Service
Air Pressure Switch Repair & Replacement
The differential air pressure switch is the part that proves the kitchen extract is moving air. It is also the most common failure point on a gas interlock — a £30 switch that stops a whole kitchen cooking when it drifts or blocks.
- Fan and gas proving air pressure switches in stock today
- Set to a measured duct pressure, not wound down until the fault clears
- Interlock retested and certified after every switch change
How it works
The switch senses the pressure difference across the extract fan or a duct tapping through two small sensing tubes. When the fan runs and the differential exceeds the set point, the switch contacts make and the interlock panel accepts ventilation as proven, energising the gas solenoid valve. Lose the differential and the contacts break and the gas closes.
Common faults
| Fault | Symptom | Repair |
|---|---|---|
| Set point too high | Gas drops out with the fan running normally | Measure and reset within range |
| Sensing tubes blocked or greasy | Random fan faults, worse after cleaning is skipped | Clean or replace tubing and tappings |
| Tubes on the wrong ports | Never proves, or proves with the fan off | Refit high and low correctly |
| Perished diaphragm | Sticky, slow or dead switching | Replace the switch |
| Corroded or loose terminals | Intermittent trips mid-service | Re-terminate and test |
| Wrong switch range for the duct | Cannot be set reliably at all | Fit a switch with the correct pressure range |
What a proper repair includes
- Measured differential pressure across the fan at operating condition
- Set point documented, with a sensible margin above proven airflow
- Sensing tubes renewed and routed so grease and condensate cannot collect
- Full interlock function test: fan fail, emergency stop and valve closure
- Certificate for the compliance file
If you can smell gas
- Turn off the gas at the emergency control valve and press the emergency stop button
- Do not switch anything electrical on or off, and do not use naked flames
- Open doors and windows, evacuate and keep people clear
- Call the National Gas Emergency Service on 0800 111 999
- Only then call us to make the installation safe and return it to service
Frequently asked questions
Can I adjust the pressure switch myself?
It should be set against a measured duct pressure by a competent engineer. Adjusting it by trial and error can leave the system proving ventilation that is not actually there.
How long do air pressure switches last?
Typically five to ten years in a kitchen environment, but grease, heat and dirty filters shorten that considerably. They are checked at every annual interlock service.
Do you carry them in stock?
Yes — fan proving and gas proving air pressure switches are stock items, fitted same day in most cases.
Is a current monitor better?
A fan current monitor proves the motor is loaded but not that air is moving; a differential pressure switch or airflow sensor is the stronger proof and is what we normally recommend.
Related guides
Sensors & Controls
Air pressure switches, airflow sensors, current monitors, e-stops.
Interlock Fan Fault
Fan fail lamps, airflow switch faults and extract failures.
Gas Shuts Off When Extraction Starts
Pressure switch set wrong, ducting or make-up air imbalance.
Proving System Faults
Failed pressure proof, leak detected and reset lockouts.
Servicing & Testing
Annual interlock testing, certification and planned maintenance.
Gas Interlock Systems
The pillar guide: how interlocks work, standards and fault-finding.
Parts in stock — ready to fit
Held in UK stock and carried on our vans, so most jobs are fixed in one visit.
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