When your air con gives up in the middle of a sticky British summer, it’s enough to make you crave a good old Scottish cold snap. Whether it’s blowing warm air, leaking water, or making noises like a broken lawnmower, this guide is here to help.
- Why Is My Air Conditioner Not Cooling Properly?
- Why Is My AC Making a Strange Noise?
- What Causes Water to Leak from an Air Con Unit?
- Why Does My Air Conditioner Smell Musty?
- AC Remote Not Working – What to Do
- How to Clean Your AC Filter Safely
- When to Call an Engineer (and What It Might Cost)
- Troubleshooting Flowchart
- Final Tips to Keep Your AC Chilled
We’ll walk you through the most common air conditioning problems faced by UK homeowners and renters, with clear, practical tips you can try before calling in the pros.
From quick filter fixes to odd smells and mysterious puddles, we’ll flag what you can safely sort yourself, and when it’s best to hand it over to an expert.
Let’s get your cool back, one fix at a time…
🔑 Key Takeaways - Common AC Issues and Quick Fixes:
Problem | Likely Cause | Try This First |
No cooling | Dirty filter, low refrigerant | Clean filter, check thermostat |
Strange noises | Loose parts, debris | Inspect for debris (unit off) |
Water leaking | Clogged drain pipe | Call engineer |
Musty smell | Mould in the filter/coils | Clean filter, ventilate |
Remote not working | Dead batteries, signal issue | Replace batteries, reset the remote |
Loud humming | Fan motor issue | Call engineer |
Why Is My Air Conditioner Not Cooling Properly?
There’s nothing more maddening than an AC unit puffing out lukewarm air on a blazing July afternoon in London.
If your system isn’t doing its job, don’t sweat just yet - a few common issues might be behind it, and some are easier to fix than you’d think.
[1] Blocked air filter (most common culprit)
A clogged filter restricts airflow, making your AC work harder and cool less, all while draining more energy.
According to the Energy Saving Trust, dirty filters can ramp up running costs and slash performance.
Cleaning it is quick, safe, and often all it takes to get things frosty again (see how-to section below).
“The most common issue we see during heatwaves is blocked filters. Airflow drops, and people think their AC is broken. Nine times out of ten, it’s just overdue a clean.” – Patrick Garner, Head of AC Installs at Heatable
[2] Thermostat issues
If the thermostat’s on the fritz, your unit might think it’s already hit the target temp.
Double-check it’s set to cool mode and the temperature is at least a few degrees lower than your current room temp - for example, 20°C if the room’s at 25°C. For wireless models, swap in fresh batteries to rule out signal dropouts.
[3] Low refrigerant levels
Refrigerant is the fluid that actually chills the air. If levels are low due to a leak or depletion, cooling performance plummets.
This isn’t a DIY job - topping up refrigerant requires an F-Gas certified engineer under UK law (HSE regulations).
[4] Blocked outdoor condenser unit
Leaves, dust, or the odd crisp packet can clog up your outside unit, especially after stormy weather. This stops heat from escaping, leaving your system struggling.
With the unit switched off, gently remove debris using a soft brush or a hose on low pressure. Avoid pressure washers - they can damage the fins.
If you’ve cleaned the filter, checked the settings, and still can’t feel the chill, it’s likely a deeper issue like a refrigerant leak or compressor fault. These need a pro to diagnose and fix. Expect repair costs in the region of £100–£300.
Why Is My AC Making a Strange Noise?
If your air con’s suddenly started clanking, buzzing, or hissing like it’s got a vendetta, don’t just turn up the telly and hope it sorts itself out.
Weird noises are your system’s way of asking for help - and ignoring them could turn a small fix into a wallet-emptying repair.
[1] Buzzing or humming
These sounds usually signal loose parts or a tired fan motor. A loose panel or worn capacitor might be behind the hum, while buzzing from the motor could point to something more serious.
Power off the unit at the mains and check for anything obviously loose that you can tighten.
Still noisy? You’re likely dealing with an electrical or motor issue that needs a pro.
[2] Rattling
Sounds like something’s rattling around in there? It probably is. Outdoor units often collect twigs, leaves, and general garden chaos, especially after a windy spell.
With the unit safely switched off, you can clear out any visible debris with a soft brush or gentle shake.
If it keeps rattling, it might be an internal component that’s come loose. Don’t go poking around - best leave that to a qualified engineer.
[3] Hissing or gurgling
These are the red flags. A hissing or bubbling sound could mean a refrigerant leak.
Refrigerant isn’t just tricky - it’s regulated and potentially harmful. This one’s not a DIY job, so get an F-Gas-certified engineer on it pronto.
Catching a noise early can save you from bigger problems like compressor failure or total system breakdown. Don’t ignore it - sort it.
Safety reminder:
Always power down your AC fully before inspecting anything, and never touch electrics or sealed parts.
If the noise is persistent, book a proper service with a trusted engineer, and get your unit back to whisper-quiet where it belongs.
What Causes Water to Leak from an Air Con Unit?
A leaking air conditioner might seem like a minor nuisance - until it starts warping your floorboards or staining the ceiling. While leaks are common, they’re rarely safe for DIY fixes.
Here’s what could be going on behind that unwelcome drip:
[1] Blocked drain pipe
Your AC pulls moisture from the air and funnels it away via a small drainage pipe.
Over time, that pipe can clog with dust, algae, or even the odd critter, causing water to back up and spill inside.
Unblocking it often means dismantling parts of the unit, so it’s best left to an engineer. DIY attempts can damage the internals or void your warranty.
