Walk-In Cold Room Troubleshooting: Diagnose & Fix Common Faults (UK 2026)
Quick snapshot: Walk-in cold rooms fail for 8 main reasons. 60% can be diagnosed with visual checks; 40% need F-Gas certified engineers. Modern units cost £4,000–£12,000 to replace; typical repair callouts £200–£500. Units older than 10 years using R404A refrigerant are becoming uneconomic as of the 2020 HFC restrictions.
- Door seals fail first: 35% of “cold room not cooling” complaints trace to worn gaskets—fix £80–£200
- F-Gas certification is mandatory: Any refrigerant work requires FGAS-registered engineer; DIY venting breaches EPA regulations
- Defrost cycle failure freezes evaporators: Ice build-up reduces cooling capacity by 30–50% within 48 hours
- Condenser blockage mimics low refrigerant: Clean fins cost £40; misdiagnosis can waste £500+ on unnecessary recharge
- R404A units hit obsolescence Jan 2020: Virgin HFC with GWP >2500 banned for repair; retrofit to R290 costs £3,000–£5,000
- Drain clogs cause mould + water damage: Stagnant water in drain trap ruins panel insulation (£2,000+ replacement)
- Compressor runtime >22 hours/day signals failure: Normal duty = 16–18 hours; continuous running kills motor within weeks
- Repair vs replace threshold = 5–7 years lifespan: Units older than 10 years justify planned replacement over emergency fixes
In This Guide
- Cold room not cooling / temperature drifting up
- Ice build-up on evaporator / panels
- Compressor running constantly
- Strange noises (knock, rattle, hum)
- Water on floor / dripping
- Door won’t close properly
- Lights not working / power supply issues
- Smell / mildew inside cabinet
- Brand-specific diagnostic notes
- F-Gas compliance & safety
- Repair vs replace decision matrix
Symptom 1: Cold Room Not Cooling / Temperature Drifting Up
Early signs: Temperature gauge reading 6–8°C instead of 2–4°C. Interior feels warmer than usual. Takes longer to chill food. Condensation on cabinet walls (humidity rising).
Diagnostic Flow
Close door. Run a torch inside at night; if you see light leaking around the frame, the gasket is failed or misaligned. Push on door; it should seal with moderate pressure, not swing loose. Cost to fix: £80–£200 (gasket + labour, 30 mins). Gasket typically lasts 5–7 years; replacement every 2–3 years in busy kitchens common.
Leave door open for 5 seconds, then close. Does it swing open? Sign of hinge sag or floor slope. Measure temperature inside 10 minutes after closing: if it doesn’t drop by 1–2°C, heat ingress is severe. Don’t proceed with refrigerant diagnosis until seal is ruled out.
Locate condenser unit (usually rear or side of cabinet). Shine torch between fins. Dust and grease block airflow, causing compressor to work harder with slower cooling. Gently brush fins with soft brush or use compressed air (not high-pressure hose—risk of crimping). If condenser is oily, compressor is likely weeping oil; call engineer. Cost of clean: £40 (DIY) to £100 (engineer).
Turn off the unit. Wait 2 minutes for pressure to equalise. Switch back on. Compressor should start with a steady hum, building to normal running sound within 30 seconds. If it stutters, clicks, or makes grinding sounds, internal damage likely. Cost: compressor replacement £1,200–£2,500 + labour + regas.
If all 4 checks pass: Problem is likely refrigerant leak or expansion valve fault. Call F-Gas engineer. Cost: £250 callout + diagnosis. If leak found, expect £400–£600 repair (includes location, repair, recharge, retest). If expansion valve: £600–£900.
Decision point: If unit is >8 years old with R404A refrigerant, engineer may recommend retrofit to R290 (£3,000–£5,000) rather than chase small leaks on soon-to-be-banned refrigerant. Get quote for both repair and retrofit before approving work.
Symptom 2: Ice Build-Up on Evaporator / Panels
Early signs: Frost accumulation on back wall or ceiling. Reduced airflow (fan running but weak cooling). Ice layer growing visibly each shift. Eventually compressor cycles on/off rapidly or runs non-stop fighting ice load.
What’s Happening
Defrost cycle removes ice automatically (usually nightly, 2–4 hours). If defrost fails—thermostat malfunction, timer stuck, or electric heater dead—ice won’t melt and blocks airflow. Within 48 hours, cooling capacity drops 30–50%.
