Wipe down interior shelves and glass with a clean microfibre cloth and warm water + mild detergent. Check the deli thermometer on the door for temperature stability (should read +2 to +4°C for chilled). Empty the drip tray (base of unit) — bacteria grow in standing water and create biofilm smell. Rotate older stock to front (FIFO rule). Any sudden temperature jump? Do not wait — check the door seal and condenser immediately. Do this every morning before stock rotation.

This is where the money is made. Pull out all removable shelves and soak them in hot water + sanitiser (Ecolab or equivalent food-contact safe). While they soak, use a soft brush (or old toothbrush for tight spaces) to brush the condenser fins horizontally — do this from the back of the unit, never push dirt into the fins. Vacuum up the dust with a handheld vac. Check the door gasket (seal) for cracks, hardening, or mould — if mould is visible, wipe with a cloth damp in vinegar solution. Test all LED lights by looking at each shelf edge — they should be bright white. Reassemble shelves. This is the single most effective maintenance task. Do this every Sunday evening or Monday morning without fail.

This requires a second person and 30 minutes of downtime. Turn off the unit. Move it away from the wall (recruit a colleague — it’s heavy). Vacuum the floor and wall behind the unit where the condenser exhaust blows — lint and dust accumulate here. Check that the defrost cycle actually drains — pour 500 ml of water down the internal drain hole (usually at the base inside the unit) and watch it flow out the external drain tube. If it’s slow, the drain tube is clogged — use a plumbing snake or compressed air to clear it. Test the door auto-close if it has one (gravity hinges) — the door should close smoothly within 3 seconds. Any sticking = hinge maintenance or gasket swell. Push the unit back. This is the month-end full system health check.

Book an F-Gas certified engineer for a full refrigerant system inspection. They will: check suction and discharge pressures (must be within manufacturer spec, typically +0.5°C of set point); test the defrost termination sensor; check the control board with a multimeter; and assess gasket hardness. If the gasket is hard or tacky, replace it (£40 part, £60 labour). This is the only maintenance that MUST be done by a licensed engineer — never try this yourself. F-Gas certificate numbers are logged; penalties for unlicensed work are severe. Schedule this in the first week of months 3, 6, 9, and 12 of the year.

At the 12-month mark, arrange a full service. This includes: PAT (portable appliance test) — electrical safety inspection with test certificate; F-Gas annual check-in (your engineer updates the refrigerant log); full gasket replacement (even if it passed the quarterly check, replace preventatively); replacement of all o-rings and seals on the refrigerant lines (they dry out over 12 months); deep clean of the evaporator coils (blown with compressed air from inside the unit); and a full temperature calibration run (the unit is run for 4 hours at setpoint, temperature logged every 15 minutes to confirm stability). This is your “zero-hours reset” — the unit comes off an annual service running like new.

Diagnosis steps: (a) Check the condenser fins immediately — look for dust, cardboard fibres, or grease clogging the horizontal fins. Use a torch. (b) If blocked, brush them and retest after 30 minutes. Temperature should drop back. (c) If temperature doesn’t recover, feel the compressor housing — is it hot to touch? That’s a sign of high refrigerant pressure (could be blocked condenser, could be low refrigerant, could be bad pressure switch). (d) Check the door seal — run a playing card around the gasket. If the card slides through easily anywhere, you have a leak (hot air leaks in, unit works harder, temperature rises). (e) If none of the above, the refrigerant charge is likely low — a leak somewhere. Call an F-Gas engineer immediately. Do not attempt to top up yourself.

Diagnosis steps: (a) This is almost always a defrost cycle failure. The unit is supposed to heat the evaporator every 8 hours for 10–20 minutes to melt frost; if this doesn’t happen, frost accumulates. (b) Check if the defrost termination sensor is ice-covered — use a cloth to carefully wipe it clean. If the frost was covering the sensor, the system may have already run a defrost cycle and recovered. (c) If frost returns within 12 hours, the defrost timer is broken. This is an engineer fix (£150–£220, 1 hour). (d) Check the drain — a blocked drain trap will cause ice build-up below the evaporator. Pour warm water down the internal drain. (e) If the door is self-closing and sticks slightly open, warm moist air gets in and refreezes. Check hinge tension.