[2] Frozen evaporator coil
When airflow is restricted (usually due to a filthy filter) or refrigerant levels run low, the evaporator coil can freeze over. Once it thaws, excess water may overflow the drain pan and start leaking.
Try cleaning your air filter to improve airflow. If that doesn’t solve it, it’s time to have the coil and refrigerant checked by a professional.
[3] Poor installation
If the indoor unit isn’t perfectly level, water won’t drain properly - it’ll pool and eventually leak.
Repositioning or rebalancing the unit is not a DIY job. An engineer can quickly assess and correct this during a service.
Even a small leak can lead to costly water damage if ignored. Most AC leak repairs fall in the £100–£250 range - far less than the cost of new flooring or mould remediation.
Why Does My Air Conditioner Smell Musty?
If your AC smells like damp socks or a forgotten gym bag, don’t ignore it - musty odours are usually a sign of mould or mildew lurking somewhere inside.
The most common cause? A dirty air filter or evaporator coil.
Moisture gets trapped, mould starts growing, and every time you switch the unit on, that lovely aroma gets wafted into your room.
Cleaning the filter (see steps below) is the first thing to try. Once done, run the system on fan-only mode for 30 minutes to help dry out internal components, and crack a window for good measure.
A dirty drain pan is another culprit. If water collects and stagnates, bacteria and mildew follow. This isn’t something you can easily reach, so you’ll need a professional to inspect and clean or replace it.
Also, check that vents aren’t blocked by furniture or curtains - restricted airflow can make smells worse and reduce performance.
If the smell lingers after cleaning, mould may have crept deeper into the coils or ductwork. At that point, a professional deep clean is the fix, typically costing around £60–£150.
Heatable tip: Keep things fresh with regular maintenance - see our filter cleaning guide below and schedule a pro service once a year.
AC Remote Not Working – What to Do
If your AC remote’s giving you the silent treatment, don’t panic; most issues have quick fixes.
Step 1: Check the batteries
Dead or dying batteries are the top cause. Replace them (usually AA or AAA) and make sure they’re inserted the right way around.
Step 2: Check the signal
AC remotes use infrared, so they need a clear line of sight. Stand within 5 metres of the unit and point directly at the sensor - no walls or furniture in the way.
Step 3: Try a reset
Some remotes need resyncing with the unit. Look for a reset button or try holding the power button for 5–10 seconds. If you’ve lost the manual, search online using the make and model.
Still nothing?
The remote might be faulty. Universal replacements cost around £10–£30, or you can order the exact model from the manufacturer.
If the unit itself isn’t responding, the issue might be the control board - that’s a job for an engineer, and it could run £150–£400 depending on the fault.
How to Clean Your AC Filter Safely
A dirty air filter is behind most air con complaints, from weak airflow to musty smells and rising energy bills.
The good news? Cleaning it is quick, safe, and can save you serious cash.
How to clean your AC filter:
1. Switch it off
Unplug the unit or turn it off at the mains.
2. Locate the filter
On most wall-mounted units, it’s just behind the front panel. Your manual will show you where.
3. Remove and clean
Slide out the filter, vacuum off loose dust, then wash it gently with lukewarm water and a drop of mild soap. Rinse well.
4. Dry fully
Let it air dry for 2–3 hours - never reinstall it wet.
5. Pop it back in
Make sure it’s secure before switching the unit back on.
Heatable tip: Clean your filter every 1–2 months during high use. A clean filter helps your AC run efficiently and keeps your energy bills in check.
⚠️ Warranty warning: Only clean the filter. Leave internal components to the pros.
When to Call an Engineer (and What It Might Cost)
Some AC issues are too risky or complex for DIY, and leaving them can lead to much bigger (and costlier) problems.
Call in a professional if you notice:
Refrigerant leaks (hissing, no cooling, ice build-up)
Electrical issues (burning smells, tripped breakers)
Persistent leaks, odours, or strange noises after basic troubleshooting
Major faults, like compressor or fan motor failure
Typical AC repair costs in the UK:
Service/clean: £60–£150
Refrigerant top-up: £100–£300
Major repairs (e.g. compressor): £200–£600
Emergency call-out: Add £50–£100
Troubleshooting Flowchart
Problem | Likely Cause | Quick Fix (If Safe) | Call The Engineer? |
No cooling | Dirty filter, low refrigerant | Clean filter, check thermostat | If no improvement |
Strange noise | Loose parts, debris | Inspect for debris (unit off) | For buzzing/hissing |
Water leaking | Clogged drain, frozen coil | None | Yes |
Musty smell | Mould in the filter/coils | Clean filter, ventilate | If the smell persists |
Remote failure | Dead batteries, signal issue | Replace batteries, reset | If unit doesn’t respond |
Final Tips to Keep Your AC Chilled
Want your air con to stay crisp, quiet, and drama-free?
Here’s how to keep it that way:
Clean your filter every 1–2 months, more often during heatwaves or if you’ve got pets or pollen around.
Set your temperature between 20–22°C for the best balance of comfort and efficiency, as advised by the Energy Saving Trust.
Book a professional service once a year (£150–£300) to catch small issues before they turn into big ones.
Most importantly, stay safe. Don’t mess with electrics or refrigerant - leave that to an F-Gas-certified engineer.
Still sweating?
Don’t let a moody AC spoil your summer.
Book an AC replacement with Heatable today.
Next Steps For Your AC Journey:
When planning to install air conditioning for your home, there are several important factors to consider. Make sure to refer to the following guides to help you make informed decisions:
To dive deeper into these topics, head over to our advice section, check out our YouTube channel for informative videos.
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