Diagnostic Flow
Look for “Defrost” or “Cycle” button on control unit (Foster units: pull knob on right side). Initiate defrost manually. Fan should stop; heating element (if visible under evaporator cover) should warm up. Wait 30 minutes. Ice should drip as water toward drain. If nothing happens, thermostat is stuck or heater is dead. Cost: thermostat £150–£300; heating element £200–£450.
Follow condensate drain line from evaporator toward exterior or sump. Locate drain hole (usually 10mm diameter). Blow compressed air through it; water should emerge freely. If blocked, thaw ice and flush drain with hot water + soft brush. Cost: DIY (free) or £50–£80 engineer assist. Don’t ignore: frozen drain causes water to back up into insulation panels.
Record time of automatic defrost (check control panel log or ask kitchen staff). Observe whether compressor stops, heater activates, and ice visibly reduces. If defrost runs but ice persists, heater output is too low (common fault). If defrost doesn’t run at all, timer is failed. Cost: timer replacement £180–£350.
If defrost system is serviceable: Manually defrost immediately (never chip ice—risk to pipes). Schedule professional inspection of thermostat and timer within 1 week. Cost: diagnostic visit £150–£200.
If defrost heater is dead: Unit won’t cool until fixed. This is urgent. Call engineer same day. Expect downtime 2–4 hours. Cost: heater element + labour £300–£600.
Symptom 3: Compressor Running Constantly (Never Stops)
Early signs: Compressor hum continuous 24/7. Temperature inside still won’t drop below 5–6°C. Unit sounds “stressed” (high-pitched whine or laboured tone). Monthly electricity bill 20–30% higher than normal.
Root Cause Analysis
Compressor should cycle: 16–18 hours running per 24-hour day (roughly 70% duty). Continuous running signals it’s trying to reach setpoint but can’t. Five common causes:
- Refrigerant low (slow leak): Compressor keeps running because cooling capacity is reduced. Takes longer to reach setpoint. Most common post-warranty issue.
- Condenser blocked with dust/grease: Heat isn’t being rejected efficiently. Compressor has to run harder, longer.
- Door seal leaking (heat ingress): Cold air escaping; compressor chases rising temp.
- Setpoint temperature too low: User set to 0°C instead of 2–4°C. Unit runs endlessly trying to reach unrealistic target.
- Interior lights on continuously: Heat load in cabinet exceeds compressor capacity. Rare but possible in kitchens with lights left on 24/7.
Diagnostic Checks (30 minutes, no tools needed)
After checks 1–5: If compressor still running constantly and temp won’t stabilise at setpoint, refrigerant is low or expansion valve is stuck. Call F-Gas engineer. Cost: diagnostic £150–£200; recharge £400–£600 (if small leak found and sealed); expansion valve replacement £700–£950.
Cost of continuous running: Compressor lifespan is typically 10–12 years at normal duty (70% runtime). Continuous running burns through the motor in 12–24 months. Act fast.
Symptom 4: Strange Noises (Knock, Rattle, Hum, Flutter)
Early signs: Unusual sounds during compressor operation. Knocking: repetitive bang every 2–3 seconds. Rattle: loose metal parts vibrating. Hum with high pitch: motor bearing strain. Flutter: rhythmic clicking from evaporator area.
Diagnostic Flow
Turn off compressor. Feel around compressor housing for loose bolts (use adjustable wrench, snug gently—don’t over-tighten). Listen during next startup. If knock stops: bolts were the culprit. Cost: free DIY fix. Check quarterly in future.
If rattle comes from interior, fan blade may be bent. Open evaporator access panel (different per brand—see manual). Spin fan by hand. Blade should clear cover with 5mm clearance all round. If it’s rubbing, fan is bent. Cost: fan blade replacement £80–£200. If cover itself is loose, tighten mounting bolts.
Compressor should sit on rubber mounts (usually 4 feet). If mounts are perished (cracked, collapsed), compressor vibrates against cabinet frame. Look underneath/behind unit. Perished rubber = metal-to-metal contact. Cost: mounting pads £150–£350 + labour 1–2 hours.
If compressor emits persistent high whine that increases in pitch, internal bearing is failing. This escalates rapidly. Do not delay. Call engineer immediately. Cost: compressor replacement £1,200–£2,500 + labour. Continuing to run a failing bearing can seize the motor suddenly, leaving no choice but full replacement.
