Another batch of TripAdvisor reviews just dropped. “Room was lovely but the air conditioning didn’t work.” “AC was making a terrible noise all night.” And the classic: “The room smelled musty — like damp.” Three different complaints, three different rooms, all pointing at the same underlying issue — HVAC maintenance that’s been allowed to slip.
Hotel room AC complaints don’t just annoy guests. They damage your ratings, suppress bookings, and cost significantly more to fix reactively than they would have cost to prevent. Here’s what’s actually going wrong behind the grille and how to stop these complaints before they hit the internet.
We handle this type of problem frequently for businesses in West London and the surrounding area. If your system is showing these symptoms, our PPM team can usually diagnose the root cause on the first visit.
Dirty Filters — The Number One Culprit
Every fan coil unit in every guest room has an air filter. When that filter clogs with dust, the unit can’t move enough air. The room doesn’t cool properly, the fan runs louder trying to compensate, and the guest notices both problems immediately. In severe cases, the evaporator coil ices up behind the clogged filter, and the unit stops producing any meaningful cooling at all.
Housekeeping staff are in every room daily. They should be trained to visually check the fan coil unit and flag rooms where the filter looks dirty or the unit sounds abnormal. Maintenance should be changing filters on a fixed schedule — quarterly at minimum, monthly in high-occupancy rooms or during peak season. This single action prevents more guest complaints than every other item on this list combined.
Fan Coil Unit Valve Stuck
Hotel HVAC systems are typically either 2-pipe or 4-pipe configurations. In a 2-pipe system, the same pipework carries either chilled water for cooling or hot water for heating, switched seasonally. In a 4-pipe system, both are available year-round. Each fan coil unit has a motorised valve controlled by the room thermostat that opens and closes to regulate water flow through the coil.
These valves seize. Particularly in rooms that sit unoccupied for extended periods, the valve can stick in the closed position. The fan runs, air blows, but it’s room-temperature air because no chilled or hot water is flowing through the coil. The guest sets the thermostat to 18°C, waits twenty minutes, and nothing changes. They call reception, and now you have an unhappy guest and a maintenance call-out during service hours.
During annual maintenance, every valve on every fan coil unit should be cycled through its full range of travel. This keeps the mechanism free and catches valves that are starting to stick before they seize completely. Once a valve has fully seized, it needs replacing — a straightforward job requiring isolation of the water circuit serving that unit.
Thermostat Problems
Hotel room thermostats endure more abuse than most HVAC components. Guests prod every button, adjust settings they don’t understand, and occasionally attempt creative solutions to perceived temperature problems. Battery-powered thermostats go flat. Wired thermostats get knocked off the wall during luggage handling. Guests switch units off at the isolator behind the curtain and don’t mention it at checkout.
Dead batteries are the single most common thermostat-related complaint. The display goes blank, the unit doesn’t respond, and the guest reports that the AC is broken. Maintenance should replace thermostat batteries on a fixed schedule — every six months. It takes 30 seconds per room and eliminates an entire category of complaints.
Guest confusion is the other major factor. Some guests switch the unit to “Fan Only” without realising they’ve disabled the cooling function. Others can’t distinguish between heating and cooling modes. Clear, simple operating instructions positioned near the thermostat help considerably. Better still, install tamper-resistant controllers that limit adjustable parameters to temperature setpoint only.
The Musty Smell — Condensate Tray Overflow
That damp, musty odour guests complain about almost always originates from the condensate tray inside the fan coil unit. When the unit cools air, it pulls moisture out of the room atmosphere. This condensation collects in a tray beneath the coil and drains away through a small pipe. If the drain blocks — or the tray doesn’t empty properly — stagnant water sits there growing mould, bacteria, and biofilm. Every time the fan runs, it pushes air across that contaminated water and straight into the guest room.
Condensate trays should be cleaned and flushed at every service visit. The drain line needs checking for blockages. Condensate tray tablets — slow-release biocide blocks dropped into the tray — inhibit microbial growth between service visits. They cost pennies per room and prevent the musty smell that generates one-star reviews. Most hotels don’t bother with them until the complaints become impossible to ignore.
Seasonal Changeover Failures on 2-Pipe Systems
Hotels running 2-pipe fan coil systems face a specific vulnerability each spring and autumn: the seasonal changeover. When the central plant switches from heating mode to cooling mode (or vice versa), every individual fan coil unit needs to be verified. Valves checked, controls confirmed, air purged from the pipework, and thermostats set to the correct mode.
We have written a separate guide on AC thermostats reading the wrong temperature which covers a related failure mode worth checking. Similarly, our article on air conditioning leaking water explains another common cause of the same underlying issue.
We’ve attended hotels in June where half the rooms have no cooling because the changeover in March wasn’t completed properly. Some rooms were missed. Others had air locks in the pipework. A few had valves that seized during the changeover. Each room needs individual verification — there’s no shortcut. Doing it properly in spring prevents a summer full of complaints.
Guest Operating Errors
Not every complaint represents a genuine fault. Many guests don’t understand hotel AC controls, especially international visitors accustomed to different systems. Common misunderstandings include expecting instant cooling from a fan coil unit that takes several minutes to reach temperature, not realising the unit only operates when the key card is in the slot, or setting the thermostat below the system’s minimum cooling setpoint and wondering why the room won’t go any colder.
Clear, multilingual operating instructions in the room reduce these complaints measurably. A laminated card near the thermostat explaining the basics — insert key card, set desired temperature, allow five minutes — saves your maintenance team dozens of unnecessary call-outs per month during peak season.
ADK’s Hotel PPM Contracts
We run planned preventive maintenance contracts for hotels across London. Quarterly filter changes, annual deep cleans of every fan coil unit, valve exercising, condensate tray treatment, thermostat battery replacement, and full seasonal changeover support. Our hotel clients see guest AC complaint rates drop by up to 90% within the first year of a PPM contract. That’s not a sales figure — it’s what actually happens when the maintenance is done properly.
If your guests are complaining about the AC, the problem isn’t the guests. Call ADK on 0207 801 0808 and let’s fix it properly.