Diagnosis steps: (a) Check the condenser fins first — this is the #1 cause. Blow them clean with compressed air. (b) Measure the ambient room temperature — if it’s above 30°C (in a kitchen with no air con in summer), the unit may legitimately run harder, but shouldn’t be 24/7 constant. If ambient is normal (18–25°C) and the compressor is still constant, move to step (c). (c) Check the setpoint temperature — is it set to 0°C or lower? If set too cold, the compressor cycles forever trying to reach an impossible temperature. Adjust to +3°C and wait 2 hours. (d) If still running constantly, the refrigerant charge is likely low — the unit chills to the set point, but leaks mean it drops back below setpoint immediately, triggering the compressor again. Call an engineer. (e) Check that the condenser fan is actually running — you should hear it. If silent, the fan motor is dead (£180–£240 replacement).

Diagnosis steps: (a) Check if the unit is powered on — do other LEDs still light? If only one shelf is dark and others are bright, the LED strip on that shelf has failed. (b) LED strips are usually under warranty (2–3 years) and cost £35–£60 to replace. Turn off the unit. Locate the clip or screw holding the LED strip in place at the shelf edge. Remove and slide in a new strip. Reconnect the plug. Test. (c) If multiple shelves are dark and the LED transformer is buzzing, the transformer is failing (£45–£80 part, £40 labour). (d) If all LEDs are out, check the main circuit breaker on the unit — it may have tripped. Flip it back on.

Diagnosis steps: (a) Check the hinge tension — there’s usually a screw or Allen key adjustment on the hinge. On a Polar G-series, there’s a tension dial on the top hinge. On Tefcold units, there’s an Allen screw. Tighten gently. (b) If tightening doesn’t help, the hinge spring is broken — the door needs a new hinge assembly (£90–£140 for top and bottom hinges, 45 minutes labour). (c) Check if the door is rubbing the frame — sometimes the gasket swells and creates friction, making the door stick. If it sticks open, the hinge can’t pull it closed. In this case, the gasket needs replacement (see quarterly maintenance).

Diagnosis steps: (a) First, check if the drip tray is overflowing — underneath the unit there’s a removable tray that collects condensate. Empty it. Refill it with water to test if it drains. (b) If water pours out the external drain tube, the system is working; the tray was just full. Empty it more frequently (every 2–3 days in busy areas). (c) If water doesn’t drain from the tray, the drain hole is blocked. Use a thin wire or pipe cleaner to clear it from inside the unit. (d) Check the internal drain tube — on open-fronted units, condensate runs down the back wall into a drain channel at the base. If this is blocked with dirt or food debris, water spills out the sides. Use a cloth to wipe the channel clean, then pour warm water down to test flow.

Diagnosis steps: (a) The smell is almost always biofilm growing in standing water in the drain pan or drain line. (b) Empty and scrub the drip tray with a brush and mild bleach solution (10% bleach, 90% water). Rinse thoroughly. (c) Pour warm water + a capful of household bleach down the internal drain to kill biofilm in the line itself. Let it sit for 10 minutes, then flush with warm water. (d) Check for forgotten food — on open-front units, spilled food can wedge in the evaporator housing and rot. Look behind and below the shelves. (e) If the smell persists after drain cleaning, the evaporator coil itself may have biofilm — this requires an engineer to blow out with compressed air (£100–£150).

Diagnosis steps (brand-specific): (a) Polar G-series: Red alarm light = high-temperature alarm (usually condenser blocked or door seal failed). Green OK light = system normal. (b) Tefcold: Numeric codes: E1 = temperature sensor fault (defrost termination sensor failed, call engineer); E2 = compressor overload (high pressure, likely blocked condenser); E3 = control board fault (board needs replacement, £280–£400). (c) Frost-Tech: Check the SD card log in the control panel — it records temperature every 15 minutes and can identify exactly when the fault started. Download it to a PC. (d) Williams: Beeping alarm with no light = low refrigerant pressure. Check the condenser and door seal. Solid red light = high pressure. (e) Always try a power reset first: turn off the unit at the wall for 30 seconds, turn back on. If the error clears, it was a transient glitch. If it returns, the sensor or board is failing and needs an engineer (£150–£350 depending on part).