Flutter/clicking from expansion valve area: Refrigerant cavitation (liquid refrigerant partially vaporising in the expansion valve due to low suction pressure or blockage). This means low charge or metering problem. Call engineer. Cost: diagnostic £150 + repair £400–£700.
Noises are early warning signs. Don’t ignore them hoping they’ll go away. A few days of vibration or rubbing can cause £1,000+ damage to adjacent components.
Symptom 5: Water on Floor / Dripping Inside Cabinet
Early signs: Puddle under unit. Water dripping from drain line (if external) or weeping from cabinet walls. Musty smell developing. Floors becoming slippery.
Diagnostic Flow
Locate condensate drain (usually a 10–15mm pipe exiting cabinet, routed to external drain or sump). Hold small container under drain outlet. Pour warm water (not boiling) down the interior drain tray or evaporator housing. Water should flow out the outlet within 10 seconds. If backing up: drain is blocked. Cost: clearing £50–£120 (DIY with plumbing snake or enzyme drain cleaner; avoid caustic—risk to rubber seals).
In cold climates, drain lines can freeze if routed externally without insulation. Trace drain to outlet. If ice visible, apply warm (not hot) water bottle or heat tape to thaw. Cost: heat trace tape £30–£60 to prevent recurrence; re-route drain inside kitchen if possible (£150–£300 labour).
If water is leaking from panel walls (not from drain outlet), insulation may be water-logged. This is expensive. Open an access panel or drill a small inspection hole in rear panel (low, inconspicuous spot). If inside is dark, wet foam: insulation is ruined. Cost: single panel replacement £1,500–£3,000 (depending on size); full cabinet rebuild £5,000+. Call engineer for assessment before DIY drilling.
Stagnant water in drain traps breeds mould and pathogenic bacteria. After clearing blockage, flush trap with 1:10 bleach solution (or proprietary food-safe sanitiser), let sit 10 minutes, flush with hot water. Cost: sanitiser £10–£25.
Water ingress into panels is NOT reversible. Once foam absorbs water, insulation value is lost permanently; mould colonisation is inevitable. If panel water-logging is confirmed, budget for panel replacement within 6 months before thermal performance degrades further and compressor has to overwork.
For recurring drain blockages: Consider installing condensate pump (if unit doesn’t have one). Cost: pump + plumbing £400–£600. Pump automatically cycles standing water out, preventing stagnation and mould.
Symptom 6: Door Won’t Close Properly
Early signs: Door swings open when you release it. Gap visible around frame. Squeaking or grinding noise when closing. Magnetic latch won’t engage.
Diagnostic Flow
Place spirit level on floor inside unit. If off-level by >10mm, door will swing open due to gravity. Walk-in floors should be sloped slightly toward drain; excessive slope causes closure problems. Cost: shim under feet £0–£50 (DIY); professional floor levelling (rare, usually not worth cost). Temporary fix: wedge under door (unsafe long-term).
Open door slowly, watching how it moves. Should swing smoothly, no binding. If door sags (top corner pulling away from frame), hinges are stretched or bolts loose. Tighten hinge bolts (usually M8 or M10). If bolts won’t tighten further, hole is stripped; cost £120–£250 to rethread or replace hinge assembly.
Close door, listen for magnetic click. Latch should pull door tight. If no click or weak engagement, magnet is weak or misaligned. Inspect magnetic catch (usually cylindrical, top corner of frame). If misaligned, loosen mounting bolts, reposition slightly, retighten. Cost: magnetic catch replacement £60–£140.
Vinyl strip curtain blocking door? Bunched, twisted, or frayed strips prevent clean closure. Cost: strip replacement £80–£180. Also check for ice on strips (defrost cycles should prevent this; if recurrent, defrost timer may be slow).
Safety note: A door that won’t close is a MAJOR food safety issue. EHO will flag it immediately on inspection. If door won’t stay closed, make safe (prop open or use temporary wedge) and schedule hinge or latch repair within 48 hours. A cold room with a gaping door will fail temperature monitoring.
Symptom 7: Lights Not Working / Power Supply Issues
Early signs: Interior lights won’t turn on. Unit won’t power up at all. Intermittent power (compressor cycles on/off unexpectedly). Alarm lights on control panel.
