Protect the
sensors.
Garage wash-downs are routine maintenance. They are also, in our service records, one of the most reliable ways to kill a set of carbon monoxide sensors. The reason is simple: a CO sensor has to be open to the air to work, so there is a direct path from a pressure washer wand to the sensing cell.
Before the crew arrives
- Locate every sensor. They are usually ceiling or wall mounted at breathing height or lower, spread across every level, plus the control panel and any remote displays.
- Cover each sensor head with a bag or purpose-made cover, secured so it cannot blow off mid-wash.
- Put it in the scope of work. Tell the wash contractor in writing not to spray directly at sensors, the panel, or upward at ceiling devices, and to keep the wand back from them.
- Tell whoever monitors the building. Covered sensors and a wet garage often produce alarms and faults during the work.
The critical part: covers come off the same day the wash finishes. A bagged sensor detects nothing. We have walked into garages and found sensors still bagged from a wash-down months earlier, which means the building has had no CO detection at all in the interim, and no record that would survive an inspection or an incident.
After the wash
Check the panel. Faults that appear during or right after a wash-down are a strong signal of water intrusion. But the more dangerous outcome is the quiet one: a sensor that survived the soaking, still reports a number, and is now reading incorrectly. Nothing on the panel tells you that. The only way to find it is certified test gas.
If your building washes the garage on a schedule, the practical move is to line the annual CO service up to follow the wash. You are required to inspect and test the gas detection system at least annually anyway (California Fire Code §916.11, with sensor calibration on the manufacturer’s schedule), so scheduling that visit for the weeks after the wash-down means one trip covers both the compliance requirement and the water check.
Signs a sensor took on water
- Fault or trouble on one or more addresses that appeared during the wash
- Readings that sit high and do not clear once the garage dries
- Exhaust fans running continuously after the wash-down
- Visible staining, corrosion or moisture at the sensor housing
ACES Monitoring calibrates and repairs garage gas detection systems nationwide and can coordinate the visit around your wash schedule.
Sources: California Fire Code §916.11 · sensor manufacturer service literature.
Common questions
Does power washing damage CO sensors?
Yes, frequently. Electrochemical CO sensors are open to the air by design, and direct spray or heavy mist can flood the cell, corrode the electronics and cause permanent failure. Water intrusion is one of the most common causes of multi-sensor faults we are called out for.
How do I protect garage CO sensors during pressure washing?
Cover each sensor head before the crew starts, keep the wand away from sensors and the panel, avoid spraying upward at ceiling-mounted devices, and remove every cover the same day the wash finishes. A covered sensor is a blind sensor, so it cannot be left bagged.
What if the panel is in alarm or fault after a wash-down?
Do not just silence it. Moisture can cause both immediate faults and readings that drift for days afterward. Have the sensors checked and calibrated, and replace any that fail to respond to test gas.
Should the wash contractor cover the sensors?
Do not assume they will, and do not assume they know which devices are sensors. Assign it explicitly, in writing, and confirm the covers are off afterward.
Talk to a gas monitoring specialist
Tell us the building and how many sensors you have. We will tell you what service it needs and what it costs, no pressure.