Rooftop Unit Not Heating? What GTA Property Managers Should Check Before the Service Call
It's the first cold Monday of November. Tenants on one side of the floor say their office is freezing. The thermostat says 17°C and it's calling for heat. The rooftop unit serving that space is either silent or blowing cool air.
A rooftop unit not heating usually comes down to a short list of causes. A few you can rule out in minutes without opening anything. The rest need a technician. Here's how to tell the difference, and what to have ready when you make the call.
First, When to Stop and Get Help
You smell gas. Don't touch switches or try to restart anything. Get people out, then call your gas utility's emergency line or 911 from outside.
A carbon monoxide alarm is sounding. Get everyone out and call 911.
You see soot or scorch marks on or around the unit. Leave it off and call for service.
It keeps tripping. Safety controls shut a unit down for a reason. If a breaker or reset trips again, stop resetting it.
The checks below stay outside the unit on purpose. In Ontario, work on gas equipment has to be done by a certified gas technician.
Five Checks You Can Make Before Calling
The thermostat or BAS. Is it in heat mode, set above the room temperature and on an occupied schedule? Does it have working batteries, if it uses them? A schedule that didn't change over for the season is a common find.
The breaker. Check the panel for a tripped breaker. Reset it once at most. If it trips again, leave it off.
The filters. When were they last changed? Clogged filters starve the unit of airflow, which can shut the burners down on overheating.
The rest of the building. Is it one unit or several? One unit points to that unit. Several at once points to controls, power or the gas supply.
Recent work. Has anyone been on the roof or worked on the gas line lately? A shutoff left closed or a disconnect left off is a simple fix, but have your technician or the contractor who did the work turn it back on.
Why a Gas Rooftop Unit Stops Heating
A gas-fired unit lights in a set order: the venting fan starts and is proven, the igniter fires, the gas valve opens and a sensor confirms there's a flame. If any step fails, the control board stops and may lock out. These are the usual reasons:
Failed igniter. No ignition means no heat. The unit tries a set number of times, then locks out.
Dirty or failed flame sensor. The burners light, then shut off a few seconds later because the board can't confirm the flame.
Venting problems. A failed inducer motor, a faulty pressure switch, or a vent blocked by ice or debris stops the unit before it tries to light.
High-limit trips. Dirty filters, a broken belt or a failing blower motor reduce airflow, the heat section overheats and the limit shuts off the burners. It often shows up as heat that comes and goes.
An economizer stuck open. The burners may be working, but too much outdoor air comes through and the space never warms up. This is a common reason for an RTU blowing cold air.
One heat stage down. On units with two stages of heat, losing one can go unnoticed on a mild day. The unit falls behind when the temperature drops.
Failed gas valve, board or transformer. These need testing to confirm, so a technician can rule out the simpler causes first.
While the unit is open, the technician should also look at the heat exchanger. A cracked heat exchanger is a carbon monoxide risk, and it changes the conversation from a repair to a bigger decision.
What to Tell the Technician
A few details can shorten the visit and help the technician bring the right parts:
Which unit it is and what space it serves.
When it stopped, and whether anything happened around then, such as a power outage or a storm.
What it's doing: no fan at all, fan blowing cold, or heat that starts and stops.
Any BAS alarms or thermostat messages.
How to reach the roof: hatch, ladder, keys and who can let the technician in.
How to Cut Down on No-Heat Calls
Most of these failures can be spotted before the cold arrives. A proper fall start-up should include:
Firing every stage of heat and checking the temperature rise.
Cleaning or checking flame sensors and igniters.
Inspecting the heat exchanger and clearing the vents.
Changing filters and checking belts.
Making sure the economizer closes the way it should.
A maintenance agreement puts these checks on a schedule. If your building has make-up air units or hot water coils, our post on freeze stat tripping covers the other common winter shutdown.
Rooftop Unit Not Heating Right Now?
Burban Air Systems services rooftop units and the rest of the equipment found in GTA commercial buildings. If your building has no heat, our emergency service team can help. Call (416) 757-3271 or send us a message.