Diagnostic Flow
Most walk-ins plug into standard 13A wall socket or hardwired to DB. If unit won’t power on, check if RCD breaker (usually red/reset button on wall socket or building board) has tripped. Press reset. If it trips immediately when you plug in unit, suspect short circuit or water damage. Do NOT force. Cost: sparky inspection £80–£150.
If compressor runs but interior lights are out: check bulb. Old fluorescent tubes fail first; cost £15–£40 replacement (or LED retrofit £30–£80 for equivalent brightness, lower heat). Bayonet or screw fitting? Ensure replacement matches.
Some units have door-actuated micro-switch: pressing door interrupts circuit, lights off. If lights always off, micro-switch may be stuck or wired reversed. Cost: switch replacement £40–£100; rewire £100–£200.
If red warning light is on (usually “high temp” or “fault”), compressor may be running but thermal cut-out has engaged because cabinet over-temp. This requires engineer diagnosis (could be low refrigerant, failed sensor, stuck valve). Cost: diagnostic £150–£200.
Walk-in should have annual Portable Appliance Test (PAT test) certificate. If overdue, electrical safety cannot be guaranteed. Cost: PAT test £40–£80. If test fails, fault will be identified and quoted separately.
Rule out power cord damage: If unit is portable (wheeled), check power cable for cuts, crushed insulation, or signs of overheating (discolouration). Cost: power cord replacement £80–£150.
Electrical work must be done by qualified electrician or FGAS engineer with electrical endorsement. Don’t attempt rewiring yourself.
Symptom 8: Smell / Mildew Inside Cabinet
Early signs: Musty odour even after cleaning. Smell stronger after humid weather or if door left open. Black spots (mould) visible on walls or drain area.
Root Causes & Solutions
Cause A: Stagnant water in drain trap
- Drain collects condensate 24/7. If drain blockage backs up water (even slightly), it sits stagnant and breeds Legionella and mould.
- Solution: Clear drain (see Symptom 5). Flush with 1:10 bleach solution. Repeat monthly. Cost: £0 (DIY) to £80 (engineer assist).
Cause B: Spilled product (milk, fish blood, raw meat juices)
- If food product spilled and not immediately cleaned, bacteria colonise floor, walls, drain. Smell intensifies.
- Solution: Empty unit completely. Damp wipe all surfaces with 1:10 bleach solution. Pay special attention to drain area, corners, and under shelving. Dry thoroughly. Restock. Cost: 2–3 hours labour + cleaning materials (£30–£60). If smell persists, mould has penetrated panel. See Cause C.
Cause C: Mould in panels (after door left open or humidity spike)
- If door left open during humid weather (summer), warm moist air infiltrates insulation. Mould colonises foam within 48 hours.
- Solution: Run unit at full capacity (close door, set to 1–2°C) for 5–7 days. Dehumidification and low temp will slow mould. Simultaneously, clean interior and sanitise. If smell persists after 1 week, mould is deep in panels. Cost: charcoal filter retrofit £150–£250 (absorbs odours but doesn’t kill mould); or panel replacement £1,500–£3,000 for mould-affected section.
Prevention & ongoing management:
Brand-Specific Diagnostic Notes
| Brand | Control Panel | Common Issues | Parts Availability | Typical Callout Cost |
|---|---|---|---|---|
| Foster Coolroom | Proprietary 7–12 button panel. Knob-style cycle selector. | Thermostat drift (reads 1–2°C higher than actual); door latch sticking on older units (post-2015 improved). | Excellent. Parts stock in UK. 2–3 day lead common. | £200–£280 |
| Coolzone (Modular Kit) | Varies by spec. PLC-based on newer models; analogue dial on basic units. | Panel connector corrosion (humid kitchens); evaporator fan failure post-warranty. Modular design = easy panel swap. | Good for standard panels; custom specs 7–10 days. | £220–£300 |
| Misa (Italian Build) | Simple analogue thermostat + relay. Rarely electronic. | Gasket material quality varies; hinge bolts loosen (tighten M8 bolts quarterly). Durable but slow to repair out-of-warranty. | Poor. Parts often special order from Italy. 10–15 day lead typical. | £250–£350 (includes hold time) |
| Williams (UK Service Network) | Robust digital controller or analogue dial. Easy to access. | Condenser fin corrosion in salty air environments (coastal kitchens). Compressor isolation bolts loosen. | Excellent. UK distributor holds major parts. 1–2 day lead. | £180–£250 |
| AC Refrigeration (Bespoke) | Custom control unit; varies widely. May use third-party components. | Since each build is custom, fault diagnosis requires original installer knowledge. Door seal sourcing difficult if panel geometry is non-standard. | Very poor. Often must source from original installer (may have closed). Lead times: 4–8 weeks or longer. | £300–£500+ (diagnostic complex) |
Key takeaway for multi-brand environments: Foster and Williams have national service networks; Misa, Coolzone, and especially AC Refrigeration require patience with lead times. If you operate multiple brands, standardise on Foster or Williams for future purchases to minimise spare parts fragmentation and support complexity.
