g"). Never assume — always check the plate before any work that could involve the sealed system.

Regulations & Standards