24/7 Emergency HVAC Repair in London (MVHR, FCU, AHU): Common Faults + Fast Fixes

• Posted By: Francis Akinola
• Posted on: 2026-03-31

 

If your ventilation or air conditioning fails, it can quickly turn into a health, comfort, and compliance issue—especially in offices, residential blocks, and healthcare environments. ARC Facilities provides 24/7 emergency HVAC repair across Greenwich, South East London, and Greater London, with fast triage and clear communication from qualified engineers.

 

When an HVAC issue becomes an emergency

 

Call for urgent support if you notice:

 

Complete loss of ventilation or cooling/heating in occupied areas

Burning smells, repeated tripping, or electrical fault symptoms linked to HVAC equipment

Water leaks from fan coil units (FCUs) or air handling units (AHUs)

Sudden loud noise/vibration, fan failure, or overheating

Poor air quality complaints (stuffy rooms, condensation, mould risk)

 

 

Emergency MVHR faults (common symptoms + likely causes)

 

 

MVHR (Mechanical Ventilation with Heat Recovery) systems are common in new builds and retrofits. When they fail, indoor air quality can drop quickly.

 

1) MVHR is not running at all

 

 

Common causes:

 

Isolator switched off / blown fuse

Control fault or failed power supply

Fan motor failure

 

Fast fixes (safe checks):

 

Check the MVHR isolator switch is on

Check if the unit is showing any fault code on the controller

If safe to do so, confirm filters aren’t completely blocked

 

2) MVHR is noisy or vibrating

 

Common causes:

Worn bearings or failing fan

Loose mounting or ductwork issues

Blocked filters increase the strain

 

Fast fixes:

Reduce load by checking filters (replace if heavily clogged)

Book an urgent inspection to prevent full fan failure

 

 

 

                                                                                                                               

3) Poor airflow / rooms feel stuffy

 

Common causes:

Blocked filters or valves

Duct restrictions

Incorrect settings after a power cut

 

 

Fast fixes:

Confirm boost mode isn’t stuck off

Check filters and visible vents for blockage

Arrange a service visit to test airflow and balance

 

 

Emergency FCU faults (fan coil units)

 

 

FCUs are common in offices and mixed-use buildings. Failures can affect comfort quickly and can also create leak risks.

 

 

1) FCU leaking water

 

Common causes:

Blocked condensate drain

Frozen coil / defrost issue

Damaged tray or pipework

 

Fast fixes:

Switch the unit off to prevent further damage

Contain the leak and protect the electrics below

Call for urgent attendance—leaks can escalate fast

 

2) FCU running but not cooling/heating

 

Common causes:

Valve actuator failure

Control/BMS signal issue

Coil fouling or airflow restriction

 

Fast fixes:

Note whether the fan runs and if any error lights show

Record zone/room affected and time the issue started

 

3) FCU not responding to controls

 

Common causes:

Thermostat/controller fault

Power supply issue

Communication fault (BMS)

 

Fast fixes:

Check local controller power (if accessible)

Provide building management with any recent changes or outages

 

Emergency AHU faults (air handling units)

 

AHUs support whole floors or buildings—downtime can be serious.

 

1) AHU fan failure/unit trips

 

Common causes:

Motor overload

Belt failure (belt-driven systems)

Electrical fault or safety interlock activation

 

Fast fixes:

Do not repeatedly reset trips—this can worsen damage

Capture any fault messages and note unusual sounds/smells

 

2) AHU delivering poor air quality

 

Common causes:

Filter blockage

Damper fault

Heat exchanger or coil issues

 

Fast fixes:

Check maintenance logs (last filter change)

Arrange urgent inspection to restore safe ventilation

 

What to have ready when you call (speeds up diagnosis)

 

To help us triage quickly, share:

 

Equipment type (MVHR / FCU / AHU) and brand/model (if known)

Symptoms (not running, leaking, noisy, poor airflow)

Any fault codes or controller messages

Site address and access details (plant room location, permits)

Whether the issue affects a single room, a floor, or the whole building

 

Our emergency response coverage

 

ARC Facilities is based in Greenwich (SE18) and supports urgent HVAC call-outs across:

Greenwich and South East London

Greater London

Essex and Kent (as required)

If you’re dealing with an urgent HVAC breakdown, we’ll prioritise attendance based on risk and impact, and keep you updated throughout.

 

FAQs: Emergency HVAC repair in London

 

How fast can you attend an emergency HVAC call-out?

In London, emergency attendance is typically prioritised for high-risk issues (loss of ventilation, leaks, electrical symptoms). Share the details above so we can triage accurately and respond as fast as possible.

 

Do you repair MVHR systems in residential blocks and new builds?

Yes—MVHR is a common call-out for airflow issues, fan failure, and noisy units. We support diagnostics, repair, and servicing.

 

Can you help if the issue might be linked to controls or BMS?

Yes. Many FCU/AHU issues are control-related. If you can share recent changes, alarms, and affected zones, it speeds up fault-finding.

 

Do you offer planned maintenance to prevent emergencies?

Yes. Preventive maintenance reduces breakdowns and helps keep systems efficient, compliant, and reliable—especially for AHUs and multi-zone FCU setups.

 

Need urgent HVAC help in Greenwich or Greater London?

If your MVHR, FCU, or AHU has failed and you need urgent support, contact ARC Facilities for 24/7 emergency HVAC repair in Greenwich, South East London, and Greater London.

Tip: If it’s safe to do so, take a photo of the unit label and any fault code on the controller before calling—this can speed up diagnosis