F-Gas Compliance & Safety
What Is F-Gas Regulation?
F-Gas (Fluorinated Gases Regulation EU 517/2014, adopted into UK law) restricts use, servicing, and disposal of fluorinated refrigerants. Key rules for walk-in operators:
F-Gas Safety Checklist
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Keep FGAS certificate on file: Every service report from an engineer should include their FGAS reg number. File it. If you’re audited by EHO or insurance, this proves compliance.
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Annual leak test mandatory: Schedule (not optional). Cost: £80–£150. Protects environment and keeps your unit legal.
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If unit is R404A and >5 years old: Budget for retrofit or replacement within 18–24 months. Don’t wait for emergency failure. Planned work is far cheaper than emergency callout + repair + retrofit stress.
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Never attempt DIY refrigerant work. It’s illegal AND dangerous (refrigerant is toxic; incorrect handling can cause frostbite, respiratory damage). Always call FGAS engineer.
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Electrical work: Any work on control electronics, power supply, or internal wiring should be done by a qualified electrician. FGAS engineers are refrigeration specialists; ask for electrical endorsement if they’re handling electrics.
Repair vs Replace Decision Matrix
When a walk-in fails, the first question is: fix it or replace it? Here’s a framework:
| Age (Years) | Refrigerant Type | Fault Severity | Recommendation | Typical Economics |
|---|---|---|---|---|
| 0–3 | Any (R290/R744 modern) | Any single fault | REPAIR. Warranty still active; repair cost low relative to remaining lifespan. | Repair £200–£800. Replacement £6,000–£12,000. ROI: repair wins. |
| 3–5 | R290/R744 | Minor (seal, drain, fan blade) | REPAIR. Warranty expiring; low-cost fixes still economical. | Repair £100–£400. Keep another 5+ years easy. |
| 3–5 | R290/R744 | Major (compressor, heater, timer) | REPAIR unless >£1,500. If repair >£1,500, quote replacement. 5 years = 50% lifespan remaining; replacement justifiable if repair costs 40%+ of new unit. | Compressor = £1,200+. Weigh: pay £1,500 repair or £8,000 replacement? If age 3, repair. If age 4.5, consider replacement. |
| 5–7 | R290/R744 | Minor | REPAIR. Unit still mid-lifespan. Fix and move on. | Repair £200–£600. Replacement not yet justified. |
| 5–7 | R290/R744 | Major | GET BOTH QUOTES. If repair >£2,000, replacement is competitive. Modern unit saves 15–20% energy vs. aging unit. | Repair £2,000+. Replacement £7,000–£11,000. If repair = £2,500, split difference suggests replacement. New unit also means warranty, better efficiency, lower electricity. |
| 5–10 | R404A | Minor | REPAIR with caveat. Budget retrofit to R290 within 18 months. Single repairs on R404A are short-term fixes. | Repair £200–£500 now. Retrofit £3,000–£5,000 in 18 months. Total cost of keeping R404A alive: £3,500–£6,000. |
| 5–10 | R404A | Major | REPLACEMENT RECOMMENDED. Repairing R404A units past 7 years is economically poor. January 2020 phase-out looms. Retrofit cost + repair cost = replacement cost soon anyway. | Repair £1,500–£2,500. Retrofit if continued use = £3,000–£5,000. Total: £4,500–£7,500. New unit: £7,000–£11,000 (but lasts 10+ years warranty). |
| 10+ | Any | Any | REPLACEMENT. Unit is at/beyond design lifespan. Even minor repair defers inevitable replacement, increasing total cost. Compressor efficiency drops 5–10% per year after 10 years; electricity costs climb. | Repair now: £200–£1,500. Replacement deferred 1–2 years: additional repair costs £300–£1,000. Replacement cost compounds. Plan replacement now, phase out old unit. |
Energy efficiency gain from new unit (10+ year old → modern): Roughly 15–25% electricity saving due to improved compressor design, better insulation, and modern refrigerants. Over 10 years, this pays for much of the replacement cost. A unit paying £100/week in electricity (old, inefficient) might drop to £75/week (new, efficient). Difference: £1,300/year × 10 = £13,000 saved. Replacement cost of £9,000 is recovered in 7 years.
Cost-of-Ownership Snapshot (10-Year Horizon)
Related Guides & Resources
- Walk-In Cold Room Buying Guide 2026 — Spec comparison, size calculation, ROI analysis
- Blast Chiller Troubleshooting — Fault diagnostics for rapid-chill equipment
- Refrigerated Prep Counter Maintenance — Care schedule for undercounter units
- Refrigeration Energy Efficiency Guide — Cut electricity 15–25% with operational tweaks
Walk-in cold room faults follow a predictable diagnostic pattern across all brands. 60% can be ruled in or out with visual checks (door seal, condenser, drain, compressor bolts) in under 30 minutes. Remaining 40% require F-Gas certified engineer (£200–£300 callout). Most common repairs cost £200–£800; major faults (compressor, heater, panel water ingress) cost £1,200–£3,000. Units older than 10 years justify replacement based on energy savings alone (15–25% electricity reduction). R404A units face January 2020 phase-out of virgin refrigerant; budget retrofit (£3,000–£5,000) or replacement within 18 months. Always call FGAS engineer for refrigerant work; never attempt DIY. Proper drain maintenance and monthly sanitisation prevent 70% of recurring odour and mould issues.
Frequently Asked Questions
Annual service is standard. This includes leak detection, control system check, and gasket inspection. Twice-yearly service recommended in high-use kitchens (hospitals, central production kitchens) running 24/7. Cost: £150–£250 per visit.
You can DIY: door gasket cleaning, condenser fin brushing, drain clearing, and tightening compressor bolts. You CANNOT DIY: refrigerant work, electrical rewiring, or control system repairs—these require licensed engineers. Attempting unlicensed work voids warranty and breaches F-Gas law.
Compressor replacement typically costs £1,200–£2,500 for the compressor itself, plus £400–£600 for labour, evacuation, recharge, and testing. Total: £1,600–£3,100. If multiple components are damaged (oil contamination spreading), total cost can reach £3,500+. Always get a quote before approving work.
Yes, existing R404A units can continue operating. However, virgin R404A cannot be purchased for servicing from 1 January 2020. You must use recovered/recycled R404A (limited supply, rising cost) or retrofit to R290 (£3,000–£5,000). New charges with virgin gas are illegal. Plan ahead if you own R404A units.
Door seal failure: light visible around door frame when closed; temperature drifts up slowly over days. Low refrigerant: no visible gap; temperature stable for a few hours then drifts up slowly. Quick test: shine torch inside with door closed. See light? Seal failed (fix £80–£200). No light? Suspect low charge (call engineer, £250–£600 repair). Both symptoms feel similar—visual inspection is key.
Yes. Manually defrost: turn off compressor, run defrost cycle (or wait 6–8 hours), ice will drip into drain. Never chip ice—risk of puncturing pipes. Once melted, restart unit. However, if ice recurs within 1 week, defrost cycle is failing (thermostat/timer issue). Call engineer to diagnose. Cost: manual defrost £0; engineer diagnosis £150–£200; repair (thermostat/heater) £300–£600.
Not necessarily. First: clean condenser, check door seal, verify setpoint (see Symptom 3). If compressor still runs constantly after these checks, suspect low refrigerant or expansion valve fault. Call engineer for diagnosis (£150–£200). Repair typically £400–£600. Only consider replacement if repair estimate exceeds £2,000 OR if unit is R404A (retrofit/replace costs similar to repair). An 8-year-old unit has 2–5 years lifespan left; repair is usually justified unless major component failure.
Signs: compressor runs constantly but doesn’t reach setpoint; condenser outlet is barely warm; low-pressure gauge (if visible) reads 20 PSI or below (normal = 30–50 PSI). Diagnosis requires electronic leak detector (engineer tool). Cost: leak detection £80–£150. If small leak found, repair typically £400–£600. If large leak or oil staining visible, damage is more serious—cost £1,000+. Annual leak tests (mandatory under F-Gas) catch problems early.
